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Osterman WHA, Hill A, Hagan JG, Whitton J, Bacon CD, Bjorkman AD. Rethinking pathways to the dioecy-polyploidy association: Genera with many dioecious species have fewer polyploids. AMERICAN JOURNAL OF BOTANY 2024; 111:e16318. [PMID: 38654555 DOI: 10.1002/ajb2.16318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Revised: 03/19/2024] [Accepted: 03/19/2024] [Indexed: 04/26/2024]
Abstract
PREMISE Numerous studies have found a positive association between dioecy and polyploidy; however, this association presents a theoretical conflict: While polyploids are predicted to benefit from self-reproduction for successful establishment, dioecious species cannot self-reproduce. We propose a theoretical framework to resolve this apparent conflict. We hypothesize that the inability of dioecious species to self-reproduce hinders their establishment as polyploids. We therefore expect that genera with many dioecious species have fewer polyploids, leading to a negative association between polyploidy and dioecy across genera. METHODS We used three publicly available databases to determine ploidy and sexual systems for 131 genera and 546 species. We quantified (1) the relationship between the frequency of polyploid species and the frequency of dioecious species across genera, and (2) the proportion of polyploids with hermaphroditism and dioecy across species, adjusting for phylogenetic history. RESULTS Across genera, we found a negative relationship between the proportion of polyploids and the proportion of dioecious species, a consistent trend across clades. Across all species, we found that sexual system (dioecious or not) was not associated with polyploidy. CONCLUSIONS Polyploids are rare in genera in which the majority of species are dioecious, consistent with the theory that self-reproduction favors polyploid establishment. The low frequency of polyploidy among dioecious species indicates the association is not as widespread as previously suggested. Our findings are consistent with previous studies identifying a positive relationship between the two traits, but only if polyploidy promotes a transition to dioecy, and not the reverse.
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Affiliation(s)
- Wilhelm H A Osterman
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden
- Gothenburg Global Biodiversity Centre, Gothenburg, Sweden
| | - Adrian Hill
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden
- Gothenburg Global Biodiversity Centre, Gothenburg, Sweden
| | - James G Hagan
- Gothenburg Global Biodiversity Centre, Gothenburg, Sweden
- Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden
| | - Jeannette Whitton
- Department of Botany and Biodiversity Research Centre, The University of British Columbia, Vancouver, Canada
| | - Christine D Bacon
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden
- Gothenburg Global Biodiversity Centre, Gothenburg, Sweden
| | - Anne D Bjorkman
- Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden
- Gothenburg Global Biodiversity Centre, Gothenburg, Sweden
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2
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Schedler M, Reutemann AV, Hojsgaard DH, Zilli AL, Brugnoli EA, Galdeano F, Acuña CA, Honfi AI, Martínez EJ. Alternative Evolutionary Pathways in Paspalum Involving Allotetraploidy, Sexuality, and Varied Mating Systems. Genes (Basel) 2023; 14:1137. [PMID: 37372317 DOI: 10.3390/genes14061137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2023] [Revised: 05/17/2023] [Accepted: 05/22/2023] [Indexed: 06/29/2023] Open
Abstract
The genetic systems of Paspalum species have not been extensively studied. We analyzed the ploidy, reproductive mode, mating system, and fertility of four Paspalum species-Paspalum durifolium, Paspalum ionanthum, Paspalum regnellii, and Paspalum urvillei. An analysis of 378 individuals from 20 populations of northeastern Argentina was conducted. All populations of the four Paspalum species were pure tetraploid and had a sexual and stable reproductive mode. However, some populations of P. durifolium and P. ionanthum showed low levels of apospory. Populations of P. durifolium and P. ionanthum had low seed sets under self-pollination but were fertile under open pollination, showing that self-incompatibility likely caused self-sterility. In contrast, populations of P. regnellii or P. urvillei showed no evidence of apospory, and seed sets in both self- and open pollination conditions were high, suggesting that they are self-compatible due to the absence of pollen-pistil molecular incompatibility mechanisms. The evolutionary origin of the four Paspalum species could explain these differences. This study supplies valuable insights into the genetic systems of Paspalum species, which could have implications for their conservation and management.
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Affiliation(s)
- Mara Schedler
- Instituto de Botánica del Nordeste (IBONE-UNNE-CONICET), Facultad de Ciencias Agrarias, Universidad Nacional del Nordeste (FCA-UNNE), Corrientes 3400, Corrientes, Argentina
| | - Anna Verena Reutemann
- Instituto de Botánica del Nordeste (IBONE-UNNE-CONICET), Facultad de Ciencias Agrarias, Universidad Nacional del Nordeste (FCA-UNNE), Corrientes 3400, Corrientes, Argentina
| | - Diego Hernán Hojsgaard
- Taxonomy & Evolutionary Biology, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), 06466 Gatersleben, Germany
| | - Alex Leonel Zilli
- Instituto de Botánica del Nordeste (IBONE-UNNE-CONICET), Facultad de Ciencias Agrarias, Universidad Nacional del Nordeste (FCA-UNNE), Corrientes 3400, Corrientes, Argentina
| | - Elsa Andrea Brugnoli
- Instituto de Botánica del Nordeste (IBONE-UNNE-CONICET), Facultad de Ciencias Agrarias, Universidad Nacional del Nordeste (FCA-UNNE), Corrientes 3400, Corrientes, Argentina
| | - Florencia Galdeano
- Instituto de Botánica del Nordeste (IBONE-UNNE-CONICET), Facultad de Ciencias Agrarias, Universidad Nacional del Nordeste (FCA-UNNE), Corrientes 3400, Corrientes, Argentina
| | - Carlos Alberto Acuña
- Instituto de Botánica del Nordeste (IBONE-UNNE-CONICET), Facultad de Ciencias Agrarias, Universidad Nacional del Nordeste (FCA-UNNE), Corrientes 3400, Corrientes, Argentina
| | - Ana Isabel Honfi
- Programa de Estudios Florísticos y Genética Vegetal, Instituto de Biología Subtropical (PEFyGV, IBS-UNaM-CONICET), Posadas 3300, Misiones, Argentina
| | - Eric Javier Martínez
- Instituto de Botánica del Nordeste (IBONE-UNNE-CONICET), Facultad de Ciencias Agrarias, Universidad Nacional del Nordeste (FCA-UNNE), Corrientes 3400, Corrientes, Argentina
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3
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Pretz C, Smith SD. Intraspecific breakdown of self-incompatibility in Physalis acutifolia (Solanaceae). AOB PLANTS 2022; 14:plab080. [PMID: 35079331 PMCID: PMC8783618 DOI: 10.1093/aobpla/plab080] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Accepted: 12/21/2021] [Indexed: 05/13/2023]
Abstract
Variation in mating systems is prevalent throughout angiosperms, with many transitions between outcrossing and selfing above and below the species level. This study documents a new case of an intraspecific breakdown of self-incompatibility in a wild relative of tomatillo, Physalis acutifolia. We used controlled greenhouse crosses to identify self-incompatible (SI) and self-compatible (SC) individuals grown from seed sampled across seven sites across Arizona and New Mexico. We measured 14 flower and fruit traits to test for trait variation associated with mating system. We also quantified pollen tube growth in vivo and tested for the presence of the S-RNase proteins in SI and SC styles. We found that seed from six of the seven sites produced SI individuals that terminated self-pollen tubes in the style and showed detectable S-RNase expression. By contrast, seed from one Arizona site produced SC individuals with no S-RNase expression. These SC individuals displayed typical selfing-syndrome traits such as smaller corollas, reduced stigma-anther distances, and a smaller pollen-ovule ratio. We also found plasticity in self-incompatibility as most of the SI individuals became SC and lost S-RNase expression roughly after 6 months in the greenhouse. While fixed differences in mating systems are known among the SI wild species and the often SC domesticated tomatillos, our study is the first to demonstrate intraspecific variation in natural populations as well as variation in SI over an individual's lifespan.
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Affiliation(s)
- Chelsea Pretz
- Department of Ecology and Evolutionary Biology, University of Colorado, 1900 Pleasant Street, Boulder, CO 80309, USA
- Corresponding author’s e-mail address:
| | - Stacey D Smith
- Department of Ecology and Evolutionary Biology, University of Colorado, 1900 Pleasant Street, Boulder, CO 80309, USA
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4
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Hu J, Xu Q, Liu C, Liu B, Deng C, Chen C, Wei Z, Ahmad MH, Peng K, Wen H, Chen X, Chen P, Larkin RM, Ye J, Deng X, Chai L. Downregulated expression of S 2-RNase attenuates self-incompatibility in "Guiyou No. 1" pummelo. HORTICULTURE RESEARCH 2021; 8:199. [PMID: 34465762 PMCID: PMC8408199 DOI: 10.1038/s41438-021-00634-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 05/27/2021] [Accepted: 06/01/2021] [Indexed: 06/13/2023]
Abstract
Self-incompatibility (SI) substantially restricts the yield and quality of citrus. Therefore, breeding and analyzing self-compatible germplasm is of great theoretical and practical significance for citrus. Here, we focus on the mechanism of a self-compatibility mutation in 'Guiyou No. 1' pummelo (Citrus maxima), which is a spontaneous mutant of 'Shatian' pummelo (Citrus maxima, self-incompatibility). The rate of fruit set and the growth of pollen tubes in the pistil confirmed that a spontaneous mutation in the pistil is responsible for the self-compatibility of 'Guiyou No. 1'. Segregation ratios of the S genotype in F1 progeny, expression analysis, and western blotting validated that the reduced levels of S2-RNase mRNA contribute to the loss of SI in 'Guiyou No. 1'. Furthermore, we report a phased assembly of the 'Guiyou No. 1' pummelo genome and obtained two complete and well-annotated S haplotypes. Coupled with an analysis of SV variations, methylation levels, and gene expression, we identified a candidate gene (CgHB40), that may influence the regulation of the S2-RNase promoter. Our data provide evidence that a mutation that affects the pistil led to the loss of SI in 'Guiyou No. 1' by influencing a poorly understood mechanism that affects transcriptional regulation. This work significantly advances our understanding of the genetic basis of the SI system in citrus and provides information on the regulation of S-RNase genes.
