Genome duplication and the evolution of physiological responses to water stress

Systematic approach of polyploidy as an evolutionary genetic and genomic phenomenon in horticultural crops

Polyploidy is thought to be an evolutionary and systematic mechanism for gene flow and phenotypic advancement in flowering plants. It is a natural phenomenon that promotes diversity by creating new permutations enhancing the prime potentials as compared to progenitors. Two different pathways have been recognized in studying polyploidy in nature; mitotic or somatic chromosome doubling and cytogenetics variation. Secondly, the vital influence of being polyploid is its heritable property (unreduced reproductive cells) formed during first and second-division restitution (FDR & SDR). Different approaches either chemical (Colchicine, Oryzalin, Caffeine, Trifuralin, or phosphoric amides) or gaseous i.e. Nitrous oxide have been deliberated as strong polyploidy causing agents. A wide range of cytogenetic practices like chromosomes study, ploidy, genome analysis, and plant morphology and anatomy have been studied in different plant species. Flow cytometry for ploidy and chromosome analysis through fluorescence and genomic in situ hybridization (FISH & GISH) are the basic methods to evaluate heredity substances sampled from leaves and roots. Many horticultural crops have been developed successfully and released commercially for consumption. Moreover, some deep detailed studies are needed to check the strong relationship between unique morphological features and genetic makeup concerning genes and hormonal expression in a strong approach.

Ice age-driven range shifts of diploids and expanding autotetraploids of Biscutella laevigata within a conserved niche

Early studies of the textbook mixed-ploidy system Biscutella laevigata highlighted diploids restricted to never-glaciated lowlands and tetraploids at high elevations across the European Alps, promoting the hypothesis that whole-genome duplication (WGD) is advantageous under environmental changes. Here we addressed long-held hypotheses on the role of hybridisation at the origin of the tetraploids, their single vs multiple origins, and whether a shift in climatic niche accompanied WGD. Climatic niche modelling together with spatial genetics and coalescent modelling based on ddRAD-seq genotyping of 17 diploid and 19 tetraploid populations was used to revisit the evolution of this species complex in space and time. Diploids differentiated into four genetic lineages corresponding to allopatric glacial refugia at the onset of the last ice age, whereas tetraploids displaying tetrasomic inheritance formed a uniform group that originated from southern diploids before the last glacial maximum. Derived from diploids occurring at high elevation, autotetraploids likely inherited their adaptation to high elevation rather than having evolved it through or after WGD. They further presented considerable postglacial expansion across the Alps and underwent admixture with diploids. Although the underpinnings of the successful expansion of autotetraploids remain elusive, differentiation in B. laevigata was chiefly driven by the glacial history of the Alps.

Genome-Wide Identification and Evolution-Profiling Analysis of TPS Gene Family in Triticum Plants

Terpenoids play a crucial role in plant growth and development, as well as in regulating resistance mechanisms. Terpene synthase (TPS) serves as the final step in the synthesis process of terpenoids. However, a comprehensive bioinformatics analysis of the TPS gene family in Triticum plants had not previously been systematically undertaken. In this study, a total of 531 TPS members were identified in Triticum plants. The evolutionary tree divided the TPS proteins into five subfamilies: Group1, Group2, Group3, Group4, and Group5. The results of the duplication events analysis showed that TD and WGD were major driving forces during the evolution of the TPS family. The cis-element analysis showed that the TPS genes were related to plant growth and development and environmental stress. Moreover, the GO annotation displayed that the biological function of TPS was relatively conserved in wheat plants. The RNA-seq data showed that the rice and wheat TPS genes responded to low-temperature stress and exhibited significantly different expression patterns. This research shed light on the functions of TPSs in responding to abiotic stress and demonstrated their modulatory potential during root development. These findings provide a foundation for further and deeper investigation of the TPSs' functions in Triticum plants.

Polyploidy and environmental stress response: a comparative study of fern gametophytes

Climate change is rapidly altering natural habitats and generating complex patterns of environmental stress. Ferns are major components of many forest understories and, given their independent gametophyte generation, may experience unique pressures in emerging temperature and drought regimes. Polyploidy is widespread in ferns and may provide a selective advantage in these rapidly changing environments. This work aimed to understand whether the gametophytes of allopolyploid ferns respond differently to climate-related physiological stress than their diploid parents. The experimental approach involved a multifactorial design with 27 treatment combinations including exposure to multiple levels of drought and temperature over three treatment durations, with recovery measured at multiple timepoints. We measured Chl fluorescence from over 2000 gametophytes to evaluate stress avoidance and tolerance in diploid and polyploid species. Polyploids generally showed a greater ability to avoid and/or tolerate a range of stress conditions compared with their diploid counterparts, suggesting that polyploidy may confer enhanced flexibility and resilience under climate stress. Overall, these results suggest that polyploidy may provide some resilience to climate change in mixed ploidy populations. However, all species remain susceptible to the impacts of extreme drought and heat stress.

Cryptic diploid lineage of Betula ermanii at its southern boundary populations in Japan

Polyploidy is thought to enable species diversification and adaptation to extreme environments. Resolving the ecological differences between a taxon's ploidy levels would therefore provide important insights into local adaptation and speciation. The genus Betula includes many polyploids, but estimates of their phylogenetic relationships and evolutionary history are uncertain because of cryptic lineages and species. As one of the southern boundary populations of Betula ermanii in Japan has been shown to have distinctive genetic characteristics and traits, the differences in ploidy levels between three southern boundary and various other Japanese B. ermanii populations were investigated using flow cytometry. Leaf and seed morphologies were also compared. Apart from individuals in southern boundary populations, all those sampled were tetraploid. Individuals from the southern boundary populations were mostly diploid, apart from a few from lower altitude Shikoku populations, which were tetraploid. Leaf and seed morphologies differed between tetraploids and diploids. Diploid individuals were characterized by leaves with a heart-shaped base and many leaf teeth, and seeds with relatively longer wings. The diploid populations could be considered a cryptic relict lineage of B. ermanii, and there is a possibility that this lineage is a diploid ancestor of B. ermanii and a relict population of the Sohayaki element. Further investigation of the Japanese Betula phylogenetic relationships would enable an informed discussion of taxonomic revisions.

Clonal growth characteristics and diversity patterns of different Clintonia udensis (Liliaceae) diploid and tetraploid cytotypes in the Hualongshan Mountains

Polyploidization plays an important role in plant evolution and biodiversity. However, intraspecific polyploidy compared to interspecific polyploidy received less attention. Clintonia udensis (Liliaceae) possess diploid (2n = 2x = 14) and autotetraploid (2n = 4x = 28) cytotypes. In the Hualongshan Mountains, the autotetraploids grew on the northern slope, while the diploids grew on the southern slopes. The clonal growth characteristics and clonal architecture were measured and analyzed by field observations and morphological methods. The diversity level and differentiation patterns for two different cytotypes were investigated using SSR markers. The results showed that the clonal growth parameters, such as the bud numbers of each rhizome node and the ratio of rhizome branches in the autotetraploids were higher than those in the diploids. Both the diploids and autotetraploids appeared phalanx clonal architectures with short internodes between ramets. However, the ramets or genets of the diploids had a relatively scattered distribution, while those of the autotetraploids were relatively clumping. The diploids and autotetraploids all allocated more biomass to their vegetative growth. The diploids had a higher allocation to reproductive organs than that of autotetraploids, which indicated that the tetraploids invested more resources in clonal reproduction than diploids. The clone diversity and genetic diversity of the autotetraploids were higher than that of the diploids. Significant genetic differentiation between two different cytotypes was observed (P < 0.01). During establishment and evolution, C. udensis autotetraploids employed more clumping phalanx clonal architecture and exhibited more genetic variation than the diploids.

