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Shamrov II. Endosperm Development Traits in a Comparative Analysis of Endospermogenesis and Embryogenesis in Angiosperms. DOKLADY BIOLOGICAL SCIENCES : PROCEEDINGS OF THE ACADEMY OF SCIENCES OF THE USSR, BIOLOGICAL SCIENCES SECTIONS 2022; 506:239-255. [PMID: 36301432 DOI: 10.1134/s0012496622050143] [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: 09/28/2021] [Revised: 10/22/2021] [Accepted: 11/16/2021] [Indexed: 06/16/2023]
Abstract
The article discusses the fertilization process, the nucleus position in the primary cell, specifics of early endosperm development, and the principles of its classification. A new, refined classification was proposed for endosperm development modes to include three hierarchic levels: types, subtypes, and variations. Two types were distinguished by the morphogenetic potentials of the micropylar and chalazal primary cells: cellular (karyokinesis is completed with cytokinesis in both cells) and helobial (only karyokinesis takes place in both cells, and the chalazal cell sometimes remains mononucleate). The nuclear endosperm was considered as a subtype of the helobial type. Subtypes were isolated by the extent to which the micropylar and chalazal cells are involved in forming the endosperm. Variations were recognized within the subtypes by the position of walls during the tetrad or triad formation in the cellular endosperm or the number of nuclei in the chalazal cell in the helobial endosperm. The types of embryogenesis are possible to compare with subtypes or even variations of the cellular endosperm type in a comparative analysis of flowering plants, and both of the traits (the contribution of micropylar and chalazal cell derivatives to the endosperm formation and the pattern of primary cell division with the form of the tetrad) should be considered together. Two subtypes and two variations are possible to consider for the helobial endosperm.
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Affiliation(s)
- I I Shamrov
- Herzen Russian State Pedagogical University, St. Petersburg, Russia.
- Komarov Botanical Institute , Russian Academy of Sciences, St. Petersburg, Russia.
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Dalziell EL, Baskin CC, Baskin JM, Young RE, Dixon KW, Merritt DJ. Morphophysiological dormancy in the basal angiosperm order Nymphaeales. ANNALS OF BOTANY 2019; 123:95-106. [PMID: 30052753 PMCID: PMC6344092 DOI: 10.1093/aob/mcy142] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Accepted: 07/04/2018] [Indexed: 06/08/2023]
Abstract
BACKGROUND AND AIMS Substantial evidence supports the hypothesis that morphophysiological dormancy (MPD) is the basal kind of seed dormancy in the angiosperms. However, only physiological dormancy (PD) is reported in seeds of the ANA-grade genus Nymphaea. The primary aim of this study was to determine the kind of dormancy in seeds of six species of Nymphaea from the wet-dry tropics of Australia. METHODS The effects of temperature, light and germination stimulants on germination were tested on multiple collections of seeds of N. immutabilis, N. lukei, N. macrosperma, N. ondinea, N. pubescens and N. violacea. Embryo growth prior to hypocotyl emergence was monitored. KEY RESULTS Germination was generally <10 % after 28 d in control treatments. Germination percentage was highest at 30 or 35 °C for seeds exposed to light and treated with ethylene or in anoxic conditions in sealed vials of water, and it differed significantly between collections of N. lukei, N. macrosperma and N. violacea. Seeds of N. pubescens did not germinate under any of the conditions. Embryo growth (8-37 % in length) occurred before hypocotyl emergence (germination) in seeds of the five species that germinated. CONCLUSIONS Fresh seeds were dormant, and the amount of pregermination embryo growth in seeds of N. lukei and N. immutabilis was relatively small, while in seeds of N. macrosperma, N. ondinea and N. violacea it was relatively large. Thus, seeds of N. lukei and N. immutabilis had PD and those of N. macrosperma, N. ondinea and N. violacea had MPD. Overall, we found that seeds in the most phylogenetically derived clades within Nymphaea have MPD, suggesting that PD is the most likely basal trait within the Nymphaeales. This study also highlights the broad range of dormancy types and germination strategies in the ANA-grade angiosperms.
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Affiliation(s)
- Emma L Dalziell
- Kings Park Science, Department of Biodiversity, Conservation and Attractions, Kings Park, WA, Australia
- School of Molecular and Life Sciences, Curtin University, Bentley, WA, Australia
- School of Biological Sciences, The University of Western Australia, Crawley, WA, Australia
| | - Carol C Baskin
- Department of Biology, University of Kentucky, Lexington, KY, USA
- Department of Plant and Soil Sciences, University of Kentucky, Lexington, KY, USA
| | - Jerry M Baskin
- Department of Biology, University of Kentucky, Lexington, KY, USA
| | - Renee E Young
- School of Molecular and Life Sciences, Curtin University, Bentley, WA, Australia
| | - Kingsley W Dixon
- School of Molecular and Life Sciences, Curtin University, Bentley, WA, Australia
| | - David J Merritt
- Kings Park Science, Department of Biodiversity, Conservation and Attractions, Kings Park, WA, Australia
- School of Biological Sciences, The University of Western Australia, Crawley, WA, Australia
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Villegente M, Marmey P, Job C, Galland M, Cueff G, Godin B, Rajjou L, Balliau T, Zivy M, Fogliani B, Sarramegna-Burtet V, Job D. A Combination of Histological, Physiological, and Proteomic Approaches Shed Light on Seed Desiccation Tolerance of the Basal Angiosperm Amborella trichopoda. Proteomes 2017; 5:E19. [PMID: 28788068 PMCID: PMC5620536 DOI: 10.3390/proteomes5030019] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Revised: 07/22/2017] [Accepted: 07/25/2017] [Indexed: 12/13/2022] Open
Abstract
Desiccation tolerance allows plant seeds to remain viable in a dry state for years and even centuries. To reveal potential evolutionary processes of this trait, we have conducted a shotgun proteomic analysis of isolated embryo and endosperm from mature seeds of Amborella trichopoda, an understory shrub endemic to New Caledonia that is considered to be the basal extant angiosperm. The present analysis led to the characterization of 415 and 69 proteins from the isolated embryo and endosperm tissues, respectively. The role of these proteins is discussed in terms of protein evolution and physiological properties of the rudimentary, underdeveloped, Amborella embryos, notably considering that the acquisition of desiccation tolerance corresponds to the final developmental stage of mature seeds possessing large embryos.