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Affiliation(s)
- Jianbing Hu
- Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China
| | - Qiang Xu
- Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China
| | - Chenchen Liu
- Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China
| | - Binghao Liu
- Guangxi Engineering Research Center of Citrus Breeding and Culture, Guangxi Academy of Specialty Crops, Guilin, 541004, People's Republic of China
| | - Chongling Deng
- Guangxi Engineering Research Center of Citrus Breeding and Culture, Guangxi Academy of Specialty Crops, Guilin, 541004, People's Republic of China
| | - Chuanwu Chen
- Guangxi Engineering Research Center of Citrus Breeding and Culture, Guangxi Academy of Specialty Crops, Guilin, 541004, People's Republic of China
| | - Zhuangmin Wei
- Guangxi Subtropical Crops Research Institute, Nanning, 530001, People's Republic of China
| | - Muhammad Husnain Ahmad
- Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China
| | - Kang Peng
- Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China
| | - Hao Wen
- Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China
| | - Xiangling Chen
- Horticulture Research Institute, Guangxi Academy of Agriculture Sciences, Nanning Investigation & Experiment Station of South Subtropical Fruit Trees, Ministry of Agriculture, Nanning, 530007, Guangxi, People's Republic of China
| | - Peng Chen
- Horticultural Institute, Hunan Academy of Agricultural Sciences, Changsha, 410125, People's Republic of China
| | - Robert M Larkin
- Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China
| | - Junli Ye
- Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China
| | - Xiuxin Deng
- Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China
| | - Lijun Chai
- Key Laboratory of Horticultural Plant Biology, Ministry of Education, College of Horticulture and Forestry Sciences, Huazhong Agricultural University, Wuhan, 430070, People's Republic of China.
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Ramanauskas K, Igić B. RNase-based self-incompatibility in cacti. THE NEW PHYTOLOGIST 2021; 231:2039-2049. [PMID: 34101188 DOI: 10.1111/nph.17541] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Accepted: 05/28/2021] [Indexed: 06/12/2023]
Abstract
Approximately one-half of all flowering plants express genetically based physiological mechanisms that prevent self-fertilisation. One such mechanism, termed RNase-based self-incompatibility, employs ribonucleases as the pistil component. Although it is widespread, it has only been characterised in a handful of distantly related families, partly due to the difficulties presented by life history traits of many plants, which complicate genetic research. Many species in the cactus family are known to express self-incompatibility but the underlying mechanisms remain unknown. We demonstrate the utility of a candidate-based RNA-seq approach, combined with some unusual features of self-incompatibility-causing genes, which we use to uncover the genetic basis of the underlying mechanisms. Specifically, we assembled transcriptomes from Schlumbergera truncata (crab cactus or false Christmas cactus), and interrogated them for tissue-specific expression of candidate genes, structural characteristics, correlation with expressed phenotype(s), and phylogenetic placement. The results were consistent with operation of the RNase-based self-incompatibility mechanism in Cactaceae. The finding yields additional evidence that the ancestor of nearly all eudicots possessed RNase-based self-incompatibility, as well as a clear path to better conservation practices for one of the most charismatic plant families.
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Affiliation(s)
- Karolis Ramanauskas
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Il, 60607, USA
| | - Boris Igić
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, Il, 60607, USA
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6
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Glémin S. Balancing selection in self-fertilizing populations. Evolution 2021; 75:1011-1029. [PMID: 33675041 DOI: 10.1111/evo.14194] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Accepted: 01/17/2021] [Indexed: 11/30/2022]
Abstract
Self-fertilization commonly occurs in hermaphroditic species, either occasionally or as the main reproductive mode. It strongly affects the genetic functioning of a population by increasing homozygosity and genetic drift and reducing the effectiveness of recombination. Balancing selection is a form of selection that maintains polymorphism, which has been extensively studied in outcrossing species. Yet, despite recent developments, the analysis of balancing selection in partially selfing species is limited to specific cases and a general treatment is still lacking. In particular, it is unclear whether selfing globally reduced the efficacy of balancing selection as in the well-known case of overdominance. I provide a unifying framework, quantify how selfing affects the maintenance of polymorphism and the efficacy of the different form of balancing selection, and show that they can be classified into two main categories: overdominance-like selection (including true overdominance, selection variable in space and time, and antagonistic selection), which is strongly affected by selfing, and negative frequency dependent selection, which is barely affected by selfing, even at multiple loci. I also provide simple analytical results for all cases under the assumption of weak selection. This framework provides theoretical background to analyze the genomic signature of balancing selection in partially selfing species. It also sheds new light on the evolution of selfing species, including the evolution of selfing syndrome, the interaction with pathogens, and the evolutionary fate of selfing lineages.
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Affiliation(s)
- Sylvain Glémin
- CNRS, ECOBIO (Ecosystèmes, biodiversité, évolution), University of Rennes 1, UMR 6553, Rennes, France.,Department of Ecology and Genetics, Evolutionary Biology Centre, Uppsala University, Uppsala, 752 36, Sweden
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7
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Moyle LC, Wu M, Gibson MJS. Reproductive Proteins Evolve Faster Than Non-reproductive Proteins Among Solanum Species. FRONTIERS IN PLANT SCIENCE 2021; 12:635990. [PMID: 33912206 PMCID: PMC8072272 DOI: 10.3389/fpls.2021.635990] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 03/01/2021] [Indexed: 05/13/2023]
Abstract
Elevated rates of evolution in reproductive proteins are commonly observed in animal species, and are thought to be driven by the action of sexual selection and sexual conflict acting specifically on reproductive traits. Whether similar patterns are broadly observed in other biological groups is equivocal. Here, we examine patterns of protein divergence among wild tomato species (Solanum section Lycopersicon), to understand forces shaping the evolution of reproductive genes in this diverse, rapidly evolving plant clade. By comparing rates of molecular evolution among loci expressed in reproductive and non-reproductive tissues, our aims were to test if: (a) reproductive-specific loci evolve more rapidly, on average, than non-reproductive loci; (b) 'male'-specific loci evolve at different rates than 'female'-specific loci; (c) genes expressed exclusively in gametophytic (haploid) tissue evolve differently from genes expressed in sporophytic (diploid) tissue or in both tissue types; and (d) mating system variation (a potential proxy for the expected strength of sexual selection and/or sexual conflict) affects patterns of protein evolution. We observed elevated evolutionary rates in reproductive proteins. However, this pattern was most evident for female- rather than male-specific loci, both broadly and for individual loci inferred to be positively selected. These elevated rates might be facilitated by greater tissue-specificity of reproductive proteins, as faster rates were also associated with more narrow expression domains. In contrast, we found little evidence that evolutionary rates are consistently different in loci experiencing haploid selection (gametophytic-exclusive loci), or in lineages with quantitatively different mating systems. Overall while reproductive protein evolution is generally elevated in this diverse plant group, some specific patterns of evolution are more complex than those reported in other (largely animal) systems, and include a more prominent role for female-specific loci among adaptively evolving genes.
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8
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Siopa C, Dias MC, Castro M, Loureiro J, Castro S. Is selfing a reproductive assurance promoting polyploid establishment? Reduced fitness, leaky self-incompatibility and lower inbreeding depression in neotetraploids. AMERICAN JOURNAL OF BOTANY 2020; 107:526-538. [PMID: 32144761 DOI: 10.1002/ajb2.1441] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Accepted: 01/14/2020] [Indexed: 06/10/2023]
Abstract
PREMISE Newly formed polyploids face significant obstacles to persistence and population establishment because of fitness costs of intercytotype mating. Selfing provides the opportunity to escape mate limitation, enabling production of new individuals and increasing the likelihood of fixation of new polyploid lineages. Still, association between self-compatibility and polyploidy is not always clear. We compared self-incompatibility and inbreeding depression in neotetraploids and their diploid progenitor to explore the direct effects of whole genome duplications on self-incompatibility and the implications of ploidy-driven changes for polyploid establishment. METHODS Outcross and self-pollinations were performed in diploids and synthetic neotetraploids of Jasione maritima var. maritima, and reproductive success was measured through fruit and seed production and seed germination. Self- and outcross offspring were grown under controlled conditions, and plant performance was measured through several fitness parameters. RESULTS Neotetraploids showed an overall lower performance than diploids. Reproductive success was negatively affected by selfing in both cytotypes. However, greater variation in the expression of self-incompatibility was observed in neotetraploids; additionally, developmental and physiological parameters were not affected by selfing on neotetraploids, with an overall similar fitness of outcrossed and selfed individuals, resulting in lower inbreeding depression indexes. CONCLUSIONS Neotetraploids might have benefited from selfing at initial stages after their formation. Genome duplications resulted in leaky self-incompatibility, enabling the production of offspring under minority cytotype disadvantage with similar fitness as outcrossed offspring. Our results support theoretical assumptions that selfing might be important for neopolyploid establishment, although changes in self-incompatibility might not be abrupt.
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Affiliation(s)
- Catarina Siopa
- Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, 3000-456, Coimbra, Portugal
| | - Maria C Dias
- Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, 3000-456, Coimbra, Portugal
| | - Mariana Castro
- Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, 3000-456, Coimbra, Portugal
| | - João Loureiro
- Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, 3000-456, Coimbra, Portugal
| | - Sílvia Castro
- Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, 3000-456, Coimbra, Portugal
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9
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Liang M, Cao Z, Zhu A, Liu Y, Tao M, Yang H, Xu Q, Wang S, Liu J, Li Y, Chen C, Xie Z, Deng C, Ye J, Guo W, Xu Q, Xia R, Larkin RM, Deng X, Bosch M, Franklin-Tong VE, Chai L. Evolution of self-compatibility by a mutant S m-RNase in citrus. NATURE PLANTS 2020; 6:131-142. [PMID: 32055045 PMCID: PMC7030955 DOI: 10.1038/s41477-020-0597-3] [Citation(s) in RCA: 54] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Accepted: 01/08/2020] [Indexed: 05/07/2023]
Abstract
Self-incompatibility (SI) is an important mechanism that prevents self-fertilization and inbreeding in flowering plants. The most widespread SI system utilizes S ribonucleases (S-RNases) and S-locus F-boxes (SLFs) as S determinants. In citrus, SI is ancestral, and Citrus maxima (pummelo) is self-incompatible, while Citrus reticulata (mandarin) and its hybrids are self-compatible (SC). Here, we identify nine highly polymorphic pistil-specific, developmentally expressed S-RNases from pummelo that segregate with S haplotypes in a gametophytic manner and cluster with authentic S-RNases. We provide evidence that these S-RNases function as the female S determinants in citrus. Moreover, we show that each S-RNase is linked to approximately nine SLFs. In an analysis of 117 citrus SLF and SFL-like (SLFL) genes, we reveal that they cluster into 12 types and that the S-RNases and intra-haplotypic SLF and SLFL genes co-evolved. Our data support the notion that citrus have a S locus comprising a S-RNase and several SLFs that fit the non-self-recognition model. We identify a predominant single nucleotide mutation, Sm-RNase, in SC citrus, which provides a 'natural' loss of function. We show that SI-SC transitions due to the Sm-RNase initially arose in mandarin, spreading to its hybrids and became fixed. Identification of an evolutionarily distant new genus utilizing the S-RNase-based SI system, >100 million years separated from the nearest S-RNase family, is a milestone for evolutionary comparative studies.