A unified framework to investigate and interpret hybrid and allopolyploid biodiversity across biological scales

Premise

Hybridization and polyploidization are common in vascular plants and important drivers of biodiversity by facilitating speciation and ecological diversification. A primary limitation to making broad synthetic discoveries in hybrid and allopolyploid biodiversity research is the absence of a standardized framework to compare data across studies and biological scales.

Methods

Here, I present a new quantitative framework to investigate and interpret patterns in hybrid and allopolyploid biology called the divergence index (DI). The DI framework produces standardized data that are comparable across studies and variables. To show how the DI framework can be used to synthesize data, I analyzed published biochemical, physiological, and ecological trait data of hybrids and allopolyploids. I also apply key ecological and evolutionary concepts in hybrid and polyploid biology to translate nominal outcomes, including transgression, intermediacy, expansion, and contraction, in continuous DI space.

Results

Biochemical, physiological, ecological, and evolutionary data can all be analyzed, visualized, and interpreted in the DI framework. The DI framework is particularly suited to standardize and compare variables with very different scales. When using the DI framework to understand niche divergence, a metric of niche overlap can be used to complement insights to centroid and breadth changes.

Discussion

The DI framework is an accessible framework for hybrid and allopolyploid biology and represents a flexible and intuitive tool that can be used to reconcile outstanding problems in plant biodiversity research.

Recent advancements in the physiological, genetic, and genomic research on Rhododendrons for trait improvement

High species diversity, hybridization potential, broad geographical dispersal range and ornamental characteristics (i.e., attractive size, shape, structure, flowers, and evergreen) have fetched a good international market for Rhododendron. However, most species are restricted to specific geographic areas due to their habitat specificity in acidic soil and cold climates, resulting many species being classified under threat categories of the IUCN. In this review, advances in research on Rhododendron for improvement to floral display quality and stress resistance have been described. The low genetic barrier among species has created opportunities for extensive hybridization and ploidy alteration for introducing quality and adaptive traits during the development of new varieties. Recent technological advances have supported investigations into the mechanism of flower development, as well as cold tolerance and pathogen resistance mechanisms in the Rhododendron. However, most of the species have limited adaptability to drought, line-tolerance, pathogen resistance, and high-temperature conditions and this resistance ability present in few species largely remains unexplored. Additionally, the available genetic diversity and genomic information on species, and possibilities for their application in molecular breeding have been summarized. Overall, genomic resource data are scarce in the majority of the members of this genus. Finally, various research gaps such as genetic mapping of quality traits, understanding the molecular mechanism of quality-related traits and genomic assortment in Rhododendron members have been discussed in the future perspective section.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04006-6.

Accession-specific parent-of-origin dependent and independent genome dosage effects on salt tolerance in Arabidopsis thaliana

Improving the salt stress tolerance of crops is an important goal in plant breeding. Changes in the number of chromosome sets (i.e. ploidy level) cause genome dosage effects which can result in enhanced or novel traits. Maternal inheritance versus paternal inheritance of the same chromosome sets can have differential epigenetic effects on traits of F1 offspring. Hence, genome dosage effects can be parent-of-origin independent or dependent. The model plant Arabidopsis thaliana displays both genome dosage and parent-of-origin effects on plant growth under non-stress conditions. Using an isogenic ploidy series of diploid, triploid and tetraploid lines, we investigate the extent of genome dosage effects and their parent-of-origin dependency on in vitro salt stress tolerance of seedlings across 10 different A. thaliana accessions (genetic backgrounds). We detected genome dosage effects on salt stress tolerance for tetraploid lines in five accessions. In addition, through the generation of isogenic reciprocal F1 triploid lines, both parent-of-origin dependent and independent genome dosage effects on salt stress tolerance were detected. Thus, our results indicate not only that genome dosage balance effects can have significant impacts on abiotic stress tolerance in A. thaliana but also that parent-of-origin specific genome dosage effects can affect salt stress tolerance in plants.

Ploidy's Role in Daylily Plant Resilience to Drought Stress Challenges

This study aimed to understand the differences in the performance of diploid and tetraploid daylily cultivars under water deficit conditions, which are essential indicators of drought tolerance. This research revealed that tetraploid daylilies performed better than diploid varieties in arid conditions due to their enhanced adaptability and resilience to water deficit conditions. The analysis of the results highlighted the need to clarify the specific physiological and molecular mechanisms underlying the enhanced drought tolerance observed in tetraploid plants compared to diploids. This research offers valuable knowledge for improving crop resilience and sustainable floricultural practices in changing environmental conditions. The morphological and physiological parameters were analyzed in 19 diploid and 21 tetraploid daylily cultivars under controlled water deficit conditions, and three drought resistance groups were formed based on the clustering of these parameters. In a high drought resistance cluster, 93.3% tetraploid cultivars were exhibited. This study demonstrates the significance of ploidy in shaping plant responses to drought stress. It emphasizes the importance of studying plant responses to water deficit in landscape horticulture to develop drought-tolerant plants and ensure aspects of climate change.

Traits-based approach: leveraging genome size in plant-microbe interactions

Trait-based approaches have gained growing interest in studying plant-microbe interactions. However, current traits normally considered (e.g., morphological, physiological, or chemical traits) are biased towards those showing large intraspecific variations, necessitating the identification of fewer plastic traits that differ between species. Here, we propose using genome size (the amount of DNA in the nucleus of a cell) as a suitable trait for studying plant-microbiome interactions due to its relatively stable nature, minimally affected by external environmental variations. Emerging evidence suggests that plant genome size affects the plant-associated microbial community, and tissue-specific environments select microbes based on their genome size. These findings pinpoint environmental selection in genome size as an emerging driver of plant-microbiome interactions, potentially impacting ecosystem functions and productivity.

Polyploid tubular cells: a shortcut to stress adaptation

Tubular epithelial cells (TCs) compose the majority of kidney parenchyma and play fundamental roles in maintaining homeostasis. Like other tissues, mostly immature TC with progenitor capabilities are able to replace TC lost during injury via clonal expansion and differentiation. In contrast, differentiated TC lack this capacity. However, as the kidney is frequently exposed to toxic injuries, evolution positively selected a response program that endows differentiated TC to maintain residual kidney function during kidney injury. Recently, we and others have described polyploidization of differentiated TC, a mechanism to augment the function of remnant TC after injury by rapid hypertrophy. Polyploidy is a condition characterized by >2 complete sets of chromosomes. Polyploid cells often display an increased functional capacity and are generally more resilient to stress as evidenced by being conserved across many plants and eukaryote species from flies to mammals. Here, we discuss the occurrence of TC polyploidy in different contexts and conditions and how this integrates into existing concepts of kidney cell responses to injury. Collectively, we aim at stimulating the acquisition of novel knowledge in the kidney field as well as accelerating the translation of this basic response mechanism to the clinical sphere.

Integrating genes and metabolites: unraveling mango's drought resilience mechanisms

BACKGROUND

Mango (Mangifera indica L.) faces escalating challenges from increasing drought stress due to erratic climate patterns, threatening yields, and quality. Understanding mango's drought response mechanisms is pivotal for resilience and food security.

RESULTS

Our RNA-seq analyses unveil 12,752 differentially expressed genes linked to stress signaling, hormone regulation, and osmotic adjustment. Weighted Gene Co-expression Network Analysis identified three essential genes-WRKY transcription factor 3, polyamine oxidase 4, and protein MEI2-like 1-as drought defense components. WRKY3 having a role in stress signaling and defense validates its importance. Polyamine oxidase 4, vital in stress adaptation, enhances drought defense. Protein MEI2-like 1's significance emerges, hinting at novel roles in stress responses. Metabolite profiling illuminated Mango's metabolic responses to drought stress by presenting 990 differentially abundant metabolites, mainly related to amino acids, phenolic acids, and flavonoids, contributing to a deeper understanding of adaptation strategies. The integration between genes and metabolites provided valuable insights by revealing the correlation of WRKY3, polyamine oxidase 4 and MEI2-like 1 with amino acids, D-sphingnosine and 2,5-Dimethyl pyrazine.