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Affiliation(s)
- Matthieu Villegente
- Institut des Sciences Exactes et Appliquées (EA 7484), Université de Nouvelle-Calédonie, BP R4, 98851 Nouméa, Nouvelle-Calédonie.
| | - Philippe Marmey
- Institut de recherche pour le développement (IRD), UMR Diversité, Adaptation et Développement des plantes (DIADE), BP A5, 98848 Nouméa Cedex, Nouvelle-Calédonie.
| | - Claudette Job
- Centre National de la Recherche Scientifique (CNRS), CNRS-Université Claude Bernard Lyon-Institut National des Sciences Appliquées-Bayer CropScience (UMR5240), Bayer CropScience, F-69263 Lyon CEDEX 9, France.
| | - Marc Galland
- IJPB, Institut Jean-Pierre Bourgin (Institut National de la Rechercherche Agronomique(INRA), AgroParisTech, CNRS, Université Paris-Saclay) ; « Saclay Plant Sciences (SPS) » - RD10, F-78026 Versailles, France.
| | - Gwendal Cueff
- IJPB, Institut Jean-Pierre Bourgin (Institut National de la Rechercherche Agronomique(INRA), AgroParisTech, CNRS, Université Paris-Saclay) ; « Saclay Plant Sciences (SPS) » - RD10, F-78026 Versailles, France.
- AgroParisTech, Département « Science de la Vie et Santé », Unité de Formation-Recherche en Physiologie végétale, F-75231 Paris, France.
| | - Béatrice Godin
- IJPB, Institut Jean-Pierre Bourgin (Institut National de la Rechercherche Agronomique(INRA), AgroParisTech, CNRS, Université Paris-Saclay) ; « Saclay Plant Sciences (SPS) » - RD10, F-78026 Versailles, France.
- AgroParisTech, Département « Science de la Vie et Santé », Unité de Formation-Recherche en Physiologie végétale, F-75231 Paris, France.
| | - Loïc Rajjou
- IJPB, Institut Jean-Pierre Bourgin (Institut National de la Rechercherche Agronomique(INRA), AgroParisTech, CNRS, Université Paris-Saclay) ; « Saclay Plant Sciences (SPS) » - RD10, F-78026 Versailles, France.
- AgroParisTech, Département « Science de la Vie et Santé », Unité de Formation-Recherche en Physiologie végétale, F-75231 Paris, France.
| | - Thierry Balliau
- Plateforme d'Analyse Protéomique de Paris Sud Ouest (PAPPSO), GQE-Le Moulon, INRA, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, F-91190 Gif-sur-Yvette, France.
| | - Michel Zivy
- Plateforme d'Analyse Protéomique de Paris Sud Ouest (PAPPSO), GQE-Le Moulon, INRA, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, F-91190 Gif-sur-Yvette, France.
| | - Bruno Fogliani
- Institut des Sciences Exactes et Appliquées (EA 7484), Université de Nouvelle-Calédonie, BP R4, 98851 Nouméa, Nouvelle-Calédonie.
- Institut Agronomique Néo-Calédonien (IAC), Équipe ARBOREAL, Agriculture Biodiversité et Valorisation, BP 73 Port Laguerre, 98890 Païta, Nouvelle-Calédonie.
| | - Valérie Sarramegna-Burtet
- Institut des Sciences Exactes et Appliquées (EA 7484), Université de Nouvelle-Calédonie, BP R4, 98851 Nouméa, Nouvelle-Calédonie.
| | - Dominique Job
- Centre National de la Recherche Scientifique (CNRS), CNRS-Université Claude Bernard Lyon-Institut National des Sciences Appliquées-Bayer CropScience (UMR5240), Bayer CropScience, F-69263 Lyon CEDEX 9, France.
- AgroParisTech, Département « Science de la Vie et Santé », Unité de Formation-Recherche en Physiologie végétale, F-75231 Paris, France.