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Affiliation(s)
- Mei Liang
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
- Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, USA
| | - Zonghong Cao
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Andan Zhu
- Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, P. R. China
| | - Yuanlong Liu
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, South China Agricultural University, Guangzhou, P. R. China
| | - Mengqin Tao
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Huayan Yang
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Qiang Xu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Shaohua Wang
- Institute of Tropical and Subtropical Cash Crops, Yunnan Academy of Agricultural Sciences, Kunming, P. R. China
| | - Junjie Liu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Yongping Li
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Chuanwu Chen
- Guangxi Key Laboratory of Citrus Biology, Guangxi Academy of Specialty Crops, Guilin, P. R. China
| | - Zongzhou Xie
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Chongling Deng
- Guangxi Key Laboratory of Citrus Biology, Guangxi Academy of Specialty Crops, Guilin, P. R. China
| | - Junli Ye
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Wenwu Guo
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Qiang Xu
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Rui Xia
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, South China Agricultural University, Guangzhou, P. R. China
| | - Robert M Larkin
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Xiuxin Deng
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China
| | - Maurice Bosch
- Institute of Biological, Environmental and Rural Sciences (IBERS), Aberystwyth University, Plas Gogerddan, Aberystwyth, UK
| | - Vernonica E Franklin-Tong
- School of Biosciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, UK
| | - Lijun Chai
- Key Laboratory of Horticultural Plant Biology (Ministry of Education), Huazhong Agricultural University, Wuhan, P. R. China.
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Zenil-Ferguson R, Burleigh JG, Freyman WA, Igić B, Mayrose I, Goldberg EE. Interaction among ploidy, breeding system and lineage diversification. THE NEW PHYTOLOGIST 2019; 224:1252-1265. [PMID: 31617595 DOI: 10.1111/nph.16184] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2019] [Accepted: 08/14/2019] [Indexed: 05/28/2023]
Abstract
If particular traits consistently affect rates of speciation and extinction, broad macroevolutionary patterns can be interpreted as consequences of selection at high levels of the biological hierarchy. Identifying traits associated with diversification rates is difficult because of the wide variety of characters under consideration and the statistical challenges of testing for associations from comparative phylogenetic data. Ploidy (diploid vs polyploid states) and breeding system (self-incompatible vs self-compatible states) are both thought to be drivers of differential diversification in angiosperms. We fit 29 diversification models to extensive trait and phylogenetic data in Solanaceae and investigate how speciation and extinction rate differences are associated with ploidy, breeding system, and the interaction between these traits. We show that diversification patterns in Solanaceae are better explained by breeding system and an additional unobserved factor, rather than by ploidy. We also find that the most common evolutionary pathway to polyploidy in Solanaceae occurs via direct breakdown of self-incompatibility by whole genome duplication, rather than indirectly via breakdown followed by polyploidization. Comparing multiple stochastic diversification models that include complex trait interactions alongside hidden states enhances our understanding of the macroevolutionary patterns in plant phylogenies.
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Affiliation(s)
| | - J Gordon Burleigh
- Department of Biology, University of Florida, Gainesville, FL, 32611, USA
| | - William A Freyman
- Department of Ecology, Evolution and Behavior, University of Minnesota, Saint Paul, MN, 55108, USA
| | - Boris Igić
- Department of Biological Sciences, University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Itay Mayrose
- School of Plant Sciences and Food Security, Tel Aviv University, Tel Aviv, 6997801, Israel
| | - Emma E Goldberg
- Department of Ecology, Evolution and Behavior, University of Minnesota, Saint Paul, MN, 55108, USA
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Wu M, Kostyun JL, Moyle LC. Genome Sequence of Jaltomata Addresses Rapid Reproductive Trait Evolution and Enhances Comparative Genomics in the Hyper-Diverse Solanaceae. Genome Biol Evol 2019; 11:335-349. [PMID: 30608583 PMCID: PMC6368146 DOI: 10.1093/gbe/evy274] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/16/2018] [Indexed: 12/11/2022] Open
Abstract
Within the economically important plant family Solanaceae, Jaltomata is a rapidly evolving genus that has extensive diversity in flower size and shape, as well as fruit and nectar color, among its ∼80 species. Here, we report the whole-genome sequencing, assembly, and annotation, of one representative species (Jaltomata sinuosa) from this genus. Combining PacBio long reads (25×) and Illumina short reads (148×) achieved an assembly of ∼1.45 Gb, spanning ∼96% of the estimated genome. Ninety-six percent of curated single-copy orthologs in plants were detected in the assembly, supporting a high level of completeness of the genome. Similar to other Solanaceous species, repetitive elements made up a large fraction (∼80%) of the genome, with the most recently active element, Gypsy, expanding across the genome in the last 1–2 Myr. Computational gene prediction, in conjunction with a merged transcriptome data set from 11 tissues, identified 34,725 protein-coding genes. Comparative phylogenetic analyses with six other sequenced Solanaceae species determined that Jaltomata is most likely sister to Solanum, although a large fraction of gene trees supported a conflicting bipartition consistent with substantial introgression between Jaltomata and Capsicum after these species split. We also identified gene family dynamics specific to Jaltomata, including expansion of gene families potentially involved in novel reproductive trait development, and loss of gene families that accompanied the loss of self-incompatibility. This high-quality genome will facilitate studies of phenotypic diversification in this rapidly radiating group and provide a new point of comparison for broader analyses of genomic evolution across the Solanaceae.
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Affiliation(s)
- Meng Wu
- Department of Biology, Indiana University Bloomington
| | - Jamie L Kostyun
- Department of Biology, Indiana University Bloomington.,Department of Plant Biology, University of Vermont
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12
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Sutherland BL, Galloway LF. Effects of glaciation and whole genome duplication on the distribution of the Campanula rotundifolia polyploid complex. AMERICAN JOURNAL OF BOTANY 2018; 105:1760-1770. [PMID: 30312483 DOI: 10.1002/ajb2.1162] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2018] [Accepted: 06/26/2018] [Indexed: 06/08/2023]
Abstract
PREMISE OF THE STUDY Both intrinsic and extrinsic factors contribute to a species distribution. Among plants, the extrinsic effects of glaciation and intrinsic effects of whole genome duplication are powerful drivers of biogeographical patterns, but the interplay of these factors is poorly understood. Here, we investigate the roles glaciation and whole-genome duplication have played in the evolution of the widespread polyploid complex Campanula rotundifolia. METHODS We assessed the cytotype of 37 populations that spanned the geographic and cytotypic range of the C. rotundifolia complex. We constructed a chloroplast phylogeny for these populations and used RAD-seq to create nuclear phylogenies and networks for a subset of 23 populations; and estimated divergence times of major clades using Bayesian estimation of substitution rates. KEY RESULTS Campanula rotundifolia originated in south-central Europe and underwent range expansion throughout much of Europe and North America. Multiple genome duplications have occurred in C. rotundifolia-at least two tetraploid and three hexaploid formations. CONCLUSIONS Nuclear and chloroplast phylogenies are largely congruent with a history of populations surviving glacial maxima in known Pleistocene refugia in Europe and North America. Divergent European clades are consistent with two disjunct glacial refugia within Europe. North America was colonized by hexaploids derived from Western European lineages. A glacial refugium in Midwestern North America likely facilitated post-glacial recolonization of North America and limited genetic divergence. These results implicate both glaciation and whole-genome duplication as contributing factors to the extant biogeography of C. rotundifolia.
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Affiliation(s)
- Brittany L Sutherland
- Department of Biology, University of Virginia, Charlottesville, VA, 22904-4328, USA
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721
| | - Laura F Galloway
- Department of Biology, University of Virginia, Charlottesville, VA, 22904-4328, USA
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13
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Koontz SM, Weekley CW, Haller Crate SJ, Menges ES. Patterns of chasmogamy and cleistogamy, a mixed-mating strategy in an endangered perennial. AOB PLANTS 2017; 9:plx059. [PMID: 29308127 PMCID: PMC5751043 DOI: 10.1093/aobpla/plx059] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2017] [Accepted: 10/30/2017] [Indexed: 05/24/2023]
Abstract
Cleistogamy (CL) in angiosperms historically has been understudied; however, its co-occurrence with chasmogamy (CH) across many plant species suggests a fitness advantage to maintaining this mixed-mating strategy. Maintenance of mixed-mating has been attributed to reproductive assurance, resource allocation or genetic trade-offs. Our goals were to explore patterns of CH and CL, quantify reproductive contributions measured by fruit production and determine how CL is maintained in the endangered perennial Polygala lewtonii. This species exhibits CH and both above-ground cleistogamy (CL-AG) and below-ground cleistogamy (CL-BG). In monthly censuses from 2008 to 2012, we documented flowering patterns by counting CH flowering stems, CL-AG fruits and CL-BG rhizomes per plant. Monitoring of buds on CH flowering stems in 2004 provided an estimate of CH fruits per plant. Plant excavations in 2005 of CL-BG rhizomes provided an estimate of CL-BG fruits per plant. Floral morphs were temporally separated with CH flowers observed from January to May and CL flowers from June to February. Overall, 17.5 % of plants flowered; most plants expressed CH first in spring months (63.4 %) and the rest initiated CL-AG in fall months. Reproductive output was dominated by CH (median 26 fruits) compared to combined CL (median 3.5 fruits). Annual reproductive effort of CL-AG was positively correlated with plant age while CH had no relation. Our research shows CH as the dominant form of reproductive effort with most individuals expressing CH and through greater reproductive contributions. CL appears limited by plant size or resources based on the positive relationship with plant age. CL dependency on resource availability is common in other species found in dry or low-quality habitats; however, CL contributions in this species are comparatively low. This raises more questions related to energy requirements of both floral morphs, how this affects the production of viable progeny and why CL persists.