CONCLUSIONS

This study provides insights into mango's adaptive tactics, guiding future research for fortified crop resilience and sustainable agriculture. Harnessing key genes and metabolites holds promise for innovative strategies enhancing drought tolerance in mango cultivation, contributing to global food security efforts.

Physiology, gene expression, and epiphenotype of two Dianthus broteri polyploid cytotypes under temperature stress

Increasing evidence supports a major role for abiotic stress response in the success of plant polyploids, which usually thrive in harsh environments. However, understanding the ecophysiology of polyploids is challenging due to interactions between genome doubling and natural selection. Here, we investigated physiological responses, gene expression, and the epiphenotype of two related Dianthus broteri cytotypes-with different genome duplications (4× and 12×) and evolutionary trajectories-to short extreme temperature events (42/28 °C and 9/5 °C). The 12× cytotype showed higher expression of stress-responsive genes (SWEET1, PP2C16, AI5L3, and ATHB7) and enhanced gas exchange compared with 4×. Under heat stress, both ploidies had greatly impaired physiological performance and altered gene expression, with reduced cytosine methylation. However, the 12× cytotype exhibited remarkable physiological tolerance (maintaining gas exchange and water status via greater photochemical integrity and probably enhanced water storage) while down-regulating PP2C16 expression. Conversely, 4× D. broteri was susceptible to thermal stress despite prioritizing water conservation, showing signs of non-stomatal photosynthetic limitations and irreversible photochemical damage. This cytotype also presented gene-specific expression patterns under heat, up-regulating ATHB7. These findings provide insights into divergent stress response strategies and physiological resistance resulting from polyploidy, highlighting its widespread influence on plant function.

Separating phases of allopolyploid evolution with resynthesized and natural Capsella bursa-pastoris

Allopolyploidization is a frequent evolutionary transition in plants that combines whole-genome duplication (WGD) and interspecific hybridization. The genome of an allopolyploid species results from initial interactions between parental genomes and long-term evolution. Distinguishing the contributions of these two phases is essential to understanding the evolutionary trajectory of allopolyploid species. Here, we compared phenotypic and transcriptomic changes in natural and resynthesized Capsella allotetraploids with their diploid parental species. We focused on phenotypic traits associated with the selfing syndrome and on transcription-level phenomena such as expression-level dominance (ELD), transgressive expression (TRE), and homoeolog expression bias (HEB). We found that selfing syndrome, high pollen, and seed quality in natural allotetraploids likely resulted from long-term evolution. Similarly, TRE and most down-regulated ELD were only found in natural allopolyploids. Natural allotetraploids also had more ELD toward the self-fertilizing parental species than resynthesized allotetraploids, mirroring the establishment of the selfing syndrome. However, short-term changes mattered, and 40% of the cases of ELD in natural allotetraploids were already observed in resynthesized allotetraploids. Resynthesized allotetraploids showed striking variation of HEB among chromosomes and individuals. Homoeologous synapsis was its primary source and may still be a source of genetic variation in natural allotetraploids. In conclusion, both short- and long-term mechanisms contributed to transcriptomic and phenotypic changes in natural allotetraploids. However, the initial gene expression changes were largely reshaped during long-term evolution leading to further morphological changes.

Foliar Pectins and Physiology of Diploid and Autotetraploid Mango Genotypes under Water Stress

The cultivation of mango in Mediterranean-type climates is challenged by the depletion of freshwater. Polyploids are alternative genotypes with potential greater water use efficiency, but field evaluations of the anatomy and physiology of conspecific adult polyploid trees under water stress remain poorly explored. We combined field anatomical evaluations with measurements of leaf water potential (Ψl) and stomatal conductance (Gs) comparing one diploid and one autotetraploid tree per treatment with and without irrigation during dry summers (when fruits develop). Autotetraploid leaves displayed lower Ψl and Gs in both treatments, but the lack of irrigation only affected Gs. Foliar cells of the adaxial epidermis and the spongy mesophyll contained linear pectin epitopes, whereas branched pectins were localized in the abaxial epidermis, the chloroplast membrane, and the sieve tube elements of the phloem. Cell and fruit organ size was larger in autotetraploid than in diploid mango trees, but the sugar content in the fruits was similar between both cytotypes. Specific cell wall hygroscopic pectins correlate with more stable Ψl of autotetraploid leaves under soil water shortage, keeping lower Gs compared with diploids. These preliminary results point to diploids as more susceptible to water deficits than tetraploids.

Biogeography and the evolution of acoustic communication in the polyploid North American grey treefrog complex

After polyploid species are formed, interactions between diploid and polyploid lineages may generate additional diversity in novel cytotypes and phenotypes. In anurans, mate choice by acoustic communication is the primary method by which individuals identify their own species and assess suitable mates. As such, the evolution of acoustic signals is an important mechanism for contributing to reproductive isolation and diversification in this group. Here, we estimate the biogeographical history of the North American grey treefrog complex, consisting of the diploid Hyla chrysoscelis and the tetraploid Hyla versicolor, focusing specifically on the geographical origin of whole genome duplication and the expansion of lineages out of glacial refugia. We then test for lineage-specific differences in mating signals by applying comparative methods to a large acoustic data set collected over 52 years that includes >1500 individual frogs. Along with describing the overall biogeographical history and call diversity, we found evidence that the geographical origin of H. versicolor and the formation of the midwestern polyploid lineage are both associated with glacial limits, and that the southwestern polyploid lineage is associated with a shift in acoustic phenotype relative to the diploid lineage with which they share a mitochondrial lineage. In H. chrysoscelis, we see that acoustic signals are largely split by Eastern and Western lineages, but that northward expansion along either side of the Appalachian Mountains is associated with further acoustic diversification. Overall, results of this study provide substantial clarity on the evolution of grey treefrogs as it relates to their biogeography and acoustic communication.

Effects of Allopolyploidization and Homoeologous Chromosomal Segment Exchange on Homoeolog Expression in a Synthetic Allotetraploid Wheat under Variable Environmental Conditions

Allopolyploidy through the combination of divergent genomes into a common nucleus at doubled dosage is known as a potent genetic and evolutionary force. As a macromutation, a striking feature of allopolyploidy in comparison with other mutational processes is that 'genome shock' can be evoked, thereby generating rapid and saltational biological consequences. A major manifestation of genome shock is genome-wide gene expression rewiring, which previously remained to be fully elucidated. Here, using a large set of RNAseq-based transcriptomic data of a synthetic allotetraploid wheat (genome AADD) and its parental species, we performed in-depth analyses of changes in the genome-wide gene expression under diverse environmental conditions at the subgenome (homoeolog) level and investigated the additional effects of homoeologous chromosomal segment exchanges (abbreviated HEs). We show that allopolyploidy caused large-scale changes in gene expression that were variable across the conditions and exacerbated by both stresses and HEs. Moreover, although both subgenomes (A and D) showed clear commonality in the changes, they responded differentially under variable conditions. The subgenome- and condition-dependent differentially expressed genes were enriched for different gene ontology terms implicating different biological functions. Our results provide new insights into the direct impacts of allopolyploidy on condition-dependent changes in subgenome expression and the additional effects of HEs in nascent allopolyploidy.