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Losada JM, Bachelier JB, Friedman WE. Prolonged embryogenesis in Austrobaileya scandens (Austrobaileyaceae): its ecological and evolutionary significance. THE NEW PHYTOLOGIST 2017. [PMID: 28631322 DOI: 10.1111/nph.14621] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The embryology of basal angiosperm lineages (Amborella, Nymphaeales and Austrobaileyales) is central to reconstructing the early evolution of flowering plants. Previous studies have shown that mature seeds in Austrobaileyales are albuminous, with a small embryo surrounded by a substantial diploid endosperm. However, little is known of seed ontogeny and seedling germination in Austrobaileya scandens, sister to all other extant Austrobaileyales. Standard histochemical techniques were used to study ovule/seed development and germination of Austrobaileya. Early development of the endosperm in Austrobaileya is ab initio cellular with pronounced cell proliferation. The nucellus transiently accumulates some starch, but is obliterated by expansion of a massive endosperm, where all embryo-nourishing reserves are ultimately stored. Twelve months elapse from fertilization to fruit abscission. Seeds are dispersed with a minute embryo, requiring 12 additional months for seedling establishment. The 2 yr required for seedling establishment is an apomorphic feature of Austrobaileya, probably related to germination in extremely dark understory conditions. Remarkably, although Austrobaileya seeds are nearly 50 times larger (by length) than the smallest seeds of extinct and extant members of early divergent angiosperm lineages, the embryo to seed ratio (E : S) falls squarely within the narrow range that characterizes the albuminous seeds of ancient flowering plant lineages.
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Affiliation(s)
- Juan M Losada
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA
- Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA, 02131, USA
| | - Julien B Bachelier
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA
- Institute of Biology, Structural and Functional Plant Diversity Group, Freie Universität Berlin, Altensteinstrasse 6, Berlin, 14195, Germany
| | - William E Friedman
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA
- Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA, 02131, USA
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The CKI1 Histidine Kinase Specifies the Female Gametic Precursor of the Endosperm. Dev Cell 2016; 37:34-46. [PMID: 27046830 DOI: 10.1016/j.devcel.2016.03.009] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Revised: 02/20/2016] [Accepted: 03/08/2016] [Indexed: 12/20/2022]
Abstract
Since the discovery of double fertilization, it has been recognized that flowering plants produce two highly dimorphic female gametes, the egg cell and central cell. These give rise, respectively, to the embryo and the endosperm, a nourishing tissue unique to flowering plants. Here we show that in Arabidopsis, endosperm formation requires the CYTOKININ INDEPENDENT 1 (CKI1) histidine kinase, an activator of the cytokinin signaling pathway, which specifies central cells and restricts egg cell fate. Dimorphism of the two adjacent gametes is mechanistically established in the syncytial embryo sac by spatially restricted CKI1 expression, followed by translocation of ER-localized CKI1 protein via nuclear migration. Cell specification by CKI1 likely involves activation of the cytokinin signaling pathway mediated by histidine phosphotransferases. Ectopic CKI1 expression generates non-propagating seeds with dual fertilized endosperms and no embryos. We conclude that CKI1-directed specification of the endosperm precursor central cell results in seeds containing an embryo and an endosperm.
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Marques I, Montgomery SA, Barker MS, Macfarlane TD, Conran JG, Catalán P, Rieseberg LH, Rudall PJ, Graham SW. Transcriptome-derived evidence supports recent polyploidization and a major phylogeographic division in Trithuria submersa (Hydatellaceae, Nymphaeales). THE NEW PHYTOLOGIST 2016; 210:310-323. [PMID: 26612464 DOI: 10.1111/nph.13755] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2015] [Accepted: 10/12/2015] [Indexed: 06/05/2023]
Abstract
Relatively little is known about species-level genetic diversity in flowering plants outside the eudicots and monocots, and it is often unclear how to interpret genetic patterns in lineages with whole-genome duplications. We addressed these issues in a polyploid representative of Hydatellaceae, part of the water-lily order Nymphaeales. We examined a transcriptome of Trithuria submersa for evidence of recent whole-genome duplication, and applied transcriptome-derived microsatellite (expressed-sequence tag simple-sequence repeat (EST-SSR)) primers to survey genetic variation in populations across its range in mainland Australia. A transcriptome-based Ks plot revealed at least one recent polyploidization event, consistent with fixed heterozygous genotypes representing underlying sets of homeologous loci. A strong genetic division coincides with a trans-Nullarbor biogeographic boundary. Patterns of 'allelic' variation (no more than two variants per EST-SSR genotype) and recently published chromosomal evidence are consistent with the predicted polyploidization event and substantial homozygosity underlying fixed heterozygote SSR genotypes, which in turn reflect a selfing mating system. The Nullarbor Plain is a barrier to gene flow between two deep lineages of T. submersa that may represent cryptic species. The markers developed here should also be useful for further disentangling species relationships, and provide a first step towards future genomic studies in Trithuria.