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Affiliation(s)
| | - Carl W Weekley
- The Plant Ecology Program, Archbold Biological Station, FL, USA
| | - Sarah J Haller Crate
- Longleaf Program Coordinator, North Carolina Forest Service, North Carolina Department of Agriculture and Consumer Services, NC, USA
| | - Eric S Menges
- The Plant Ecology Program, Archbold Biological Station, FL, USA
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14
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Two Loci Contribute Epistastically to Heterospecific Pollen Rejection, a Postmating Isolating Barrier Between Species. G3-GENES GENOMES GENETICS 2017; 7:2151-2159. [PMID: 28512086 PMCID: PMC5499124 DOI: 10.1534/g3.117.041673] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Recognition and rejection of heterospecific male gametes occurs in a broad range of taxa, although the complexity of mechanisms underlying these components of postmating cryptic female choice is poorly understood. In plants, the arena for postmating interactions is the female reproductive tract (pistil), within which heterospecific pollen tube growth can be arrested via active molecular recognition and rejection. Unilateral incompatibility (UI) is one such postmating barrier in which pollen arrest occurs in only one direction of an interspecific cross. We investigated the genetic basis of pistil-side UI between Solanum species, with the specific goal of understanding the role and magnitude of epistasis between UI QTL. Using heterospecific introgression lines (ILs) between Solanum pennellii and S. lycopersicum, we assessed the individual and pairwise effects of three chromosomal regions (ui1.1, ui3.1, and ui12.1) previously associated with interspecific UI among Solanum species. Specifically, we generated double introgression (‘pyramided’) genotypes that combined ui12.1 with each of ui1.1 and ui3.1, and assessed the strength of UI pollen rejection in the pyramided lines, compared to single introgression genotypes. We found that none of the three QTL individually showed UI rejection phenotypes, but lines combining ui3.1 and ui12.1 showed significant pistil-side pollen rejection. Furthermore, double ILs (DILs) that combined different chromosomal regions overlapping ui3.1 differed significantly in their rate of UI, consistent with at least two genetic factors on chromosome three contributing quantitatively to interspecific pollen rejection. Together, our data indicate that loci on both chromosomes 3 and 12 are jointly required for the expression of UI between S. pennellii and S. lycopersicum, suggesting that coordinated molecular interactions among a relatively few loci underlie the expression of this postmating prezygotic barrier. In addition, in conjunction with previous data, at least one of these loci appears to also contribute to conspecific self-incompatibility (SI), consistent with a partially shared genetic basis between inter- and intraspecific mechanisms of postmating prezygotic female choice.
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15
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Glick L, Sabath N, Ashman TL, Goldberg E, Mayrose I. Polyploidy and sexual system in angiosperms: Is there an association? AMERICAN JOURNAL OF BOTANY 2016; 103:1223-1235. [PMID: 27352832 DOI: 10.3732/ajb.1500424] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 04/19/2016] [Indexed: 06/06/2023]
Abstract
PREMISE OF THE STUDY Flowering plants display a variety of sexual systems, ranging from complete cosexuality (hermaphroditism) to separate-sexed individuals (dioecy). While dioecy is relatively rare, it has evolved many times and is present in many plant families. Transitions in sexual systems are hypothesized to be affected by large genomic events such as whole-genome duplication, or polyploidy, and several models have been proposed to explain the observed patterns of association. METHODS In this study, we assessed the association between ploidy and sexual system (separate or combined sexes). To this end, we assembled a database of ploidy levels and sexual systems for ∼1000 species, spanning 18 genera and 15 families. We applied several phylogenetic comparative approaches, including Pagel's coevolutionary framework and sister clade analyses, for detecting correlations between ploidy level and sexual system. KEY RESULTS Our results indicate a broad association between polyploidy and sexual system dimorphism, with low evolutionary stability of the diploid-dioecious condition observed in several clades. A detailed examination of the clades exhibiting this correlation reveals that it is underlain by various patterns of transition rate asymmetry. CONCLUSIONS We conclude that the long-hypothesized connection between ploidy and sexual system holds in some clades, although it may well be affected by factors that differ from clade to clade. Our results further demonstrate that to better understand the evolutionary processes involved, more sophisticated methods and extensive and detailed data sets are required for both broad and focused inquiry.
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Affiliation(s)
- Lior Glick
- Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv, Israel
| | - Niv Sabath
- Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv, Israel
| | - Tia-Lynn Ashman
- Department of Biological Sciences University of Pittsburgh, Pittsburgh, Pennsylvania 15260 USA
| | - Emma Goldberg
- Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, Minnesota 55108-6097 USA
| | - Itay Mayrose
- Department of Molecular Biology and Ecology of Plants, Tel Aviv University, Tel Aviv, Israel
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16
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Miller JS, Kamath A, Husband BC, Levin RA. Correlated polymorphism in cytotype and sexual system within a monophyletic species, Lycium californicum. ANNALS OF BOTANY 2016; 117:307-17. [PMID: 26546375 PMCID: PMC4724043 DOI: 10.1093/aob/mcv167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2015] [Revised: 07/30/2015] [Accepted: 09/18/2015] [Indexed: 05/08/2023]
Abstract
BACKGROUND AND AIMS Polyploidy has important effects on reproductive systems in plants and has been implicated in the evolution of dimorphic sexual systems. In particular, higher ploidy is associated with gender dimorphism across Lycium species (Solanaceae) and across populations within the species Lycium californicum. Previous research on the association of cytotype and sexual system within L. californicum sampled a limited portion of the species range, and did not investigate evolutionary transitions between sexual systems. Lycium californicum occurs in arid regions on offshore islands and mainland regions in the south-western United States and Mexico, motivating a more comprehensive analysis of intraspecific variation in sexual system and cytotype across the full range of this species. METHODS Sexual system (dimorphic vs. cosexual) was determined for 34 populations across the geographical range of L. californicum using field observations of pollen production, and was confirmed using morphological measurements and among-plant correlations of primary sexual traits. Ploidy was inferred using flow cytometry in 28 populations. DNA sequence data from four plastid and two nuclear regions were used to reconstruct relationships among populations and to map transitions in sexual system and ploidy. KEY RESULTS Lycium californicum is monophyletic, ancestrally diploid and cosexual, and the association of gender dimorphism and polyploidy appears to have two evolutionary origins in this species. Compared with cosexual populations, dimorphic populations had bimodal anther size distributions, negative correlations between male and female floral traits, and larger coefficients of variation for primary sexual traits. Flow cytometry confirmed tetraploidy in dimorphic populations, whereas cosexual populations were diploid. CONCLUSIONS Tetraploidy and gender dimorphism are perfectly correlated in L. californicum, and the distribution of tetraploid-dimorphic populations is restricted to populations in Arizona and the Baja California peninsula. The analysis suggests that tetraploidy and dimorphism likely established in Baja California and may have evolved multiple times.
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Affiliation(s)
- Jill S Miller
- Department of Biology, Amherst College, Amherst, MA 01002 USA,
| | - Ambika Kamath
- Department of Biology, Amherst College, Amherst, MA 01002 USA, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA and
| | - Brian C Husband
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, N1G 2W1 Canada
| | - Rachel A Levin
- Department of Biology, Amherst College, Amherst, MA 01002 USA
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17
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Gervais C, Awad DA, Roze D, Castric V, Billiard S. GENETIC ARCHITECTURE OF INBREEDING DEPRESSION AND THE MAINTENANCE OF GAMETOPHYTIC SELF-INCOMPATIBILITY. Evolution 2014; 68:3317-24. [DOI: 10.1111/evo.12495] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2014] [Accepted: 07/02/2014] [Indexed: 11/28/2022]
Affiliation(s)
- Camille Gervais
- UMI 3614; Evolutionary Biology and Ecology of Algae; CNRS; 29680 Roscoff France
- Sorbonne Universités; UPMC University Paris 06 29680 Roscoff France
| | - Diala Abu Awad
- Laboratoire de Génétique et Evolution des Populations Végétales; UMR CNRS 8198; Université Lille 1 - Sciences et Technologies; 59655 Villeneuve d'Ascq France
| | - Denis Roze
- UMI 3614; Evolutionary Biology and Ecology of Algae; CNRS; 29680 Roscoff France
- Sorbonne Universités; UPMC University Paris 06 29680 Roscoff France
| | - Vincent Castric
- Laboratoire de Génétique et Evolution des Populations Végétales; UMR CNRS 8198; Université Lille 1 - Sciences et Technologies; 59655 Villeneuve d'Ascq France
| | - Sylvain Billiard
- Laboratoire de Génétique et Evolution des Populations Végétales; UMR CNRS 8198; Université Lille 1 - Sciences et Technologies; 59655 Villeneuve d'Ascq France
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18
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Vosters SL, Jewell CP, Sherman NA, Einterz F, Blackman BK, Moyle LC. The timing of molecular and morphological changes underlying reproductive transitions in wild tomatoes (Solanum sect. Lycopersicon). Mol Ecol 2014; 23:1965-78. [PMID: 24589309 DOI: 10.1111/mec.12708] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2013] [Revised: 02/01/2014] [Accepted: 02/04/2014] [Indexed: 01/08/2023]
Abstract
Molecular mechanisms underlying the transition from genetic self-incompatibility to self-compatibility are well documented, but the evolution of other reproductive trait changes that accompany shifts in reproductive strategy (mating system) remains comparatively under-investigated. A notable exception is the transition from exserted styles to styles with recessed positions relative to the anthers in wild tomatoes (Solanum Section Lycopersicon). This phenotypic change has been previously attributed to a specific mutation in the promoter of a gene that influences style length (style2.1); however, whether this specific regulatory mutation arose concurrently with the transition from long to short styles, and whether it is causally responsible for this phenotypic transition, has been poorly investigated across this group. To address this gap, we assessed 74 accessions (populations) from 13 species for quantitative genetic variation in floral and reproductive traits as well as the presence/absence of deletions at two different locations (StyleD1 and StyleD2) within the regulatory region upstream of style2.1. We confirmed that the putatively causal deletion variant (a 450-bp deletion at StyleD1) arose within self-compatible lineages. However, the variation and history of both StyleD1 and StyleD2 was more complex than previously inferred. In particular, although StyleD1 was statistically associated with differences in style length and stigma exsertion across all species, we found no evidence for this association within two species polymorphic for the StyleD1 mutation. We conclude that the previous association detected between phenotypic and molecular differences is most likely due to a phylogenetic association rather than a causal mechanistic relationship. Phenotypic variation in style length must therefore be due to other unexamined linked variants in the style2.1 regulatory region.
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Affiliation(s)
- S L Vosters
- Department of Biology, Indiana University, Bloomington, 47405, IN, USA
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19
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Stone JL, VanWyk EJ, Hale JR. Transmission advantage favors selfing allele in experimental populations of self-incompatible Witheringia solanacea (solanaceae). Evolution 2014; 68:1845-55. [PMID: 24713065 DOI: 10.1111/evo.12419] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2013] [Accepted: 03/18/2014] [Indexed: 11/30/2022]
Abstract
The evolution of self-fertilization is one of the most commonly traversed transitions in flowering plants, with profound implications for population genetic structure and evolutionary potential. We investigated factors influencing this transition using Witheringia solanacea, a predominantly self-incompatible (SI) species within which self-compatible (SC) genotypes have been identified. We showed that self-compatibility in this species segregates with variation at the S-locus as inherited by plants in F1 and F2 generations. To examine reproductive assurance and the transmission advantage of selfing, we placed SC and SI genotypes in genetically replicated gardens and monitored male and female reproductive success, as well as selfing rates of SC plants. Self-compatibility did not lead to increased fruit or seed set, even under conditions of pollinator scarcity, and the realized selfing rate of SC plants was less than 10%. SC plants had higher fruit abortion rates, consistent with previous evidence showing strong inbreeding depression at the embryonic stage. Although the selfing allele did not provide reproductive assurance under observed conditions, it also did not cause pollen discounting, so the transmission advantage of selfing should promote its spread. Given observed numbers of S-alleles and selfing rates, self-compatibility should spread even under conditions of exceedingly high initial inbreeding depression.