2-Oxoglutarate contributes to the effect of foliar nitrogen on enhancing drought tolerance during flowering and grain yield of soybean

Drought severely affects the growth and yield of soybean plants especially during the flowering period. To investigate the effect of 2-oxoglutarate (2OG) in combination with foliar nitrogen (N) at flowering stage on drought resistance and seed yield of soybean under drought stress. This experiment was conducted in 2021 and 2022 on drought-resistant variety (Hefeng 50) and drought-sensitive variety (Hefeng 43) soybean plants treated with foliar N (DS + N) and 2-oxoglutarate (DS + 2OG) at flowering stage under drought stress. The results showed that drought stress at flowering stage significantly increased leaf malonaldehyde (MDA) content and reduced soybean yield per plant. However, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities were significantly increased by foliar N treatment, and 2-oxoglutarate synergistically with foliar N treatment (DS + N + 2OG) was more beneficial to plant photosynthesis. 2-oxoglutarate significantly enhanced plant N content, glutamine synthetase (GS) and glutamate synthase (GOGAT) activity. Furthermore, 2-oxoglutarate increased the accumulation of proline and soluble sugars under drought stress. Under drought stress, soybean seed yield was increased by DS + N + 2OG treatment by 16.48-17.10% and 14.96-18.84% in 2021 and 2022, respectively. Thus, the combination of foliar N and 2-oxoglutarate better mitigated the adverse effects of drought stress and could better compensate for the yield loss of soybean under drought stress.

Hydraulic trade-offs underlie enhanced performance of polyploid trees under soil water deficit

The relationships between aerial organ morpho-anatomy of woody polyploid plants with their functional hydraulics under water stress remain largely understudied. We evaluated growth-associated traits, aerial organ xylem anatomy, and physiological parameters of diploid, triploid, and tetraploid genotypes of atemoyas (Annona cherimola x Annona squamosa), which belong to the woody perennial genus Annona (Annonaceae), testing their performance under long-term soil water reduction. The contrasting phenotypes of vigorous triploids and dwarf tetraploids consistently showed stomatal size-density trade-off. The vessel elements in aerial organs were ∼1.5 times wider in polyploids compared with diploids, and triploids displayed the lowest vessel density. Plant hydraulic conductance was higher in well-irrigated diploids while their tolerance to drought was lower. The phenotypic disparity of atemoya polyploids associated with contrasting leaf and stem xylem porosity traits that coordinate to regulate water balances between the trees and the belowground and aboveground environments. Polyploid trees displayed better performance under soil water scarcity, presenting as more sustainable agricultural and forestry genotypes to cope with water stress.

Learning to tango with four (or more): the molecular basis of adaptation to polyploid meiosis

Polyploidy, which arises from genome duplication, has occurred throughout the history of eukaryotes, though it is especially common in plants. The resulting increased size, heterozygosity, and complexity of the genome can be an evolutionary opportunity, facilitating diversification, adaptation and the evolution of functional novelty. On the other hand, when they first arise, polyploids face a number of challenges, one of the biggest being the meiotic pairing, recombination and segregation of the suddenly more than two copies of each chromosome, which can limit their fertility. Both for developing polyploidy as a crop improvement tool (which holds great promise due to the high and lasting multi-stress resilience of polyploids), as well as for our basic understanding of meiosis and plant evolution, we need to know both the specific nature of the challenges polyploids face, as well as how they can be overcome in evolution. In recent years there has been a dramatic uptick in our understanding of the molecular basis of polyploid adaptations to meiotic challenges, and that is the focus of this review.

Impact of genome duplications in drought tolerance and distribution of the diploid-tetraploid Jasione maritima

Polyploidy has important ecological effects, including ploidy-mediated effects on morphology, breeding system and ecological tolerances. However, there is still little comprehensive research available to test its adaptive significance and its role in driving distributional patterns. This work aimed to assess the contribution of genome duplications to ecological divergence using an experimental approach with the diploid-tetraploid Jasione maritima polyploid complex. We explored if individuals with different ploidy differ in their tolerance to water deficit and if this may contribute to explaining the distribution patterns along a latitudinal gradient in the northwest Iberian Peninsula. For that, we used three cytogenetic entities: diploids and established tetraploids collected in natural populations along a latitudinal gradient, and neotetraploids synthesized from diploid populations after treatments with colchicine. Thirty plants from each of the nine populations were grown under controlled conditions with half randomly assigned to the water deficit treatment, and half used as control. We determined experimental plants' response by measuring fitness-related parameters, such as above and belowground biomass, plant water status, photosynthetic efficiency and pigments, membrane stability, antioxidant capacity and sugars content. Our data shows that biomass, chlorophyll content, photochemical quenching (qP) and non-photochemical quenching (NPQ) in neotetraploids and established tetraploids were significantly higher than in diploids and that these differences could be attributed to genome duplications. In response to the water deficit, diploids seem to use a strategy of avoidance, whereas tetraploids seem to employ the strategy of tolerance to overcome water deficit stress, which appears equally efficient. Additionally, we did not observe a response pattern along the latitudinal gradient of the distributional range of the J. maritima complex. The results indicate that the response to water deficit is population dependent. Further studies are necessary to understand the role of ploidy in explaining the distribution patterns of the J. maritima complex.

The immediate effects of polyploidization of Spirodela polyrhiza change in a strain-specific way along environmental gradients

The immediate effects of plant polyploidization are well characterized and it is generally accepted that these morphological, physiological, developmental, and phenological changes contribute to polyploid establishment. Studies on the environmental dependence of the immediate effects of whole-genome duplication (WGD) are, however, scarce but suggest that these immediate effects are altered by stressful conditions. As polyploid establishment seems to be associated with environmental disturbance, the relationship between ploidy-induced phenotypical changes and environmental conditions is highly relevant. Here, we use a common garden experiment on the greater duckweed Spirodela polyrhiza to test whether the immediate effects of WGD can facilitate the establishment of tetraploid duckweed along gradients of two environmental stressors. Because successful polyploid establishment often depends on recurrent polyploidization events, we include four genetically diverse strains and assess whether these immediate effects are strain-specific. We find evidence that WGD can indeed confer a fitness advantage under stressful conditions and that the environment affects ploidy-induced changes in fitness and trait reaction norms in a strain-specific way.

How plants conquered land: evolution of terrestrial adaptation

The transition of plants from water to land is considered one of the most significant events in the evolution of life on Earth. The colonization of land by plants, accompanied by their morphological, physiological and developmental changes, resulted in plant biodiversity. Besides significantly influencing oxygen levels in the air and on land, plants manufacture organic matter from CO₂ and water with the help of sunlight, paving the way for the diversification of nonplant lineages ranging from microscopic organisms to animals. Land plants regulate the climate by adjusting total biomass and energy flow. At the genetic level, these innovations are achieved through the rearrangement of pre-existing genetic information. Advances in genome sequencing technology are revamping our understanding of plant evolution. This study highlights the morphological and genomic innovations that allow plants to integrate life on Earth.

Ecological niches in the polyploid complex Linum suffruticosum s.l

Introduction

The high frequency of polyploidy in the evolutionary history of many plant groups occurring in the Mediterranean region is likely a consequence of its dynamic paleogeographic and climatic history. Polyploids frequently have distinct characteristics that allow them to overcome the minority cytotype exclusion. Such traits may enable polyploid individuals to grow in habitats different from their parentals and/or expand to new areas, leading to spatial segregation. Therefore, the successful establishment of polyploid lineages has long been associated with niche divergence or niche partitioning and the ability of polyploids to cope with different, often more stressful, conditions. In this study, we aimed to explore the role of environmental variables associated with the current distribution patterns of cytotypes within the polyploid complex Linum suffruticosum s.l..

Methods

The distribution and environmental niches of the five main cytotypes of Linum suffruticosum s.l. (diploids, tetraploids, hexaploids, octoploids and decaploids) were studied across its distribution range. Realized environmental niche of each cytotype was determined using niche modelling tools, such as maximum entropy modelling and niche equivalency and similarity tests.