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Affiliation(s)
- Isabel Marques
- Department of Botany, University of British Columbia, 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada
- UBC Botanical Garden & Centre for Plant Research, University of British Columbia, 6804 Marine Drive SW, Vancouver, BC, V6T 1Z4, Canada
- Department of Agricultural and Environmental Sciences, High Polytechnic School of Huesca, University of Zaragoza, C/Carretera de Cuarte Km 1, Huesca, E22071, Spain
| | - Sean A Montgomery
- Department of Botany, University of British Columbia, 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada
- UBC Botanical Garden & Centre for Plant Research, University of British Columbia, 6804 Marine Drive SW, Vancouver, BC, V6T 1Z4, Canada
| | - Michael S Barker
- Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721, USA
| | - Terry D Macfarlane
- Western Australian Herbarium, Science and Conservation Division, Department of Parks and Wildlife, Locked Bag 104, Bentley Delivery Centre, Bentley, WA, 6983, Australia
| | - John G Conran
- School of Biological Sciences, Australian Centre for Evolutionary Biology and Biodiversity & Sprigg Geobiology Centre, The University of Adelaide, Benham Bldg DX 650 312, Adelaide, SA, 5005, Australia
| | - Pilar Catalán
- Department of Agricultural and Environmental Sciences, High Polytechnic School of Huesca, University of Zaragoza, C/Carretera de Cuarte Km 1, Huesca, E22071, Spain
- Department of Botany, Institute of Biology, Tomsk State University, Lenin Av. 36, Tomsk, 634050, Russia
| | - Loren H Rieseberg
- Department of Botany, University of British Columbia, 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada
| | - Paula J Rudall
- Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AB, UK
| | - Sean W Graham
- Department of Botany, University of British Columbia, 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada
- UBC Botanical Garden & Centre for Plant Research, University of British Columbia, 6804 Marine Drive SW, Vancouver, BC, V6T 1Z4, Canada
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Povilus RA, Losada JM, Friedman WE. Floral biology and ovule and seed ontogeny of Nymphaea thermarum, a water lily at the brink of extinction with potential as a model system for basal angiosperms. ANNALS OF BOTANY 2015; 115:211-26. [PMID: 25497514 PMCID: PMC4551091 DOI: 10.1093/aob/mcu235] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
BACKGROUND AND AIMS Nymphaea thermarum is a member of the Nymphaeales, of one of the most ancient lineages of flowering plants. This species was only recently described and then declared extinct in the wild, so little is known about its reproductive biology. In general, the complete ontogeny of ovules and seeds is not well documented among species of Nymphaea and has never been studied in the subgenus Brachyceras, the clade to which N. thermarum belongs. METHODS Flowers and fruits were processed for brightfield, epifluorescence and confocal microscopy. Flower morphology, with emphasis on the timing of male and female functions, was correlated with key developmental stages of the ovule and the female gametophyte. Development of the seed tissues and dynamics of polysaccharide reserves in the endosperm, perisperm and embryo were examined. KEY RESULTS Pollen release in N. thermarum starts before the flower opens. Cell walls of the micropylar nucellus show layering of callose and cellulose in a manner reminiscent of transfer cell wall patterning. Endosperm development is ab initio cellular, with micropylar and chalazal domains that embark on distinct developmental trajectories. The surrounding maternal perisperm occupies the majority of seed volume and accumulates starch centrifugally. In mature seeds, a minute but fully developed embryo is surrounded by a single, persistent layer of endosperm. CONCLUSIONS Early male and female function indicate that N. thermarum is predisposed towards self-pollination, a phenomenon that is likely to have evolved multiple times within Nymphaea. While formation of distinct micropylar and chalazal developmental domains in the endosperm, along with a copious perisperm, characterize the seeds of most members of the Nymphaeales, seed ontogenies vary between and among the constituent families. Floral biology, life history traits and small genome size make N. thermarum uniquely promising as an early-diverging angiosperm model system for genetic and molecular studies.
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Affiliation(s)
- Rebecca A Povilus
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA and Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131, USA
| | - Juan M Losada
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA and Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131, USA Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA and Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131, USA
| | - William E Friedman
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA and Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131, USA Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA and Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131, USA
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Reconstructing the age and historical biogeography of the ancient flowering-plant family Hydatellaceae (Nymphaeales). BMC Evol Biol 2014; 14:102. [PMID: 24884487 PMCID: PMC4030046 DOI: 10.1186/1471-2148-14-102] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Accepted: 05/01/2014] [Indexed: 12/26/2022] Open
Abstract
Background The aquatic flowering-plant family Hydatellaceae has a classic Gondwanan distribution, as it is found in Australia, India and New Zealand. To shed light on the biogeographic history of this apparently ancient branch of angiosperm phylogeny, we dated the family in the context of other seed-plant divergences, and evaluated its biogeography using parsimony and likelihood methods. We also explicitly tested the effect of different extinction rates on biogeographic inferences. Results We infer that the stem lineage of Hydatellaceae originated in the Lower Cretaceous; in contrast, its crown originated much more recently, in the early Miocene, with the bulk of its diversification after the onset of the Pliocene. Biogeographic reconstructions predict a mix of dispersal and vicariance events, but considerations of geological history preclude most vicariance events, besides a split at the root of the family between southern and northern clades. High extinction rates are plausible in the family, and when these are taken into account there is greater uncertainty in biogeographic inferences. Conclusions A stem origin for Hydatellaceae in the Lower Cretaceous is consistent with the initial appearance of fossils attributed to its sister clade, the water lilies. In contrast, the crown clade is young, indicating that vicariant explanations for species outside Australia are improbable. Although long-distance dispersal is likely the primary driver of biogeographic distribution in Hydatellaceae, we infer that the recent drying out of central Australia divided the family into tropical vs. subtropical/temperate clades around the beginning of the Miocene.