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Affiliation(s)
- Judy L Stone
- Department of Biology, Colby College, Waterville, Maine, 04901.
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20
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Dobeš C, Milosevic A, Prohaska D, Scheffknecht S, Sharbel TF, Hülber K. Reproductive differentiation into sexual and apomictic polyploid cytotypes in Potentilla puberula (Potentilleae, Rosaceae). ANNALS OF BOTANY 2013; 112:1159-68. [PMID: 23960045 PMCID: PMC3783232 DOI: 10.1093/aob/mct167] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Accepted: 06/06/2013] [Indexed: 05/05/2023]
Abstract
BACKGROUND AND AIMS Intraspecific reproductive differentiation into sexual and apomictic cytotypes of differing ploidy is a common phenomenon. However, mechanisms enabling the maintenance of both reproductive modes and integrity of cytotypes in sympatry are as yet poorly understood. This study examined the association of sexual and apomictic seed formation with ploidy as well as gene flow towards sexuals within populations of purely polyploid Potentilla puberula. METHODS The study is based on 22 populations representing various combinations of five polyploid cytotypes (tetraploid-octoploid) from East Tyrol, Austria. Embryo ploidy and the endosperm/embryo ploidy ratio obtained by a flow cytometric seed screen were used to infer reproductive modes of seed formation and to calculate the male and female genomic contributions to the embryo and endosperm. Self-incompatibility (SI) patterns were assessed and a new indirect approach was used to test for the occurrence of intercytotype matings based on the variation in the male genomic contribution to sexually derived embryos on the level of developed seed. KEY RESULTS Tetraploids formed seeds almost exclusively via sexual reproduction, whereas penta- to octoploids were preferentially apomictic. Non-random distribution of reproductive modes within maternal plants further revealed a tendency to separate the sexual from the apomictic mode among individuals. Self-incompatibility of sexuals indicated functionality of the gametophytic SI system despite tetraploidy of the nuclear genome. We found no indication for significant cross-fertilization of tetraploids by the high polyploids. CONCLUSIONS The study revealed a rare example of intraspecific differentiation into sexual and apomictic cytotypes at the polyploid level. The integrity of the sexual tetraploids was maintained due to reproductive isolation from the apomictic higher polyploids. Functionality of the gametophytic SI system suggested that the tetraploids are functional diploids.
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Key Words
- Apomixis, endosperm, European Alps, FCSS, flow cytometry, pollen, polyploidy, Potentilla puberula, reproductive isolation, Rosaceae, sexual reproduction
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Affiliation(s)
- Ch. Dobeš
- Department of Pharmacognosy, Pharmacobotany, University of Vienna,
Althanstrasse 14, 1090 Vienna, Austria
| | - A. Milosevic
- Department of Pharmacognosy, Pharmacobotany, University of Vienna,
Althanstrasse 14, 1090 Vienna, Austria
| | - D. Prohaska
- Department of Pharmacognosy, Pharmacobotany, University of Vienna,
Althanstrasse 14, 1090 Vienna, Austria
| | - S. Scheffknecht
- Department of Pharmacognosy, Pharmacobotany, University of Vienna,
Althanstrasse 14, 1090 Vienna, Austria
| | - T. F. Sharbel
- Apomixis Research Group, Leibniz-Institute for plant genetics and crop
research (IPK), Corrensstrasse 3, D-06466 Gatersleben, Germany
| | - K. Hülber
- Department of Conservation Biology, Vegetation Ecology and Landscape
Ecology, University of Vienna, Rennweg 14, 1030 Vienna, Austria
- Vienna Institute for Nature Conservation & Analyses, Giessergasse
6/7, 1090 Vienna, Austria
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21
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Iles WJD, Rudall PJ, Sokoloff DD, Remizowa MV, Macfarlane TD, Logacheva MD, Graham SW. Molecular phylogenetics of Hydatellaceae (Nymphaeales): sexual-system homoplasy and a new sectional classification. AMERICAN JOURNAL OF BOTANY 2012; 99:663-676. [PMID: 22473977 DOI: 10.3732/ajb.1100524] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
PREMISE OF THE STUDY Species relationships are unknown in Hydatellaceae, a small family of dwarf aquatics related to water lilies that arose near the base of angiosperm phylogeny. Here we use molecular evidence to infer a species tree for the family and apply this to reconstructing major transitions in morphology and sexual system in this early branch of angiosperms. METHODS We assembled plastid (atpB, matK, ndhF, rbcL) and nuclear (ribosomal ITS) data for 50 samples (including outgroups) and estimated a species tree for Hydatellaceae using a Bayesian multispecies coalescent approach. We reconstructed the evolution of several morphological characters, then tested for associations between sexual system and reproductive morphology using phylogenetic ANOVA. KEY RESULTS Dioecious species of Hydatellaceae have significantly greater stamen number and anther length than do cosexual species, suggesting changes in male function. The perennial habit that defines one subclade likely represents a reversion from annuality. Species relationships do not fall along traditional morphological divisions, but new sections proposed here are supported by fruit and seed synapomorphies. The earliest split in the family is reflected in geography and climate (i.e., tropical vs. subtropical/temperate clades). We found limited evidence of incongruence between plastid and nuclear trees, with one exception involving gene-tree nonmonophyly for two close relatives (Trithuria submersa, T. bibracteata). CONCLUSIONS While the direction of sexual-system evolution is ambiguous, transitions are significantly associated with changes in involucral phyllome length and proxies of pollen production. We propose a new sectional circumscription based on fruit, seed, and DNA evidence.
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Affiliation(s)
- William J D Iles
- UBC Botanical Garden & Centre for Plant Research, and Department of Botany, 6270 University Boulevard, University of British Columbia, Vancouver, BC, Canada.
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Muraya MM, Mutegi E, Geiger HH, de Villiers SM, Sagnard F, Kanyenji BM, Kiambi D, Parzies HK. Wild sorghum from different eco-geographic regions of Kenya display a mixed mating system. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 2011; 122:1631-9. [PMID: 21360157 DOI: 10.1007/s00122-011-1560-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2010] [Accepted: 02/12/2011] [Indexed: 05/14/2023]
Abstract
Knowledge of mating systems is required in order to understand the genetic composition and evolutionary potential of plant populations. Outcrossing in a population may co-vary with the ecological and historical factors influencing it. However, literature on the outcrossing rate is limited in terms of wild sorghum species coverage and eco-geographic reference. This study investigated the outcrossing rates in wild sorghum populations from different ecological conditions of Kenya. Twelve wild sorghum populations were collected in four sorghum growing regions. Twenty-four individuals per population were genotyped using six polymorphic simple sequence repeat (SSR) markers to compute their indirect equilibrium estimates of outcrossing rate as well as population structure. In addition, the 12 populations were planted in a field in a randomised block design with five replications. Their progeny (250 individuals per population) were genotyped with the six SSR markers to estimate multi-locus outcrossing rates. Equilibrium estimates of outcrossing rates ranged from 7.0 to 75.0%, while multi-locus outcrossing rates (t (m)) ranged from 8.9 to 70.0% with a mean of 49.7%, indicating that wild sorghum exhibits a mixed mating system. The wide range of estimated outcrossing rates in wild sorghum populations indicate that environmental conditions may exist under which fitness is favoured by outcrossing and others under which selfing is more advantageous. The genetic structure of the populations studied is concordant with that expected for a species displaying mixed mating system.
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Affiliation(s)
- Moses M Muraya
- Leibniz Institute of Plant Genetics and Crop Plant Research, Corrensstrasse 3, Gatersleben, Germany.
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Insights Gained From 50 Years of Studying the Evolution of Self-Compatibility in Leavenworthia (Brassicaceae). Evol Biol 2010. [DOI: 10.1007/s11692-010-9104-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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24
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Robertson K, Goldberg EE, Igić B. Comparative evidence for the correlated evolution of polyploidy and self-compatibility in Solanaceae. Evolution 2010; 65:139-55. [PMID: 20722729 DOI: 10.1111/j.1558-5646.2010.01099.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Breakdown of self-incompatibility occurs repeatedly in flowering plants with important evolutionary consequences. In plant families in which self-incompatibility is mediated by S-RNases, previous evidence suggests that polyploidy may often directly cause self-compatibility through the formation of diploid pollen grains. We use three approaches to examine relationships between self-incompatibility and ploidy. First, we test whether evolution of self-compatibility and polyploidy is correlated in the nightshade family (Solanaceae), and find the expected close association between polyploidy and self-compatibility. Second, we compare the rate of breakdown of self-incompatibility in the absence of polyploidy against the rate of breakdown that arises as a byproduct of polyploidization, and we find the former to be greater. Third, we apply a novel extension to these methods to show that the relative magnitudes of the macroevolutionary pathways leading to self-compatible polyploids are time dependent. Over small time intervals, the direct pathway from self-incompatible diploids is dominant, whereas the pathway through self-compatible diploids prevails over longer time scales. This pathway analysis is broadly applicable to models of character evolution in which sequential combinations of rates are compared. Finally, given the strong evidence for both irreversibility of the loss of self-incompatibility in the family and the significant association between self-compatibility and polyploidy, we argue that ancient polyploidy is highly unlikely to have occurred within the Solanaceae, contrary to previous claims based on genomic analyses.
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Affiliation(s)
- Kelly Robertson
- Department of Biological Sciences, 840 West Taylor St., M/C 067, University of Illinois at Chicago, Chicago, Illinois 60607, USA.