Results

Differences in the environmental conditions of L. suffruticosum s.l. cytotypes were observed, with polyploids being associated with habitats of increased drought and soil pH, narrower temperature ranges and decreased soil water and cation exchange capacities. Diploids present the widest environmental niche, and polyploids occupy part of the diploid niche. Although some polyploids have equivalent potential ecological niches, cytotypes do not co-occur in nature. Additionally, the ecological niche of this polyploid complex is different between continents, with North African habitats being characterised by differences in soil texture, higher pH, and low cation exchange capacity, precipitation and soil water capacity and higher temperatures than habitats in southwest Europe.

Discussion

The different ecological conditions played a role in the distribution of cytotypes, but the mosaic distribution could not be entirely explained by the environmental variables included in this study. Other factors, such as reproductive isolation and competitive interactions among cytotypes, could further explain the current diversity and distribution patterns in white flax. This study provides relevant data on the niche requirements of each cytotype for further competition and reciprocal transplant experiments. further competition and reciprocal transplant experiments.

Homoeologous exchange enables rapid evolution of tolerance to salinity and hyper-osmotic stresses in a synthetic allotetraploid wheat

The link between polyploidy and enhanced adaptation to environmental stresses could be a result of polyploidy itself harbouring higher tolerance to adverse conditions, or polyploidy possessing higher evolvability than diploids under stress conditions. Natural polyploids are inherently unsuitable to disentangle these two possibilities. Using selfed progenies of a synthetic allotetraploid wheat AT3 (AADD) along with its diploid parents, Triticum urartu TMU38 (AA) and Aegilops tauschii TQ27 (DD), we addressed the foregoing issue under abiotic salinity and hyper-osmotic (drought-like) stress. Under short duration of both stresses, euploid plants of AT3 showed intermediate tolerance of diploid parents; under life-long duration of both stresses, tolerant individuals to either stress emerged from selfed progenies of AT3, but not from comparable-sized diploid parent populations. Tolerance to both stresses were conditioned by the same two homoeologous exchanges (HEs; 2DS/2AS and 3DL/3AL), and at least one HE needed to be at the homozygous state. Transcriptomic analyses revealed that hyper-up-regulation of within-HE stress responsive genes of the A sub-genome origin is likely responsible for the dual-stress tolerant phenotypes. Our results suggest that HE-mediated inter-sub-genome rearrangements can be an important mechanism leading to adaptive evolution in allopolyploids as well as a promising target for genetic manipulation in crop improvement.

Autotetraploidization Gives Rise to Differential Gene Expression in Response to Saline Stress in Rice

Plant polyploidization represents an effective means for plants to perpetuate their adaptive advantage in the face of environmental variation. Numerous studies have identified differential responsiveness to environmental cues between polyploids and their related diploids, and polyploids might better adapt to changing environments. However, the mechanism that underlies polyploidization contribution during abiotic stress remains hitherto obscure and needs more comprehensive assessment. In this study, we profile morphological and physiological characteristics, and genome-wide gene expression between an autotetraploid rice and its diploid donor plant following saline stress. The results show that the autotetraploid rice is more tolerant to saline stress than its diploid precursor. The physiological characteristics were rapidly responsive to saline stress in the first 24 h, during which the elevations in sodium ion, superoxide dismutase, peroxidase, and 1-aminocyclopropane-1-carboxylic acid were all significantly higher in the autotetraploid than in the diploid rice. Meanwhile, the genome-wide gene expression analysis revealed that the genes related to ionic transport, peroxidase activity, and phytohormone metabolism were differentially expressed in a significant manner between the autotetraploid and the diploid rice in response to saline stress. These findings support the hypothesis that diverse mechanisms exist between the autotetraploid rice and its diploid donor plant in response to saline stress, providing vital information for improving our understanding on the enhanced performance of polyploid plants in response to salt stress.

Do water and soil nutrient scarcities differentially impact the performance of diploid and tetraploid Solidago gigantea (Giant Goldenrod, Asteraceae)?

Plants require water and nutrients for survival, although the effects of their availabilities on plant fitness differ amongst species. Genome size variation, within and across species, is suspected to influence plant water and nutrient requirements, but little is known about how variations in these resources concurrently affect plant fitness based on genome size. We examined how genome size variation between autopolyploid cytotypes influences plant morphological and physiological traits, and whether cytotype-specific trait responses differ based on water and/or nutrient availability. Diploid and autotetraploid Solidago gigantea (Giant Goldenrod) were grown in a greenhouse under four soil water:N+P treatments (L:L, L:H, H:L, H:H), and stomata characteristics (size, density), growth (above- and belowground biomass, R/S), and physiological (A_net , E, WUE) responses were measured. Resource availabilities and cytotype identity influenced some plant responses but their effects were independent of each other. Plants grown in high-water and nutrient treatments were larger, plants grown in low-water or high-nutrient treatments had higher WUE but lower E, and A_net and E rates decreased as plants aged. Autotetraploids also had larger and fewer stomata, higher biomass and larger A_net than diploids. Nutrient and water availability could influence intra- and interspecific competitive outcomes. Although S. gigantea cytotypes were not differentially affected by resource treatments, genome size may influence cytogeographic range patterning and population establishment likelihood. For instance, the larger size of autotetraploid S. gigantea might render them more competitive for resources and niche space than diploids.

Autopolyploid establishment depends on life-history strategy and the mating outcomes of clonal architecture

Polyploidy is a significant component in the evolution of many taxa, particularly plant groups. However, new polyploids face substantial fitness disadvantages due to a lack of same-cytotype mates, and the factors promoting or preventing polyploid establishment in natural populations are often unclear. We develop spatially explicit agent-based simulation models to test the hypothesis that a perennial life history and clonal propagation facilitate the early stages of polyploid establishment and persistence. Our models show that polyploids are more likely to establish when they have longer life spans than diploids, especially when self-fertilization rates are high. Polyploids that combine sexual and clonal reproduction can establish across a wide range of life histories, but their success is moderated by clonal strategy. By tracking individuals and mating events, we reveal that clonal architecture has a substantial impact on the spatial structure of the mixed diploid-polyploid population during polyploid establishment: altering patterns of mating within or between cytotypes via geitonogamous self-fertilization, the mechanisms through which polyploid establishment proceeds, and the final composition of the polyploid population. Overall, our findings provide novel insight into the role of clonal structure in modulating the complex relationship between polyploidy, perenniality, and clonality and offer testable predictions for future empirical work.

Polyploidy increases storage but decreases structural stability in Arabidopsis thaliana

Whole-genome duplication, leading to polyploidy and endopolyploidy, is widespread throughout the tree of life.^1-3 Both polyploidy and endopolyploidy can increase cell size via nucleotypic effects, but the phenotypic consequences of increased cell size at the tissue and whole-organism levels are less well understood.^1-4 We quantified the consequences of autopolyploidy and endopolyploidy in nine diploid accessions of Arabidopsis thaliana, representing a gradient in endopolyploidy, to their corresponding experimentally synthesized neo-tetraploid and neo-octoploid cytotypes. The increase in cell size following genome duplication increased plant storage capacity, which increased tolerance of resource limitation, but also incurred biomechanical costs because of a reduction in the amount of cell wall per unit tissue volume. Our findings also show that the functional consequences of autopolyploidy can vary with accession identity, and the presence of this variation suggests that there is potential for adaptation following whole-genome duplication.

Polyploidy in urban environments

Polyploidy is a major driver of evolutionary change in plants, but many aspects of polyploidy in natural systems remain enigmatic. We argue that urban landscapes present an unprecedented opportunity to observe polyploidy in action. Integrating polyploid biology and urban evolutionary ecology, we discuss multiple factors expected to promote polyploid formation, establishment, and persistence in urban systems. We develop a predictive framework for the contemporary ecology and evolution of polyploid plants in cities, and through this novel perspective propose that studying polyploidy in an urban context could lead to breakthroughs in understanding fundamental processes in polyploid evolution. We conclude by highlighting the potential consequences of polyploidy in urban environments, and outline a roadmap for research into this currently unexplored field.