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Seago JL, Fernando DD. Anatomical aspects of angiosperm root evolution. ANNALS OF BOTANY 2013; 112:223-38. [PMID: 23299993 PMCID: PMC3698381 DOI: 10.1093/aob/mcs266] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2012] [Accepted: 11/09/2012] [Indexed: 05/19/2023]
Abstract
BACKGROUND AND AIMS Anatomy had been one of the foundations in our understanding of plant evolutionary trends and, although recent evo-devo concepts are mostly based on molecular genetics, classical structural information remains useful as ever. Of the various plant organs, the roots have been the least studied, primarily because of the difficulty in obtaining materials, particularly from large woody species. Therefore, this review aims to provide an overview of the information that has accumulated on the anatomy of angiosperm roots and to present possible evolutionary trends between representatives of the major angiosperm clades. SCOPE This review covers an overview of the various aspects of the evolutionary origin of the root. The results and discussion focus on angiosperm root anatomy and evolution covering representatives from basal angiosperms, magnoliids, monocots and eudicots. We use information from the literature as well as new data from our own research. KEY FINDINGS The organization of the root apical meristem (RAM) of Nymphaeales allows for the ground meristem and protoderm to be derived from the same group of initials, similar to those of the monocots, whereas in Amborellales, magnoliids and eudicots, it is their protoderm and lateral rootcap which are derived from the same group of initials. Most members of Nymphaeales are similar to monocots in having ephemeral primary roots and so adventitious roots predominate, whereas Amborellales, Austrobaileyales, magnoliids and eudicots are generally characterized by having primary roots that give rise to a taproot system. Nymphaeales and monocots often have polyarch (heptarch or more) steles, whereas the rest of the basal angiosperms, magnoliids and eudicots usually have diarch to hexarch steles. CONCLUSIONS Angiosperms exhibit highly varied structural patterns in RAM organization; cortex, epidermis and rootcap origins; and stele patterns. Generally, however, Amborellales, magnoliids and, possibly, Austrobaileyales are more similar to eudicots, and the Nymphaeales are strongly structurally associated with the monocots, especially the Acorales.
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Affiliation(s)
- James L Seago
- Department of Biological Sciences, SUNY at Oswego, Oswego, NY 13126, USA.
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Friedman WE, Bachelier JB. Seed development in Trimenia (Trimeniaceae) and its bearing on the evolution of embryo-nourishing strategies in early flowering plant lineages. AMERICAN JOURNAL OF BOTANY 2013; 100:906-915. [PMID: 23624925 DOI: 10.3732/ajb.1200632] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
PREMISE OF THE STUDY Seeds of most families in the ancient angiosperm lineage Austrobaileyales produce a full-fledged genetically biparental embryo-nourishing endosperm. However, seeds of fossil and extant Trimeniaceae have been described as having a perisperm, a maternal nutrient-storing and embryo-nourishing tissue derived from the nucellus of the ovule. Because perisperm is also found in Nymphaeales, another ancient angiosperm clade, the presence of a perisperm in Trimeniaceae, if confirmed, would be congruent with the hypothesis that the first angiosperms used a perisperm in addition to a minute (nutrient-transferring) endosperm. • METHODS Seed development was studied from fertilization through maturity/dormancy in Trimenia moorei and in maturing fruits of T. neocaledonica. • KEY RESULTS A persistent layer of nucellar tissue surrounds the endosperm but does not contain stored nutrients and does not function as a perisperm. The nutrient-storing and embryo-nourishing tissue in Trimenia seeds is an endosperm, as is the case in all other members of the Austrobaileyales studied to date. • CONCLUSION The absence of a perisperm and the presence of a typical nutrient-storing and embryo-nourishing endosperm in Trimeniaceae may represent the ancestral condition for angiosperms. However, the combination of a copious nutrient-storing and embryo-nourishing perisperm with a minute endosperm, as in Nymphaeales, remains a plausible plesiomorphic condition for angiosperms as a whole. In either case, the developmental and functional biology of the diploid endosperm of Trimenia (and other Austrobaileyales) differs markedly from the diploid endosperm of Nymphaeales, and is fundamentally similar to the triploid endosperms of most other angiosperms.
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Affiliation(s)
- William E Friedman
- Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131, USA.
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Costa M, Pereira AM, Rudall PJ, Coimbra S. Immunolocalization of arabinogalactan proteins (AGPs) in reproductive structures of an early-divergent angiosperm, Trithuria (Hydatellaceae). ANNALS OF BOTANY 2013; 111. [PMID: 23186834 PMCID: PMC3555524 DOI: 10.1093/aob/mcs256] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
BACKGROUND AND AIMS Trithuria is the sole genus of Hydatellaceae, a family of the early-divergent angiosperm lineage Nymphaeales (water-lilies). In this study different arabinogalactan protein (AGP) epitopes in T. submersa were evaluated in order to understand the diversity of these proteins and their functions in flowering plants. METHODS Immunolabelling of different AGPs and pectin epitopes in reproductive structures of T. submersa at the stage of early seed development was achieved by immunofluorescence of specific antibodies. KEY RESULTS AGPs in Trithuria pistil tissues could be important as structural proteins and also as possible signalling molecules. Intense labelling was obtained with anti-AGP antibodies both in the anthers and in the intine wall, the latter associated with pollen tube emergence. CONCLUSIONS AGPs could play a significant role in Trithuria reproduction, due to their specific presence in the pollen tube pathway. The results agree with labellings obtained for Arabidopsis and confirms the importance of AGPs in angiosperm reproductive structures as essential structural components and probably important signalling molecules.