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25
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Busch JW, Herlihy CR, Gunn L, Werner WJ. Mixed mating in a recently derived self-compatible population of Leavenworthia alabamica (Brassicaceae). AMERICAN JOURNAL OF BOTANY 2010; 97:1005-1013. [PMID: 21622470 DOI: 10.3732/ajb.1000032] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
PREMISE OF THE STUDY A mixture of outcrossing and selfing is often observed in plant populations. Although mixed mating is ubiquitous, it has several potential evolutionary explanations. Mixed mating may be actively maintained by selection, passively determined by the pollination environment, or a transitional stage during the evolution of self-fertilization. • METHODS We studied patterns of self-compatibility and selfing rates in a population of Leavenworthia alabamica that recently lost self-incompatibility. We also experimentally tested whether natural selection against selfing at the pre- or postzygotic stage is sufficient to explain mixed mating in this population. • KEY RESULTS Visualizing pollen tube growth following self-pollination, we found that nearly all plants were fully self-compatible. Progeny array analysis revealed that the average selfing rate of the population was s = 0.523. The inbreeding coefficient in the parents (F = 0.539) exceeded the amount expected if the selfing rate (s) were constant [F(eq) = s/(2 - s)], indicating either population subdivision or higher selfing rates in the past. Inference of family-level selfing rates revealed substantial variation. Experiments found that self and outcross pollen fertilized nearly equal numbers of ovules in competition. Comparison of seed production following self- or cross-pollination failed to implicate early acting inbreeding depression as a factor maintaining mixed mating. • CONCLUSIONS The results of our experiments suggest that mixed mating is not maintained by selection against self-pollen or zygotes in this population. Mixed mating is most likely a byproduct of the pollination process but may also be a transitional stage during the evolution of higher selfing rates.
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Affiliation(s)
- Jeremiah W Busch
- School of Biological Sciences and the Center for Reproductive Biology, Washington State University, P.O. Box 644236, Pullman, Washington 99164 USA
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26
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Brennan AC, Hiscock SJ. Expression and inheritance of sporophytic self-incompatibility in synthetic allohexaploid Senecio cambrensis (Asteraceae). THE NEW PHYTOLOGIST 2010; 186:251-61. [PMID: 19895670 DOI: 10.1111/j.1469-8137.2009.03082.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Allopolyploid speciation is common in plants and is frequently associated with shifts from outcrossing, for example self-incompatibility, to inbreeding (i.e. selfing). Senecio cambrensis is a recently evolved allohexaploid species that formed following hybridization between diploid self-incompatible S. squalidus and tetraploid self-compatible S. vulgaris. Studies of reproduction in wild populations of S. cambrensis have concluded that it is self-compatible. Here, we investigated self-compatibility in synthetic lines of S. cambrensis generated via hybridization and colchicine-induced polyploidization and wild S. cambrensis using controlled crossing experiments. Synthetic F(1)S. cambrensis individuals were all self-compatible but, in F(2) and later generations, self-incompatible individuals were identified at frequencies of 6.7-9.2%. Self-incompatibility was also detected in wild sampled individuals at a frequency of 12.2%. The mechanism and genetics of self-incompatibility were tested in synthetic S. cambrensis and found to be similar to those of its paternal parent S. squalidus (i.e. sporophytic). These results show, for the first time, that functional sporophytic self-incompatibility can be inherited and expressed in allopolyploids as early as the second (F(2)) generation. Wild S. cambrensis should therefore be considered as possessing a mixed mating system with the potential for evolution towards either inbreeding or outcrossing.
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Hörandl E. The evolution of self-fertility in apomictic plants. SEXUAL PLANT REPRODUCTION 2010; 23:73-86. [PMID: 20165965 PMCID: PMC2854795 DOI: 10.1007/s00497-009-0122-3] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2009] [Accepted: 11/03/2009] [Indexed: 11/28/2022]
Abstract
Self-fertilization and apomixis have often been seen as alternative evolutionary strategies of flowering plants that are advantageous for colonization scenarios and in bottleneck situations. Both traits have multiple origins, but different genetic control mechanisms; possible connections between the two phenomena have long been overlooked. Most apomictic plants, however, need a fertilization of polar nuclei for normal seed development (pseudogamy). If self-pollen is used for this purpose, self-compatibility is a requirement for successful pollen tube growth. Apomictic lineages usually evolve from sexual self-incompatible outcrossing plants, but pseudogamous apomicts frequently show a breakdown of self-incompatibility. Two possible pathways may explain the evolution of SC: (1) Polyploidy not only may trigger gametophytic apomixis, but also may result in a partial breakdown of SI systems. (2) Alternatively, frequent pseudo self-compatibility (PSC) via aborted pollen may induce selfing of pseudogamous apomicts (mentor effects). Self-fertile pseudogamous genotypes will be selected for within mixed sexual-apomictic populations because of avoidance of interploidal crosses; in founder situations, SC provides reproductive assurance independent from pollinators and mating partners. SI pseudogamous genotypes will be selected against in mixed populations because of minority cytotype problems and high pollen discounting; in founder populations, SI reactions among clone mates will reduce seed set. Selection for SC genotypes will eliminate SI unless the apomict maintains a high genotypic diversity and thus a diversity of S-alleles within a population, or shifts to pollen-independent autonomous apomixis. The implications of a breakdown of SI in apomictic plants for evolutionary questions and for agricultural sciences are being discussed.
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Affiliation(s)
- Elvira Hörandl
- Department of Systematic and Evolutionary Botany, Faculty of Life Sciences, University of Vienna, Rennweg 14, 1030, Vienna, Austria.
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28
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Ferrer MM, Good-Avila SV, Montaña C, Domínguez CA, Eguiarte LE. Effect of variation in self-incompatibility on pollen limitation and inbreeding depression in Flourensia cernua (Asteraceae) scrubs of contrasting density. ANNALS OF BOTANY 2009; 103:1077-89. [PMID: 19218580 PMCID: PMC2707912 DOI: 10.1093/aob/mcp033] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2008] [Revised: 08/27/2008] [Accepted: 01/05/2009] [Indexed: 05/11/2023]
Abstract
BACKGROUND AND AIMS Selection may favour a partial or complete loss of self-incompatibility (SI) if it increases the reproductive output of individuals in the presence of low mate availability. The reproductive output of individuals varying in their strength of SI may also be affected by population density via its affect on the spatial structuring and number of S-alleles in populations. Modifiers increasing levels of self-compatibility can be selected when self-compatible individuals receive reproductive compensation by, for example, increasing seed set and/or when they become associated with high fitness genotypes. METHODS The effect of variation in the strength of SI and scrub density (low versus high) on seed set, seed germination and inbreeding depression in seed germination (delta(germ)) was investigated in the partially self-incompatible species Flourensia cernua by analysing data from self-, cross- and open-pollinated florets. KEY RESULTS Examination of 100 plants in both high and low scrub densities revealed that 51% of plants were strongly self-incompatible and 49 % varied from being self-incompatible to self-compatible. Seed set after hand cross-pollination was higher than after open-pollination for self-incompatible, partially self-incompatible and self-compatible plants but was uniformly low for strongly self-incompatible plants. Strongly self-incompatible and self-incompatible plants exhibited lower seed set, seed germination and multiplicative female fitness (floral display x seed set x seed germination) in open-pollinated florets compared with partially self-incompatible and self-compatible plants. Scrub density also had an effect on seed set and inbreeding depression: in low-density scrubs seed set was higher after open-pollination and delta(germ) was lower. CONCLUSIONS These data suggest that (a) plants suffered outcross pollen limitation, (b) female fitness in partially self-incompatible and self-compatible plants is enhanced by increased mate-compatibility and (c) plants in low-density scrubs received higher quality pollen via open-pollination than plants in high-density scrubs.
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Affiliation(s)
- Miriam M. Ferrer
- Departmento de Ecología, Universidad Autónoma de Yucatán, Km. 15·5 Carretera Mérida Xtmacuil, Mérida, Yucatán, 97000, México
| | - Sara V. Good-Avila
- Department of Biology, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB R3B2E9, Canada
| | - Carlos Montaña
- Instituto de Ecología A.C., Apartado Postal 63, Xalapa, Veracruz, CP 91070, México
| | - César A. Domínguez
- Departamento de Ecología Evolutiva, Instituto de Ecología, UNAM, Apartado Postal 70-275 México D. F., CP 04510, México
| | - Luis E. Eguiarte
- Departamento de Ecología Evolutiva, Instituto de Ecología, UNAM, Apartado Postal 70-275 México D. F., CP 04510, México
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Abstract
The occurrence of gynodioecy among angiosperms appears to be associated with self-compatibility. We use individual-based simulations to investigate the conditions for breakdown of a gametophytic self-incompatibility system in gynodioecious populations and make a comparison with hermaphroditic populations where the conditions are well known. We study three types of mutations causing self-compatibility. We track the fate of these mutations in both gynodioecious and hermaphroditic populations, where we vary the number of S-alleles, inbreeding depression and selfing rate. We find that the conditions for breakdown are less stringent if the population is gynodioecious and that the breakdown of self-incompatibility tends to promote stability of gynodioecious populations since it results in a higher frequency of females. We also find that fecundity selection has a large effect on the probability of breakdown of self-incompatibility, in particular if caused by a mutation destroying the female function of the S-locus.
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30
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Busch JW, Schoen DJ. The evolution of self-incompatibility when mates are limiting. TRENDS IN PLANT SCIENCE 2008; 13:128-36. [PMID: 18296103 DOI: 10.1016/j.tplants.2008.01.002] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2007] [Revised: 01/04/2008] [Accepted: 01/07/2008] [Indexed: 05/23/2023]
Abstract
Self-incompatibility (SI) is a genetic barrier to inbreeding that is broadly distributed in angiosperms. In finite populations of SI plants, the loss of S-allele diversity can limit plant reproduction by reducing the availability of compatible mates. Many studies have shown that small or fragmented plant populations suffer from mate limitation. The advent of molecular typing of S-alleles in many species has paved the way to address quantitatively the importance of mate limitation, and to provide greater insight into why and how SI systems breakdown frequently in nature. In this review, we highlight the ecological factors that contribute to mate limitation in SI taxa, discuss their consequences for the evolution and functioning of SI, and propose new empirical research directions.
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Affiliation(s)
- Jeremiah W Busch
- Department of Biology, McGill University, 1205 Docteur Penfield, Montreal, QC H3A 1B1, Canada.
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31
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Mena-Ali JI, Stephenson AG. Segregation analyses of partial self-incompatibility in self and cross progeny of Solanum carolinense reveal a leaky S-allele. Genetics 2007; 177:501-10. [PMID: 17660567 PMCID: PMC2013699 DOI: 10.1534/genetics.107.073775] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Natural populations of self-incompatible species often exhibit marked phenotypic variation among individuals in the strength of self-incompatibility (SI). In previous studies, we found that the strength of the SI response in Solanum carolinense, a weedy invasive with RNase-mediated SI, is a plastic trait. Selfing can be particularly important for weeds and other successional species that typically undergo repeated colonization and local extinction events and whose population sizes are often small. We applied a PCR-based protocol to identify the S-alleles present in 16 maternal genotypes and their offspring and performed a two-generation greenhouse study to determine whether variation in the strength of SI is due to the existence of weak and strong S-alleles differing in their ability to recognize and reject self-pollen. We found that allele S9 sets significantly more self seed than the other S-alleles in the population we sampled and that its ability to self is not dependent on interactions with other S-alleles. Our data suggest that the observed variations in self-fertility are likely due to factors that directly influence the expression of SI by altering the translation, turnover, or activity of the S-RNase. The variability in the strength of SI among individuals that we have observed in this and our previous studies raises the possibility that plasticity in the strength of SI in S. carolinense may play a role in the colonization and establishment of this weedy species.