Realization of Lodging Tolerance in the Aromatic Grass, Cymbopogon khasianus Through Ploidy Intervention

Artificial polyploidy that brings about increase in cell size confers changes in histo-morphology leading to altered phenotype, causing changes in physiological attributes and enhanced concentration of secondary metabolites. The altered phenotype is generally a manifestation of tissue hardiness reflected as robust plant type. Based on a case study undertaken on an industrially important grass, Cymbopogon khasianus (2n = 60) valued for its citral rich essential oil, here we report that the artificial polyploidy not only brings about enhancement in concentration of essential oil but also facilitates lodging tolerance. The latter is contributed by ploidy mediated changes that occur to the cells and tissues in various plant organs by way of increased wall thickening, tissue enhancement and epidermal depositions that enable robust features. An exhaustive illustrated account covering various micro-/macro-morphological, skeletal and histochemical features constituting growth and development vis-a-vis ploidy mediated changes is presented highlighting the novelties realized on account of induced polyploidy.

Genetic Variability in Balkan Paleoendemic Resurrection Plants Ramonda serbica and R. nathaliae Across Their Range and in the Zone of Sympatry

The genus Ramonda includes three Paleoendemic and Tertiary relict species that survived in refugial habitats of the Balkan Peninsula (R. nathaliae and R. serbica) and the Iberian Peninsula (R. myconi). They are all "resurrection plants," a rare phenomenon among flowering plants in Europe. Ramonda myconi and R. nathaliae are diploids (2n = 2x = 48), while R. serbica is a hexaploid (2n = 6x = 144). The two Balkan species occur in sympatry in only two localities in eastern Serbia, where tetraploid potential hybrids (2n = 4x = 96) were found. This observation raised questions about the existence of gene flow between the two species and, more generally, about the evolutionary processes shaping their genetic diversity. To address this question, genetic markers (AFLP) and an estimate of genome size variation were used in a much larger sample and at a larger geographic scale than previously. The combination of AFLP markers and genome size results suggested ongoing processes of interspecific and interploidy hybridization in the two sites of sympatry. The data also showed that interspecific gene flow was strictly confined to sympatry. Elsewhere, both Ramonda species were characterized by low genetic diversity within populations and high population differentiation. This is consistent with the fact that the two species are highly fragmented into small and isolated populations, likely a consequence of their postglacial history. Within sympatry, enormous variability in cytotypes was observed, exceeding most reported cases of mixed ploidy in complex plant species (from 2x to >8x). The AFLP profiles of non-canonical ploidy levels indicated a diversity of origin pathways and that backcrosses probably occur between tetraploid interspecific hybrids and parental species. The question arises whether this diversity of cytotypes corresponds to a transient situation. If not, the question arises as to the genetic and ecological mechanisms that allow this diversity to be maintained over time.

Enhanced Photosynthetic Capacity, Osmotic Adjustment and Antioxidant Defenses Contribute to Improve Tolerance to Moderate Water Deficit and Recovery of Triploid Citrus Genotypes

Currently, drought stress is a major issue for crop productivity, and future climate models predict a rise in frequency and severity of drought episodes. Polyploidy has been related to improved tolerance of plants to environmental stresses. In Citrus breeding programs, the use of triploidy is an effective way to produce seedless fruits, one of the greatest consumer expectations. The current study used physiological and biochemical parameters to assess the differential responses to moderate water deficit of 3x genotypes compared to 2x genotypes belonging to the same hybridization. Both parents, the mandarin Fortune and Ellendale tangor, were also included in the experimental design, while the 2x common clementine tree was used as reference. Water deficit affects leaf water status, as well as physiological and detoxification processes. Triploid genotypes showed a better ability to maintain water status through increased proline content and photosynthetic capacity. Moreover, less oxidative damage was associated with stronger antioxidant defenses in triploid genotypes. We also found that triploidy improved the recovery capacity after a water deficit episode.

New Insights Into the Evolution of C4 Photosynthesis Offered by the Tarenaya Cluster of Cleomaceae

Cleomaceae is closely related to Brassicaceae and includes C3, C3-C4, and C4 species. Thus, this family represents an interesting system for studying the evolution of the carbon concentrating mechanism. However, inadequate genetic information on Cleomaceae limits their research applications. Here, we characterized 22 Cleomaceae accessions [3 genera (Cleoserrata, Gynandropsis, and Tarenaya) and 11 species] in terms of genome size; molecular phylogeny; as well as anatomical, biochemical, and photosynthetic traits. We clustered the species into seven groups based on genome size. Interestingly, despite clear differences in genome size (2C, ranging from 0.55 to 1.3 pg) in Tarenaya spp., this variation was not consistent with phylogenetic grouping based on the internal transcribed spacer (ITS) marker, suggesting the occurrence of multiple polyploidy events within this genus. Moreover, only G. gynandra, which possesses a large nuclear genome, exhibited the C4 metabolism. Among the C3-like species, we observed intra- and interspecific variation in nuclear genome size as well as in biochemical, physiological, and anatomical traits. Furthermore, the C3-like species had increased venation density and bundle sheath cell size, compared to C4 species, which likely predisposed the former lineages to C4 photosynthesis. Accordingly, our findings demonstrate the potential of Cleomaceae, mainly members of Tarenaya, in offering novel insights into the evolution of C4 photosynthesis.

Polyploidy but Not Range Size Is Associated With Seed and Seedling Traits That Affect Performance of Pomaderris Species

Ploidy and species range size or threat status have been linked to variation in phenotypic and phenological seed and seedling traits, including seed size, germination rate (speed) and seedling stature. There is surprisingly little known about the ecological outcomes of relationships between ploidy, key plant traits and the drivers of range size. Here we determined whether ploidy and range size in Pomaderris, a genus of shrubs that includes many threatened species, are associated with variation in seed and seedling traits that might limit the regeneration performance of obligate seeders in fire-prone systems. We experimentally quantified seed dormancy and germination processes using fire-related heat treatments and evaluated seedling performance under drought stress. We also examined the association of seed size with other seed and seedling traits. Polyploids had bigger seeds, a faster germination rate and larger and taller seedlings than diploids. There was a lack of any clear relationship between range size and seed or seedling traits. The ploidy effects observed for many traits are likely to be indirect and associated with the underlying seed size differences. These findings indicate that there is a higher potential competitive advantage in polyploid than diploid Pomaderris during regeneration, a critical stage in the post-fire environment. This insight to the regeneration phase may need to be considered when planning and prioritising management of threatened species.

Impact of polyploidy on plant tolerance to abiotic and biotic stresses

Polyploidy, defined as the coexistence of three or more complete sets of chromosomes in an organism's cells, is considered as a pivotal moving force in the evolutionary history of vascular plants and has played a major role in the domestication of several crops. In the last decades, improved cultivars of economically important species have been developed artificially by inducing autopolyploidy with chemical agents. Studies on diverse species have shown that the anatomical and physiological changes generated by either natural or artificial polyploidization can increase tolerance to abiotic and biotic stresses as well as disease resistance, which may positively impact on plant growth and net production. The aim of this work is to review the current literature regarding the link between plant ploidy level and tolerance to abiotic and biotic stressors, with an emphasis on the physiological and molecular mechanisms responsible for these effects, as well as their impact on the growth and development of both natural and artificially generated polyploids, during exposure to adverse environmental conditions. We focused on the analysis of those types of stressors in which more progress has been made in the knowledge of the putative morpho-physiological and/or molecular mechanisms involved, revealing both the factors in common, as well as those that need to be addressed in future research.