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Affiliation(s)
- Mário Costa
- Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Edifício FC4 Rua do Campo Alegre 4169-007 Porto, Portugal
- BioFIG, Center for Biodiversity, Functional and Integrative Genomics, Portugal
| | - Ana Marta Pereira
- Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Edifício FC4 Rua do Campo Alegre 4169-007 Porto, Portugal
- BioFIG, Center for Biodiversity, Functional and Integrative Genomics, Portugal
| | - Paula J. Rudall
- Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AAB, UK
| | - Sílvia Coimbra
- Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Edifício FC4 Rua do Campo Alegre 4169-007 Porto, Portugal
- BioFIG, Center for Biodiversity, Functional and Integrative Genomics, Portugal
- For correspondence. E-mail
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12
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Friedman WE, Bachelier JB, Hormaza JI. Embryology in Trithuria submersa (Hydatellaceae) and relationships between embryo, endosperm, and perisperm in early-diverging flowering plants. AMERICAN JOURNAL OF BOTANY 2012; 99:1083-95. [PMID: 22688427 DOI: 10.3732/ajb.1200066] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
PREMISE OF THE STUDY Despite their highly reduced morphology, Hydatellaceae bear the unmistakable embryological signature of Nymphaeales, including a starch-rich maternal perisperm and a minute biparental endosperm and embryo. The co-occurrence of perisperm and endosperm in Nymphaeales and other lineages of flowering plants, and their respective functions during the course of seed development and embryo germination, remain enigmatic. METHODS Development of the embryo, endosperm, and perisperm was examined histologically from fertilization through germination in flowers and fruits of Trithuria submersa. KEY RESULTS The embryo of T. submersa initiates two cotyledons prior to seed maturity/dormancy, and their tips remain in contact with the endosperm throughout germination. The endosperm persists as a single layer of cells and serves as the interface between the embryo and the perisperm. The perisperm contains carbohydrates and proteins, and functions as the main storage tissue. The endosperm accumulates proteins and aleurone grains and functions as a transfer cell layer. CONCLUSIONS In Nymphaeales, the multiple roles of a more typical endosperm have been separated into two different tissues and genetic entities: a maternal perisperm (nutrient acquisition, storage, mobilization) and a minute biparental endosperm (nutrient transfer to the embryo). The presence of perisperms among several other ancient lineages of angiosperms suggests a modest degree of developmental and functional lability for the nutrient storage tissue (perisperm or endosperm) within seeds during the early evolution of flowering plants. Finally, we examine the evolutionary developmental hypothesis that, contrary to longstanding assumptions, an embryo-nourishing perisperm along with a minute endosperm may represent the plesiomorphic condition for flowering plants.
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Affiliation(s)
- William E Friedman
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138 USA.
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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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Taylor ML, Williams JH. Pollen tube development in two species of Trithuria (Hydatellaceae) with contrasting breeding systems. ACTA ACUST UNITED AC 2012; 25:83-96. [DOI: 10.1007/s00497-012-0183-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2011] [Accepted: 02/08/2012] [Indexed: 11/30/2022]
Affiliation(s)
- Mackenzie L Taylor
- Department of Biology, Creighton University, 2500 California Plaza, Omaha, NE 68178, USA.
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15
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Prychid CJ, Sokoloff DD, Remizowa MV, Tuckett RE, Yadav SR, Rudall PJ. Unique stigmatic hairs and pollen-tube growth within the stigmatic cell wall in the early-divergent angiosperm family Hydatellaceae. ANNALS OF BOTANY 2011; 108:599-608. [PMID: 21320877 PMCID: PMC3170147 DOI: 10.1093/aob/mcr021] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/24/2010] [Accepted: 01/05/2011] [Indexed: 05/07/2023]
Abstract
BACKGROUND AND AIMS The ultrastructure of the pollen tubes and the unusual multicellular stigmatic hairs of Trithuria, the sole genus of Hydatellaceae, are described in the context of comparative studies of stigmatic and transmitting tissue in other early-divergent angiosperms. METHODS Scanning and transmission electron microscopy and immunocytochemistry are used to study the structure and composition of both mature and immature stigmatic hair cells and pollen-tube growth in Trithuria. KEY RESULTS Trithuria possesses a dry-type stigma. Pollen tubes grow within the cell walls of the long multicellular stigmatic hairs. Immunocytochemistry results suggest that arabinogalactan proteins are involved in attracting the pollen tubes through the stigmatic cuticle. Most tubes grow along the hair axis towards its base, but some grow towards the hair apex, suggesting that pollen tubes are guided by both physical constraints such as microfibril orientation and the presence of binding factors such as unesterified pectins and adhesive proteins. CONCLUSIONS The presence of a dry-type stigma in Trithuria supports the hypothesis that this condition is ancestral in angiosperms. Each multicellular stigmatic hair of Hydatellaceae is morphologically homologous with a stigmatic papilla of other angiosperms, but functions as an independent stigma and style. This unusual combination of factors makes Hydatellaceae a useful model for comparative studies of pollen-tube growth in early angiosperms.