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Affiliation(s)
- Jorge I Mena-Ali
- Department of Biology, Pennsylvania State University, University Park, Pennsylvania 16802, USA.
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32
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Ferrer MM, Good-Avila SV. Macrophylogenetic analyses of the gain and loss of self-incompatibility in the Asteraceae. THE NEW PHYTOLOGIST 2007; 173:401-14. [PMID: 17204086 DOI: 10.1111/j.1469-8137.2006.01905.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
The self-incompatibility (SI) status of 571 taxa from the Asteraceae was identified and the taxa were scored as having SI, partial SI or self-compatibility (SC) as their breeding system. A molecular phylogeny of the internal transcribed spacer (ITS) region was constructed for 211 of these taxa. Macrophylogenetic methods were used to test hypotheses concerning the ancestral state of SI in the Asteraceae, the gain and loss of SI, the irreversibility of the loss of SI and the potential for partial SI or SC to be terminal states. The ancestral breeding system in the family could not be resolved. Both maximum likelihood and parsimony analyses indicated that transitions among all breeding system states provide the best fit to the data and that neither partial SI nor SC is a terminal state. Furthermore, the data indicated that the loss of SI is not irreversible, although breeding system evolution has been more dynamic in some clades than in others. These results are discussed within the context of evidence for the gain and loss of SI, the evolutionary role of partial SI and methodological assumptions of tests of breeding system evolution.
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Affiliation(s)
- Miriam M Ferrer
- Department of Biology, Acadia University, Wolfville, Nova Scotia, Canada B4P 2R6
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33
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Obbard DJ, Harris SA, Buggs RJA, Pannell JR. HYBRIDIZATION, POLYPLOIDY, AND THE EVOLUTION OF SEXUAL SYSTEMS IN MERCURIALIS (EUPHORBIACEAE). Evolution 2006. [DOI: 10.1111/j.0014-3820.2006.tb00524.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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34
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Savage AE, Miller JS. Gametophytic self-incompatibility in Lycium parishii (Solanaceae): allelic diversity, genealogical structure, and patterns of molecular evolution at the S-RNase locus. Heredity (Edinb) 2006; 96:434-44. [PMID: 16622475 DOI: 10.1038/sj.hdy.6800818] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We characterized allelic diversity at the locus controlling self-incompatibility (SI) for a population of Lycium parishii (Solanaceae) from Organ Pipe National Monument, Arizona. Twenty-four partial sequences of S-RNase alleles were recovered from 25 individuals. Estimates of allelic diversity range from 23 to 27 alleles and, consistent with expectations for SI, individuals are heterozygous. We compare S-RNase diversity, patterns of molecular evolution, and the genealogical structure of alleles from L. parishii to a previously studied population of its congener L. andersonii. Gametophytic SI is well characterized for Solanaceae and although balancing selection is hypothesized to be responsible for high levels of allelic divergence, the pattern of selection varies depending on the portion of the gene considered. Site-specific models investigating patterns of selection for L. parishii and L. andersonii indicate that positive selection occurs in those regions of the S-RNase gene hypothesized as important to the recognition response, whereas positive selection was not detected for any position within regions previously characterized as conserved. A 10-species genealogy including S-RNases from a pair of congeners from each of five genera in Solanaceae reveals extensive transgeneric evolution of L. parishii S-RNases. Further, within Lycium, the Dn/Ds ratios for pairs of closely related alleles for intraspecific versus interspecific comparisons were not significantly different, suggesting that the S-RNase diversity recovered in these two species was present prior to the speciation event separating them. Despite this, two S-RNases from L. parishii are identical to two previously reported alleles for L. andersonii, suggesting gene flow between these species.
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Affiliation(s)
- A E Savage
- Department of Biology, Amherst College, McGuire Life Sciences Building, Amherst, MA 01002, USA
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35
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Thompson SL, Ritland K. A novel mating system analysis for modes of self-oriented mating applied to diploid and polyploid arctic Easter daisies (Townsendia hookeri). Heredity (Edinb) 2006; 97:119-26. [PMID: 16721390 DOI: 10.1038/sj.hdy.6800844] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
We have developed a new model for mating system analysis, which attempts to distinguish among alternative modes of self-oriented mating within populations. This model jointly estimates the rates of outcrossing, selfing, automixis and apomixis, through the use of information in the family structure given by dominant genetic marker data. The method is presented, its statistical properties evaluated, and is applied to three arctic Easter daisy populations, one consisting of diploids, the other two of tetraploids. The tetraploids are predominantly male sterile and reported to be apomictic while the diploids are male fertile. In each Easter daisy population, 10 maternal arrays of six progeny were assayed for amplified fragment length polymorphism markers. Estimates, confirmed with likelihood ratio tests of mating hypotheses, showed apomixis to be predominant in all populations (ca. 70%), but selfing or automixis was moderate (ca. 25%) in tetraploids. It was difficult to distinguish selfing from automixis, and simulations confirm that with even very large sample sizes, the estimates have a very strong negative statistical correlation, for example, they are not independent. No selfing or automixis was apparent in the diploid population, instead, moderate levels of outcrossing were detected (23%). Low but significant levels of outcrossing (2-4%) seemed to occur in the male-sterile tetraploid populations; this may be due to genotyping error of this level. Overall, this study shows apomixis can be partial, and provides evidence for higher levels of inbreeding in polyploids compared to diploids and for significant levels of apomixis in a diploid plant population.
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Affiliation(s)
- S L Thompson
- Department of Botany and Centre for Biodiversity Research, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z4.
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36
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Buggs RJA, Pannell JR. Rapid Displacement of a Monoecious Plant Lineage Is Due to Pollen Swamping by a Dioecious Relative. Curr Biol 2006; 16:996-1000. [PMID: 16713956 DOI: 10.1016/j.cub.2006.03.093] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2006] [Revised: 03/03/2006] [Accepted: 03/17/2006] [Indexed: 11/27/2022]
Abstract
Interspecific hybridization is recognized as a potentially destructive process that represents a major threat to biodiversity. The rate of population displacement by hybridization can be rapid, but underlying mechanisms are often obscure. One hypothesis is that a species may be driven to extinction by interspecific gene flow, or pollen swamping, when hybrids are inviable or sterile. Here, we document the rapid movement of two zones of contact between monoecious hexaploid and dioecious diploid populations of the wind-pollinated plant Mercurialis annua (Euphorbiaceae) in northeastern and northwestern Spain, where diploids have displaced hexaploids by about 80 and 200 km, respectively, over a period of four decades. By using experimental mating arrays, we show that hybridization is highly asymmetrical in favor of the diploids, mainly because they disperse substantially more pollen, as expected in a comparison between an obligate outcrosser and a facultative selfer. Self-fertilization, which is expected to reduce the proportion of sterile hybrids produced in mixed ploidy populations, allowed the hexaploids to avoid the effects of pollen swamping only slightly, and in a density-dependent manner. Our results thus provide a mechanistic explanation for the rapid movement of both contact zones of M. annua in Spain.
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Affiliation(s)
- Richard J A Buggs
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, United Kingdom
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37
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Stone JL, Sasuclark MA, Blomberg CP. Variation in the self-incompatibility response within and among populations of the tropical shrub Witheringia solanacea (Solanaceae). AMERICAN JOURNAL OF BOTANY 2006; 93:592-598. [PMID: 21646220 DOI: 10.3732/ajb.93.4.592] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Breakdown of genetically enforced self-incompatibility (SI), an extremely common and important evolutionary transition in plants, has conventionally been conceived as a qualitative rather than a quantitative change. We evaluated qualitative and quantitative variation in SI for four populations of Witheringia solanacea in Costa Rica, examining growth of self-pollen tubes in pollinations of buds and mature flowers. We also measured levels of RNase production in styles to determine whether enzyme production was correlated with differences in self-rejection. The two small populations contained both self-compatible (SC) individuals and obligate outcrossers (female or SI). Plants in the two large populations were uniformly SI as revealed by pollen tube growth, although several of these individuals sporadically set seed autogamously. Stylar RNase activity did not differ significantly between bud and mature flowers, but self-pollen tube growth did differ, suggesting that a gene product in addition to S-RNase is responsible for developmental onset of SI. Population-level differences in RNase activity were consistent with differences in the strength of the rejection response in bud pollinations, suggesting that a threshold level of S-RNase, in combination with other factors, is necessary for SI. Our results support a growing body of evidence that not only qualitative variation in SI, but also quantitative variation may be functionally significant.
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Affiliation(s)
- Judy L Stone
- Department of Biology, 5720 Mayflower Hill Dr., Colby College, Waterville, Maine 04901 USA
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38
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Pérez-Barrales R, Vargas P, Arroyo J. New evidence for the Darwinian hypothesis of heterostyly: breeding systems and pollinators in Narcissus sect. Apodanthi. THE NEW PHYTOLOGIST 2006; 171:553-67. [PMID: 16866958 DOI: 10.1111/j.1469-8137.2006.01819.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Here we analysed the role played by breeding systems and pollinators in the evolution of heterostyly by testing whether evolution towards heterostyly is associated with style polymorphism and changes in pollinator proficiency or breeding system variation (Darwinian hypothesis). We studied pollinators, pollen-transfer efficiency, and incompatibility systems in all seven species of Narcissus sect. Apodanthi for which we also obtained chloroplast DNA (cpDNA) sequences from three spacers to infer phylogenetic relationships. Five species are self-incompatible and within-morph cross-compatible. Heterostylous (Narcissus albimarginatus) and style-dimorphic (Narcissus cuatrecasasii) species that have a high degree of reciprocity in stigma and anther height are primarily pollinated by solitary bees. The style-monomorphic species (Narcissus watieri) and the style-dimorphic species with the least stigma-anther reciprocity (Narcissus rupicola) are both self-compatible and pollinated by butterflies, moths and hover flies. Phylogenetic reconstruction of character transitions indicates that the shift from style dimorphism to distyly is associated with a shift to bee pollination. Pollination by lepidopterans and flies is associated with stable style dimorphism and monomorphism. Evolution and maintenance of style polymorphisms in this group of species are independent of incompatibility systems. Taken together, our results strongly support the pollinator-based model for evolution of heterostyly and style length polymorphisms in general.