Subsurface aeration of tidal wetland soils: Root-system structure and aerenchyma connectivity in Spartina (Poaceae)

Root-aerenchyma in wetland plants facilitate transport of oxygen from aboveground sources (atmosphere and photosynthesis) to belowground roots and rhizomes, where oxygen can leak out and oxygenate the otherwise anoxic soils. In salt marshes, the soil oxygenation capacity varies among different Spartina-taxa, but little is known about structural pattern and connectivity of root-aerenchyma that facilitates this gas transport. Both environmental conditions and ploidy level play a role for the root-system morphology. Root-system morphology of polyploid Spartina-taxa was studied, quantifying root-tissue volume and root-aerenchyma volume of hexaploid Spartina alterniflora, Spartina maritima, and Spartina × townsendii as well as dodecaploid Spartina anglica from different habitats. Computed tomography (CT)-scan image analysis was applied to quantify the volume of roots and aerenchyma, and to determine the root-system structure (ratio of aerenchyma to root-tissue volumes) and aerenchyma connectivity. On average, Spartina-roots accounted for 12% (v/v) and root-aerenchyma accounted for 1% (v/v) of the soil volume in the pioneer marsh. About 90% (v/v) of all roots were associated with aerenchyma. Root-system structures of S. × townsendii and S. anglica differed and showed clear responses to habitat conditions, such as flooding regime and redox potential. The development of large well-connected aerenchyma fragments were specifically shown in S. anglica and to a minor extend in S. maritima. Aerenchyma in S. alterniflora and S. × townsendii consisted only of smaller fragments. Spartina-dominated tidal marsh soils show high connectivity with the atmosphere via root-aerenchyma. The high ploidy level in S. anglica comes along with high connectivity in root-aerenchyma.

From cells to stems: the effects of primary vascular construction on drought-induced embolism in fern rhizomes

While a considerable amount of data exists on the link between xylem construction and hydraulic function, few studies have focused on resistance to drought-induced embolism of primary vasculature in herbaceous plants. Ferns rely entirely on primary xylem and display a remarkable diversity of vascular construction in their rhizomes, making them an ideal group in which to examine hydraulic structure-function relationships. New optical methods allowed us to measure vulnerability to embolism in rhizomes, which are notoriously difficult to work with. We investigated five fern species based on their diverse xylem traits at the cellular, histological, and architectural levels. To link below- and above-ground hydraulics, we then measured leaf-stem vulnerability segmentation. Overall, rhizome vulnerability to embolism was correlated most strongly with cellular but not histological or architectural traits. Interestingly, at P_6-12 , species with increased architectural dissection were actually more vulnerable to embolism, suggesting different hydraulic dynamics at low compared to high percent embolism. Importantly, leaves fully embolize before stems reach P₈₈ , suggesting strong vulnerability segmentation. This is the first study to explore the functional implications of primary vascular construction in fern rhizomes and leaf-stem vulnerability segmentation. Strong segmentation suggests that leaves protect perennial rhizomes against severe drought stress and hydraulically induced mortality.

Differences in Floral Scent and Petal Reflectance Between Diploid and Tetraploid Chamerion angustifolium

Genome duplication in plants is thought to be a route to speciation due to cytotype incompatibility. However, to reduce cross-pollination between cytotypes in animal-pollinated species, distinctive floral phenotypes, which would allow pollinator-mediated assortative mating between flowers, are also expected. Chamerion angustifolium is a Holarctic species that forms a hybrid zone between diploid and tetraploid populations in the North American Rocky Mountains. Extensive research has shown that these cytotypes differ in many ways, including some floral traits, and that pollinators can discriminate between cytotypes, leading to assortative mating. However, two signals commonly used by insect pollinators have not been measured for this species, namely petal colour and floral scent. Using greenhouse-grown diploids and tetraploids of C. angustifolium from the ploidy hybrid-zone in the North American Rocky Mountains, we show that both floral scent signals and petal reflectance differ between cytotypes. These differences, along with differences in flower size shown previously, could help explain pollinator-mediated assortative mating observed in previous studies. However, these differences in floral phenotypes may vary in importance to pollinators. While the differences in scent included common floral volatiles readily detected by bumblebees, the differences in petal reflectance may not be perceived by bees based on their visual sensitivity across the spectra. Thus, our results suggest that differences in floral volatile emissions are more likely to contribute to pollinator discrimination between cytotypes and highlight the importance of understanding the sensory systems of pollinators when examining floral signals.

Exploring environmental selection on genome size in angiosperms

Angiosperms show a remarkable range in genome size (GS), yet most species have small genomes, despite the frequency of polyploidy and repeat amplification in the ancestries of most lineages. It has been suggested that larger genomes incur costs that have driven selection for GS reduction, although the nature of these costs and how they might impact selection remain unclear. We explore potential costs of increased GS encompassing impacts on minimum cell size with consequences for photosynthesis and water-use efficiency and effects of greater nitrogen and phosphorus demands of the nucleus leading to more severe trade-offs with photosynthesis. We suggest that nutrient-, water-, and/or CO₂-stressed conditions might favour species with smaller genomes, with implications for species' ecological and evolutionary dynamics.

Changes in ploidy affect vascular allometry and hydraulic function in Mangifera indica trees

The enucleated vascular elements of the xylem and the phloem offer an excellent system to test the effect of ploidy on plant function because variation in vascular geometry has a direct influence on transport efficiency. However, evaluations of conduit sizes in polyploid plants have remained elusive, most remarkably in woody species. We used a combination of molecular, physiological and microscopy techniques to model the hydraulic resistance between source and sinks in tetraploid and diploid mango trees. Tetraploids exhibited larger chloroplasts, mesophyll cells and stomatal guard cells, resulting in higher leaf elastic modulus and lower dehydration rates, despite the high water potentials of both ploidies in the field. Both the xylem and the phloem displayed a scaling of conduits with ploidy, revealing attenuated hydraulic resistance in tetraploids. Conspicuous wall hygroscopic moieties in the cells involved in transpiration and transport indicate a role in volumetric adjustments as a result of turgor change in both ploidies. In autotetraploids, the enlargement of organelles, cells and tissues, which are critical for water and photoassimilate transport at long distances, point to major physiological novelties associated with whole-genome duplication.

Application-based guidelines for best practices in plant flow cytometry

Flow cytometry (FCM) is currently the most widely-used method to establish nuclear DNA content in plants. Since simple, 1-3-parameter, flow cytometers, which are sufficient for most plant applications, are commercially available at a reasonable price, the number of laboratories equipped with these instruments, and consequently new FCM users, has greatly increased over the last decade. This paper meets an urgent need for comprehensive recommendations for best practices in FCM for different plant science applications. We discuss advantages and limitations of establishing plant ploidy, genome size, DNA base composition, cell cycle activity, and level of endoreduplication. Applications of such measurements in plant systematics, ecology, molecular biology research, reproduction biology, tissue cultures, plant breeding, and seed sciences are described. Advice is included on how to obtain accurate and reliable results, as well as how to manage troubleshooting that may occur during sample preparation, cytometric measurements, and data handling. Each section is followed by best practice recommendations; tips as to what specific information should be provided in FCM papers are also provided.

The role of genome duplication in big sagebrush growth and fecundity

PREMISE

Adaptive traits can be dramatically altered by genome duplication. The study of interactions among traits, ploidy, and the environment are necessary to develop an understanding of how polyploidy affects niche differentiation and to develop restoration strategies for resilient native ecosystems.

METHODS

Growth and fecundity were measured in common gardens for 39 populations of big sagebrush (Artemisia tridentata) containing two subspecies and two ploidy levels. General linear mixed-effect models assessed how much of the trait variation could be attributed to genetics (i.e., ploidy and climatic adaptation), environment, and gene-environment interactions.

RESULTS

Growth and fecundity variation were explained well by the mixed models (80% and 91%, respectively). Much of the trait variation was attributed to environment, and 15% of variation in growth and 34% of variation in seed yield were attributed to genetics. Genetic trait variation was mostly attributable to ploidy, with much higher growth and seed production in diploids, even in a warm-dry environment typically dominated by tetraploids. Population-level genetic variation was also evident and was related to the climate of each population's origin.