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Affiliation(s)
| | - Dmitry D. Sokoloff
- Department of Higher Plants, Biological Faculty, Moscow State University, 119991 Moscow, Russia
| | - Margarita V. Remizowa
- Department of Higher Plants, Biological Faculty, Moscow State University, 119991 Moscow, Russia
| | - Renee E. Tuckett
- University of Western Australia, Crawley, WA 6009 and Botanic Gardens and Parks Authority, Fraser Avenue, West Perth, WA 6005, Australia
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Vialette-Guiraud ACM, Alaux M, Legeai F, Finet C, Chambrier P, Brown SC, Chauvet A, Magdalena C, Rudall PJ, Scutt CP. Cabomba as a model for studies of early angiosperm evolution. ANNALS OF BOTANY 2011; 108:589-98. [PMID: 21486926 PMCID: PMC3170152 DOI: 10.1093/aob/mcr088] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2010] [Accepted: 03/02/2011] [Indexed: 05/18/2023]
Abstract
BACKGROUND The angiosperms, or flowering plants, diversified in the Cretaceous to dominate almost all terrestrial environments. Molecular phylogenetic studies indicate that the orders Amborellales, Nymphaeales and Austrobaileyales, collectively termed the ANA grade, diverged as separate lineages from a remaining angiosperm clade at a very early stage in flowering plant evolution. By comparing these early diverging lineages, it is possible to infer the possible morphology and ecology of the last common ancestor of the extant angiosperms, and this analysis can now be extended to try to deduce the developmental mechanisms that were present in early flowering plants. However, not all species in the ANA grade form convenient molecular-genetic models. SCOPE The present study reviews the genus Cabomba (Nymphaeales), which shows a range of features that make it potentially useful as a genetic model. We focus on characters that have probably been conserved since the last common ancestor of the extant flowering plants. To facilitate the use of Cabomba as a molecular model, we describe methods for its cultivation to flowering in the laboratory, a novel Cabomba flower expressed sequence tag database, a well-adapted in situ hybridization protocol and a measurement of the nuclear genome size of C. caroliniana. We discuss the features required for species to become tractable models, and discuss the relative merits of Cabomba and other ANA-grade angiosperms in molecular-genetic studies aimed at understanding the origin of the flowering plants.
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Affiliation(s)
- Aurelie C. M. Vialette-Guiraud
- Laboratoire de Reproduction et Développement des Plantes, UMR 5667, CNRS-INRA-Université de Lyon, Ecole Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon Cedex 07, France
| | - Michael Alaux
- INRA-URGI Centre de Versailles, Bâtiment 18, Route de Saint-Cyr, 78026 Versailles Cedex, France
| | - Fabrice Legeai
- UMR Bio3P, Campus de Beaulieu, 35042 Rennes Cedex, France
| | - Cedric Finet
- Laboratoire de Reproduction et Développement des Plantes, UMR 5667, CNRS-INRA-Université de Lyon, Ecole Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon Cedex 07, France
| | - Pierre Chambrier
- Laboratoire de Reproduction et Développement des Plantes, UMR 5667, CNRS-INRA-Université de Lyon, Ecole Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon Cedex 07, France
| | - Spencer C. Brown
- Institut des Sciences du Végétal CNRS UPR2355, Bâtiment 23, Avenue de la Terrasse, F-91198 Gif-sur-Yvette Cedex, France
| | - Aurelie Chauvet
- Laboratoire de Reproduction et Développement des Plantes, UMR 5667, CNRS-INRA-Université de Lyon, Ecole Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon Cedex 07, France
| | | | | | - Charles P. Scutt
- Laboratoire de Reproduction et Développement des Plantes, UMR 5667, CNRS-INRA-Université de Lyon, Ecole Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon Cedex 07, France
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Givnish TJ, Ames M, McNeal JR, McKain MR, Steele PR, dePamphilis CW, Graham SW, Pires JC, Stevenson DW, Zomlefer WB, Briggs BG, Duvall MR, Moore MJ, Heaney JM, Soltis DE, Soltis PS, Thiele K, Leebens-Mack JH. Assembling the Tree of the Monocotyledons: Plastome Sequence Phylogeny and Evolution of Poales 1. ANNALS OF THE MISSOURI BOTANICAL GARDEN 2010. [PMID: 0 DOI: 10.3417/2010023] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
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18
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Tuckett RE, Merritt DJ, Rudall PJ, Hay F, Hopper SD, Baskin CC, Baskin JM, Tratt J, Dixon KW. A new type of specialized morphophysiological dormancy and seed storage behaviour in Hydatellaceae, an early-divergent angiosperm family. ANNALS OF BOTANY 2010; 105:1053-61. [PMID: 20338953 PMCID: PMC2876005 DOI: 10.1093/aob/mcq062] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Revised: 01/25/2010] [Accepted: 02/11/2010] [Indexed: 05/22/2023]
Abstract
BACKGROUND AND AIMS Recent phylogenetic analysis has placed the aquatic family Hydatellaceae as an early-divergent angiosperm. Understanding seed dormancy, germination and desiccation tolerance of Hydatellaceae will facilitate ex situ conservation and advance hypotheses regarding angiosperm evolution. METHODS Seed germination experiments were completed on three species of south-west Australian Hydatellaceae, Trithuria austinensis, T. bibracteata and T. submersa, to test the effects of temperature, light, germination stimulant and storage. Seeds were sectioned to examine embryo growth during germination in T. austinensis and T. submersa. KEY RESULTS Some embryo growth and cell division in T. austinensis and T. submersa occurred prior to the emergence of an undifferentiated embryo from the seed coat ('germination'). Embryo differentiation occurred later, following further growth and a 3- to 4-fold increase in the number of cells. The time taken to achieve 50 % of maximum germination for seeds on water agar was 50, 35 and 37 d for T. austinensis, T bibracteata and T. submersa, respectively. CONCLUSIONS Seeds of Hydatellaceae have a new kind of specialized morphophysiological dormancy in which neither root nor shoot differentiates until after the embryo emerges from the seed coat. Seed biology is discussed in relation to early angiosperm evolution, together with ex situ conservation of this phylogenetically significant group.