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Affiliation(s)
- Rocio Pérez-Barrales
- Departamento de Biología Vegetal y Ecología, Universidad de Sevilla, Apartado 1095, 41080 Seville, Spain
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Obbard DJ, Harris SA, Buggs RJA, Pannell JR. HYBRIDIZATION, POLYPLOIDY, AND THE EVOLUTION OF SEXUAL SYSTEMS IN MERCURIALIS (EUPHORBIACEAE). Evolution 2006. [DOI: 10.1554/06-104.1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Goodwillie C, Kalisz S, Eckert CG. The Evolutionary Enigma of Mixed Mating Systems in Plants: Occurrence, Theoretical Explanations, and Empirical Evidence. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2005. [DOI: 10.1146/annurev.ecolsys.36.091704.175539] [Citation(s) in RCA: 773] [Impact Index Per Article: 40.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Carol Goodwillie
- 1Department of Biology, East Carolina University, Greenville, North Carolina 27858;
| | - Susan Kalisz
- 2Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260;
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Stone JL, Pierce SE. Rapid recent radiation of S-RNase lineages in Witheringia solanacea (Solanaceae). Heredity (Edinb) 2005; 94:547-55. [PMID: 15770231 DOI: 10.1038/sj.hdy.6800657] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Strong frequency-dependent selection as found in the self-incompatibility loci of flowering plants maintains allelic lineages for extremely long time scales, such that allelic genealogies can shed insight into long-term demographic patterns of species. Effective mutation rate, as well as demographic change such as population bottlenecks, can influence genealogical structure. In addition, loss of functionality at the self-incompatibility locus is likely to affect radiation rates. Partial sequences for 21 S-RNase alleles of the mid-elevation tropical species Witheringia solanacea were obtained in order to compare their substitution rates and genealogy with those of Witheringia maculata and two species in the closely related genus Physalis. Sequences for W. solanacea fell into the three clades within the Solanaceae already identified for the genus. Terminal branch lengths for W. solanacea, scaled to the total depth of its phylogeny, were intermediate between the unusually short terminal branches of W. maculata and those of the two Physalis species. In contrast to the Physalis species, where interspecific dN/dS for closely related alleles exceeded 1.0 to the same degree as did intraspecific dN/dS, in Witheringia only intraspecific comparisons showed an excess of nonsynonymous substitutions, suggesting postspeciation radiation of alleles. Alleles associated with lowered S-RNase production and self-compatibility showed extremely short terminal branches. In summary, it appears that rapid recent diversification of alleles characterizes the Witheringia lineages. In some cases, this rapid diversification can be attributed to relaxed constraints due to breakdown of self-incompatibility.
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Affiliation(s)
- J L Stone
- Department of Biology, Colby College, Waterville, ME 04901, USA.
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Mable BK, Beland J, Di Berardo C. Inheritance and dominance of self-incompatibility alleles in polyploid Arabidopsis lyrata. Heredity (Edinb) 2005; 93:476-86. [PMID: 15266298 DOI: 10.1038/sj.hdy.6800526] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Natural populations of diploid Arabidopsis lyrata exhibit the sporophytic type of self-incompatibility system characteristic of Brassicaceae, in which complicated dominance interactions among alleles in the diploid parent determine self-recognition phenotypes of both pollen and stigma. The purpose of this study was to investigate how polyploidy affects this already complex system. One tetraploid population (Arabidopsis lyrata ssp kawasakiana from Japan) showed complete self-compatibility and produced viable selfed progeny for at least three generations subsequent to field collection. In contrast, individuals from a second tetraploid population (A. lyrata ssp petraea from Austria) were strongly self-incompatible (SI). Segregation of SI genotypes in this population followed Mendelian patterns based on a tetrasomic model of inheritance, with two to four alleles per individual, independent segregation of alleles, and little evidence of dosage effects of alleles found in multiple copies. Similar to results from diploids, anomalous compatibility patterns involving particular combinations of individuals occurred at a low frequency in the tetraploids, suggesting altered dominance in certain genetic backgrounds that could be due to the influence of a modifier locus. Overall, dominance relationships among S-alleles in self-incompatible tetraploid families were remarkably similar to those in related diploids, suggesting that this very important and complicated locus has not undergone extensive modification subsequent to polyploidization.
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Affiliation(s)
- B K Mable
- Department of Botany, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
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43
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Porcher E, Lande R. LOSS OF GAMETOPHYTIC SELF-INCOMPATIBILITY WITH EVOLUTION OF INBREEDING DEPRESSION. Evolution 2005. [DOI: 10.1554/04-171] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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PANNELL JOHNR, OBBARD DARRENJ, BUGGS RICHARDJA. Polyploidy and the sexual system: what can we learn from Mercurialis annua? Biol J Linn Soc Lond 2004. [DOI: 10.1111/j.1095-8312.2004.00340.x] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Abstract
• Researchers have hypothesized that self-compatibility (SC) should be more common in polyploid taxa than their diploid counterparts because of selection for reproductive assurance and/or the expected decline in inbreeding depression associated with having 'extra' gene copies. Support for this view has come from an observed breakdown of self-incompatibility (SI) in some species with a gametophytic system (GSI). The purpose of this research was to assess the strength of this relationship across a wider array of SI systems. • A large database, of diploid chromosome numbers, ploidy levels, and types of SI system, was assembled for angiosperm species and used to test for an association between ploidy and SC. • No strong association was found between SC and polyploidy at the level of species or families, and there was no evidence that those having a functional SI system also had fewer polyploid taxa or that most polyploids experience a breakdown in SI. • These results challenge the assumption that self-fertilization is strongly associated with polyploidy and suggest directions for further research on the evolution of polyploidy in relation to SI.
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Affiliation(s)
- Barbara K Mable
- Department of Botany, University of Guelph, Guelph, Ontario, Canada N1G 2W1
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Hancock CN, Kondo K, Beecher B, McClure B. The S-locus and unilateral incompatibility. Philos Trans R Soc Lond B Biol Sci 2003; 358:1133-40. [PMID: 12831479 PMCID: PMC1693195 DOI: 10.1098/rstb.2003.1284] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Plants have many ways to regulate the type of pollen that arrives on the stigma surface. Once there, further control mechanisms regulate compatibility. The latter controls are largely based on biochemical interactions that support compatible pollination and prevent incompatible matings. S-RNase-based self-incompatibility (SI) systems are the most phylogenetically widespread mechanisms for controlling pollination. Studies of Nicotiana establish a firm link between SI and unilateral interspecific incompatibility. Although implicated in both inter- and intraspecific compatibility, S-RNase operates through at least three distinct genetic mechanisms that differ in their dependence on non-S-RNase factors. Identification and characterization of these non-S-RNase factors is currently an area of active research. Searching for genetic and biochemical interactions with S-RNase can identify candidate non-S-RNase factors. HT-protein is one factor that is required for S-allele-specific pollen rejection in the Solanaceae. Major style arabinogalactan proteins such as TTS interact biochemically with S-RNase. These glycoproteins are known to interact with compatible pollen tubes and have long been suggested as possible recognition molecules. Their binding to S-RNase implies a link between stylar systems for compatibility and incompatibility. Thus, genetic and biochemical studies suggest a highly networked picture of pollen-pistil interactions.
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Affiliation(s)
- C Nathan Hancock
- Department of Biochemistry, University of Missouri-Columbia, 117 Schweitzer Hall, Columbia, MO 65211, USA
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O'Brien M, Kapfer C, Major G, Laurin M, Bertrand C, Kondo K, Kowyama Y, Matton DP. Molecular analysis of the stylar-expressed Solanum chacoense small asparagine-rich protein family related to the HT modifier of gametophytic self-incompatibility in Nicotiana. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2002; 32:985-96. [PMID: 12492840 DOI: 10.1046/j.1365-313x.2002.01486.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Gametophytic self-incompatibility (GSI) systems involving the expression of stylar ribonucleases have been described and extensively studied in many plant families including the Solanaceae, Rosaceae and Scrophulariaceae. Pollen recognition and rejection is governed in the style by specific ribonucleases called S-RNases, but in many self-incompatibility (SI) systems, modifier loci that can modulate the SI response have been described at the genetic level. Here, we present at the molecular level, the isolation and characterization of two Solanum chacoense homologues of the Nicotiana HT modifier that had been previously shown to be necessary for the SI reaction to occur in N. alata (McClure et al., 1999). HT homologues from other solanaceous species have also been isolated and a phylogenetic analysis reveals that the HT genes fall into two groups. In S. chacoense, these small proteins named ScHT-A and ScHT-B are expressed in the style and are developmentally regulated during anthesis identically to the S-RNases as well as following compatible and incompatible pollination. To elucidate the precise role of each HT isoform, antisense ScHT-A and RNAi ScHT-B lines were generated. Conversion from SI to self-compatibility (SC) was only observed in RNAi ScHT-B lines with reduced levels of ScHT-B mRNA. These results confirm the role of the HT modifier in solanaceous SI and indicate that only the HT-B isoform is directly involved in SI.
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Affiliation(s)
- M O'Brien
- Département de Sciences Biologiques, Institut de recherche en biologie végétale, Université de Montréal, 4101 Sherbrooke est, Montréal, Québec, Canada H1X 2B2
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Miller JS, Venable DL. The transition to gender dimorphism on an evolutionary background of self-incompatibility: an example from Lycium (Solanaceae). AMERICAN JOURNAL OF BOTANY 2002; 89:1907-1915. [PMID: 21665619 DOI: 10.3732/ajb.89.12.1907] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Populations of three North American species of Lycium (Solanaceae) are morphologically gynodioecious and consist of male-sterile (i.e., female) and hermaphroditic plants. Marked individuals were consistent in sexual expression across years and male sterility was present throughout much of the species' ranges. Controlled pollinations reveal that L. californicum, L. exsertum, and L. fremontii are functionally dioecious. Fruit production in females ranged from 36 to 63%, whereas hermaphrodites functioned essentially as males. Though hermaphrodites were mostly male, investigation of pollen tube growth reveals that hermaphrodites of all dimorphic species were self-compatible. Self-fertilization and consequent inbreeding depression are commonly invoked as important selective forces promoting the invasion of male-sterile mutants into cosexual populations. A corollary prediction of these models is that gender dimorphism evolves from self-compatible ancestors. However, fruit production, seed production, and pollen tube number following outcross pollination were significantly higher than following self-pollination for three diploid, cosexual species that are closely related to the dimorphic species. The data presented here on incompatibility systems are consistent with the hypothesis that polyploidy disrupted the self-incompatibility system in the gynodioecious species leading to the evolution of gender dimorphism.
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Affiliation(s)
- Jill S Miller
- Department of Biology, Amherst College, Amherst, Massachusetts 01002 USA
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