CONCLUSIONS

Ploidy is a strong predictor growth and seed yield, regardless of common-garden environment. The superior growth and fecundity of diploids across environments raises the question as to how tetraploids can be more prevalent than diploids, especially in warm-dry environments. Two hypotheses that may explain the abundance of tetraploids on the landscape include selection for drought resistance at the seedling stage, and greater competitive ability in water uptake in the upper soil horizon.

Phenotypic diploidization in plant functional traits uncovered by synthetic neopolyploids in Dianthus broteri

Whole-genome duplication and post-polyploidization genome downsizing play key roles in the evolution of land plants; however, the impact of genomic diploidization on functional traits still remains poorly understood. Using Dianthus broteri as a model, we compared the ecophysiological behaviour of colchicine-induced neotetraploids (4xNeo) to diploids (2x) and naturally occurring tetraploids (4xNat). Leaf gas-exchange and chlorophyll fluorescence analyses were performed in order to asses to what extent post-polyploidization evolutionary processes have affected 4xNat. Genomic diploidization and phenotypic novelty were evident. Distinct patterns of variation revealed that post-polyploidization processes altered the phenotypic shifts directly mediated by genome doubling. The photosynthetic phenotype was affected in several ways but the main effect was phenotypic diploidization (i.e. 2x and 4xNat were closer to each other than to 4xNeo). Overall, our results show the potential benefits of considering experimentally synthetized versus naturally established polyploids when exploring the role of polyploidization in promoting functional divergence.

Interspecific and intraspecific phenotypic diversity for drought adaptation in bioenergy Arundo species

Biomass crops are commonly grown in low-grade land and selection of drought-tolerant accessions is of major importance to sustain productivity. In this work, we assess phenotypic variation under different environmental scenarios in a series of accessions of Arundo donax, and contrast it with two closely related species, Arundo donaciformis and Arundo plinii. Gas-exchange and stomatal anatomy analysis showed an elevated photosynthetic capacity in A. plinii compared to A. donax and A. donaciformis with a significant intraspecific variation in A. donax. The three species showed significantly contrasting behaviour of transpiration under developing water stress and increasing vapour pressure deficit (VPD), with A. donax being the most conservative while A. plinii showed an elevated degree of insensitivity to environmental cues. Under optimal conditions, A. donax had the highest estimated leaf area (projected leaf area) and plant dry weight although a significant reduction under water stress was observed for A. donax and A. donaciformis accessions while no differences were recorded for A. plinii between optimal growing conditions (well-watered [WW]) and reduced soil water availability (water-stressed [WS]). A. donax displayed a markedly conservative water use behaviour but elevated sensitivity of biomass accumulation under stress conditions. By contrast, in A. plinii, biomass and transpiration were largely insensitive to WS and increasing VPD, though biomass dry weight under optimal conditions was significantly lower than A. donax. We provide evidence of interspecific phenotypic variation within the Arundo genus while the intraspecific phenotypic plasticity may be exploited for further selection of superior clones under disadvantageous environmental conditions. The extensive trade-off between water use and biomass accumulation present in the three species under stress conditions provides a series of novel traits to be exploited in the selection of superior clones adapted to different environmental scenarios. Non-destructive approaches are provided to screen large populations for water-stress-tolerant A. donax clones.

Genome Size Covaries More Positively with Propagule Size than Adult Size: New Insights into an Old Problem

The body size and (or) complexity of organisms is not uniformly related to the amount of genetic material (DNA) contained in each of their cell nuclei ('genome size'). This surprising mismatch between the physical structure of organisms and their underlying genetic information appears to relate to variable accumulation of repetitive DNA sequences, but why this variation has evolved is little understood. Here, I show that genome size correlates more positively with egg size than adult size in crustaceans. I explain this and comparable patterns observed in other kinds of animals and plants as resulting from genome size relating strongly to cell size in most organisms, which should also apply to single-celled eggs and other reproductive propagules with relatively few cells that are pivotal first steps in their lives. However, since body size results from growth in cell size or number or both, it relates to genome size in diverse ways. Relationships between genome size and body size should be especially weak in large organisms whose size relates more to cell multiplication than to cell enlargement, as is generally observed. The ubiquitous single-cell 'bottleneck' of life cycles may affect both genome size and composition, and via both informational (genotypic) and non-informational (nucleotypic) effects, many other properties of multicellular organisms (e.g., rates of growth and metabolism) that have both theoretical and practical significance.

Polyploidy: an evolutionary and ecological force in stressful times

Polyploidy has been hypothesized to be both an evolutionary dead-end and a source for evolutionary innovation and species diversification. Although polyploid organisms, especially plants, abound, the apparent nonrandom long-term establishment of genome duplications suggests a link with environmental conditions. Whole-genome duplications seem to correlate with periods of extinction or global change, while polyploids often thrive in harsh or disturbed environments. Evidence is also accumulating that biotic interactions, for instance, with pathogens or mutualists, affect polyploids differently than nonpolyploids. Here, we review recent findings and insights on the effect of both abiotic and biotic stress on polyploids versus nonpolyploids and propose that stress response in general is an important and even determining factor in the establishment and success of polyploidy.

Pollinator assemblage and pollen load differences on sympatric diploid and tetraploid cytotypes of the desert-dominant Larrea tridentata

PREMISE

Whole-genome duplication (polyploidy) is an important force shaping flowering-plant evolution. Ploidy-specific plant-pollinator interactions represent important community-level biotic interactions that can lead to nonrandom mating and the persistence of mixed-ploidy populations.

METHODS

At a naturally occurring diploid-tetraploid contact zone of the autopolyploid desert shrub Larrea tridentata, we combined flower phenology analyses, collections of bees on plants of known cytotype, and flow cytometry analyses of bee-collected pollen loads to investigate whether (1) diploid and tetraploid plants have unique bee pollinator assemblages, (2) bee taxa exhibit ploidy-specific visitation and pollen collection biases, and (3) specialist and generalist bee taxa have ploidy-specific visitation and pollen collection biases.

RESULTS

Although bee assemblages overlapped, we found significant differences in bee visitation to co-occurring diploids and tetraploids, with the introduced honeybee (Apis mellifera) and one native species (Andrena species 12) more frequently visiting tetraploids. Consistent with bee assemblage differences, we found that diploid pollen was overrepresented among pollen loads on native bees, while pollen loads on A. mellifera did not deviate from the random expectation. However, mismatches between the ploidy of pollen loads and plants were common, consistent with ongoing intercytotype gene flow.

CONCLUSIONS

Our data are consistent with cytotype-specific bee visitation and suggest that pollinator behavior contributes to reduced diploid-tetraploid mating. Differences in bee visitation and pollen movement potentially contribute to an easing of minority cytotype exclusion and the facilitation of cytotype co-occurrence.

Angiosperms at the edge: Extremity, diversity, and phylogeny

A hallmark of flowering plants is their ability to invade some of the most extreme and dynamic habitats, including cold and dry biomes, to a far greater extent than other land plants. Recent work has provided insight to the phylogenetic distribution and evolutionary mechanisms which have enabled this success, yet needed is a synthesis of evolutionary perspectives with plant physiological traits, morphology, and genomic diversity. Linking these disparate components will not only lead to better understand the evolutionary parallelism and diversification of plants with these two strategies, but also to provide the framework needed for directing future research. We summarize the primary physiological and structural traits involved in response to cold- and drought stress, outline the phylogenetic distribution of these adaptations, and describe the recurring association of these changes with rapid diversification events that occurred in multiple lineages over the past 15 million years. Across these threefold facets of dry-cold correlation (traits, phylogeny, and time) we stress the contrast between (a) the amazing diversity of solutions flowering plants have developed in the face of extreme environments and (b) a broad correlation between cold and dry adaptations that in some cases may hint at deep common origins.