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Affiliation(s)
- Renee E. Tuckett
- School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, 6009, Western Australia
- Kings Park and Botanic Garden, West Perth, 6005, Western Australia
| | - David J. Merritt
- School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, 6009, Western Australia
- Kings Park and Botanic Garden, West Perth, 6005, Western Australia
| | - Paula J. Rudall
- Jodrell Laboratory, Royal Botanic Gardens Kew, Richmond, Surrey TW9 3AB, UK
| | - Fiona Hay
- Seed Conservation Department, Royal Botanic Gardens Kew, Wakehurst Place, Ardingly, West Sussex RH17 6TN, UK
- International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines
| | - Stephen D. Hopper
- School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, 6009, Western Australia
- Royal Botanic Gardens Kew, Richmond, Surrey TW9 3AB, UK
| | - Carol C. Baskin
- Department of Biology, University of Kentucky, Lexington, KY 40506-0225, USA
- Department of Plant and Soil Sciences, University of Kentucky, Lexington, KY 40546-0312, USA.
| | - Jerry M. Baskin
- Department of Plant and Soil Sciences, University of Kentucky, Lexington, KY 40546-0312, USA.
| | - Julia Tratt
- Jodrell Laboratory, Royal Botanic Gardens Kew, Richmond, Surrey TW9 3AB, UK
| | - Kingsley W. Dixon
- School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, 6009, Western Australia
- Kings Park and Botanic Garden, West Perth, 6005, Western Australia
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Abstract
The evolution of the seed represents a remarkable life-history transition for photosynthetic organisms. Here, we review the recent literature and historical understanding of how and why seeds evolved. Answering the 'how' question involves a detailed understanding of the developmental morphology and anatomy of seeds, as well as the genetic programs that determine seed size. We complement this with a special emphasis on the evolution of dormancy, the characteristic of seeds that allows for long 'distance' time travel. Answering the 'why' question involves proposed hypotheses of how natural selection has operated to favor the seed life-history phenomenon. The recent flurry of research describing the comparative biology of seeds is discussed. The review will be divided into sections dealing with: (1) the development and anatomy of seeds; (2) the endosperm; (3) dormancy; (4) early seed-like structures and the transition to seeds; and (5) the evolution of seed size (mass). In many cases, a special distinction is made between angiosperm and gymnosperm seeds. Finally, we make some recommendations for future research in seed biology.
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Affiliation(s)
- Ada Linkies
- Botany/Plant Physiology, Institute for Biology II, Faculty of Biology, University of Freiburg, Schänzlestr. 1, D-79104 Freiburg, Germany (http://www.seedbiology.de)
| | - Kai Graeber
- Botany/Plant Physiology, Institute for Biology II, Faculty of Biology, University of Freiburg, Schänzlestr. 1, D-79104 Freiburg, Germany (http://www.seedbiology.de)
| | - Charles Knight
- Biological Sciences Department, California Polytechnic State University, San Luis Obispo, CA 93401, USA
| | - Gerhard Leubner-Metzger
- Botany/Plant Physiology, Institute for Biology II, Faculty of Biology, University of Freiburg, Schänzlestr. 1, D-79104 Freiburg, Germany (http://www.seedbiology.de)
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Rudall PJ, Bateman RM. Defining the limits of flowers: the challenge of distinguishing between the evolutionary products of simple versus compound strobili. Philos Trans R Soc Lond B Biol Sci 2010; 365:397-409. [PMID: 20047867 DOI: 10.1098/rstb.2009.0234] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Recent phylogenetic reconstructions suggest that axially condensed flower-like structures evolved iteratively in seed plants from either simple or compound strobili. The simple-strobilus model of flower evolution, widely applied to the angiosperm flower, interprets the inflorescence as a compound strobilus. The conifer cone and the gnetalean 'flower' are commonly interpreted as having evolved from a compound strobilus by extreme condensation and (at least in the case of male conifer cones) elimination of some structures present in the presumed ancestral compound strobilus. These two hypotheses have profoundly different implications for reconstructing the evolution of developmental genetic mechanisms in seed plants. If different flower-like structures evolved independently, there should intuitively be little commonality of patterning genes. However, reproductive units of some early-divergent angiosperms, including the extant genus Trithuria (Hydatellaceae) and the extinct genus Archaefructus (Archaefructaceae), apparently combine features considered typical of flowers and inflorescences. We re-evaluate several disparate strands of comparative data to explore whether flower-like structures could have arisen by co-option of flower-expressed patterning genes into independently evolved condensed inflorescences, or vice versa. We discuss the evolution of the inflorescence in both gymnosperms and angiosperms, emphasising the roles of heterotopy in dictating gender expression and heterochrony in permitting internodal compression.
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Affiliation(s)
- Paula J Rudall
- Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond Surrey TW9 3DS, UK.
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