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Burkhard Becker - One of the best experts on this subject based on the ideXlab platform.
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The Origin and Evolution of the Plant Cell Surface: Algal Integrin-Associated Proteins and a New Family of Integrin-Like Cytoskeleton-ECM Linker Proteins.
Genome Biology and Evolution, 2015Co-Authors: Burkhard Becker, Jean Michel Doan, Brandon A. Wustman, Eric J. Carpenter, Li Chen, Yong Zhang, Gane Ka-shu Wong, Michael MelkonianAbstract:The extracellular matrix of scaly green flagellates consists of small organic scales consisting of polysaccharides and scale-associated proteins (SAPs). Molecular phylogenies have shown that these organisms represent the ancestral stock of flagellates from which all green plants (Viridiplantae) evolved. The molecular characterization of four different SAPs is presented. Three SAPs are type-2 membrane proteins with an arginine/alanine-rich short cytoplasmic tail and an extracellular domain that is most likely of bacterial origin. The fourth protein is a filamin-like protein. In addition, we report the presence of proteins similar to the integrin-associated proteins α-actinin (in transcriptomes of glaucophytes and some viridiplants), LIM-domain proteins, and integrin-associated kinase in transcriptomes of viridiplants, glaucophytes, and rhodophytes. We propose that the membrane proteins identified are the predicted linkers between scales and the cytoskeleton. These proteins are present in many green algae but are apparently absent from Embryophytes. These proteins represent a new protein family we have termed gralins for green algal integrins. Gralins are absent from Embryophytes. A model for the evolution of the cell surface proteins in Plantae is discussed.
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Snow ball earth and the split of Streptophyta and Chlorophyta
Trends in Plant Science, 2012Co-Authors: Burkhard BeckerAbstract:About 700 million years ago (Mya), the ancestor of all green plants evolved into two major groups: the Chlorophyta (many green algae) and the Streptophyta (some green algae and land plants = Embryophytes). Both groups are separated by several morphological, physiological, and molecular characteristics, including different photorespiration pathways. The Chloropyhta/Streptophyta split was probably very important for the colonization of the terrestrial habitat because Embryophytes, the descendants of streptophyte algae, today completely dominate the macrophyte flora of the terrestrial habitats. By contrast, in aquatic ecosystems macrophytes from brown, red, and green algae compete with Embryophytes. In this opinion article, I argue that the Chlorophyta/Streptophyta split is related to glaciation events (snow ball earth states) in the Neoproterozoic and provide an explanation for the different photorespiration pathways.
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Origin of land plants: Do conjugating green algae hold the key?
BMC Evolutionary Biology, 2011Co-Authors: Sabina Wodniok, Gernot Glöckner, Andrew J. Heidel, Hervé Philippe, Michael Melkonian, Henner Brinkmann, Burkhard BeckerAbstract:The terrestrial habitat was colonized by the ancestors of modern land plants about 500 to 470 million years ago. Today it is widely accepted that land plants (Embryophytes) evolved from streptophyte algae, also referred to as charophycean algae. The streptophyte algae are a paraphyletic group of green algae, ranging from unicellular flagellates to morphologically complex forms such as the stoneworts (Charales). For a better understanding of the evolution of land plants, it is of prime importance to identify the streptophyte algae that are the sister-group to the Embryophytes. The Charales, the Coleochaetales or more recently the Zygnematales have been considered to be the sister group of the Embryophytes However, despite many years of phylogenetic studies, this question has not been resolved and remains controversial. Here, we use a large data set of nuclear-encoded genes (129 proteins) from 40 green plant taxa (Viridiplantae) including 21 Embryophytes and six streptophyte algae, representing all major streptophyte algal lineages, to investigate the phylogenetic relationships of streptophyte algae and Embryophytes. Our phylogenetic analyses indicate that either the Zygnematales or a clade consisting of the Zygnematales and the Coleochaetales are the sister group to Embryophytes. Our analyses support the notion that the Charales are not the closest living relatives of Embryophytes. Instead, the Zygnematales or a clade consisting of Zygnematales and Coleochaetales are most likely the sister group of Embryophytes. Although this result is in agreement with a previously published phylogenetic study of chloroplast genomes, additional data are needed to confirm this conclusion. A Zygnematales/Embryophyte sister group relationship has important implications for early land plant evolution. If substantiated, it should allow us to address important questions regarding the primary adaptations of viridiplants during the conquest of land. Clearly, the biology of the Zygnematales will receive renewed interest in the future.
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Streptophyte algae and the origin of Embryophytes
Annals of Botany, 2009Co-Authors: Burkhard Becker, Birger MarinAbstract:Land plants (Embryophytes) evolved from streptophyte green algae, a small group of freshwater algae ranging from scaly, unicellular flagellates (Mesostigma) to complex, filamentous thalli with branching, cell differentiation and apical growth (Charales). Streptophyte algae and Embryophytes form the division Streptophyta, whereas the remaining green algae are classified as Chlorophyta. The Charales (stoneworts) are often considered to be sister to land plants, suggesting progressive evolution towards cellular complexity within streptophyte green algae. Many cellular (e.g. phragmoplast, plasmodesmata, hexameric cellulose synthase, structure of flagellated cells, oogamous sexual reproduction with zygote retention) and physiological characters (e.g. type of photorespiration, phytochrome system) originated within streptophyte algae. Phylogenetic studies have demonstrated that Mesostigma (flagellate) and Chlorokybus (sarcinoid) form the earliest divergence within streptophytes, as sister to all other Streptophyta including Embryophytes. The question whether Charales, Coleochaetales or Zygnematales are the sister to Embryophytes is still (or, again) hotly debated. Projects to study genome evolution within streptophytes including protein families and polyadenylation signals have been initiated. In agreement with morphological and physiological features, many molecular traits believed to be specific for Embryophytes have been shown to predate the Chlorophyta/Streptophyta split, or to have originated within streptophyte algae. Molecular phylogenies and the fossil record allow a detailed reconstruction of the early evolutionary events that led to the origin of true land plants, and shaped the current diversity and ecology of streptophyte green algae and their Embryophyte descendants. The Streptophyta/Chlorophyta divergence correlates with a remarkably conservative preference for freshwater/marine habitats, and the early freshwater adaptation of streptophyte algae was a major advantage for the earliest land plants, even before the origin of the embryo and the sporophyte generation. The complete genomes of a few key streptophyte algae taxa will be required for a better understanding of the colonization of terrestrial habitats by streptophytes.
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EST analysis of the scaly green flagellate Mesostigma viride (Streptophyta): Implications for the evolution of green plants (Viridiplantae)
BMC Plant Biology, 2006Co-Authors: Andreas Simon, Gernot Glöckner, Michael Melkonian, Marius Felder, Burkhard BeckerAbstract:Background The Viridiplantae (land plants and green algae) consist of two monophyletic lineages, the Chlorophyta and the Streptophyta. The Streptophyta include all Embryophytes and a small but diverse group of freshwater algae traditionally known as the Charophyceae (e.g. Charales, Coleochaete and the Zygnematales). The only flagellate currently included in the Streptophyta is Mesostigma viride Lauterborn. To gain insight into the genome evolution in streptophytes, we have sequenced 10,395 ESTs from Mesostigma representing 3,300 independent contigs and compared the ESTs of Mesostigma with available plant genomes ( Arabidopsis, Oryza , Chlamydomonas ), with ESTs from the bryophyte Physcomitrella , the genome of the rhodophyte Cyanidioschyzon , the ESTs from the rhodophyte Porphyra , and the genome of the diatom Thalassiosira . Results The number of expressed genes shared by Mesostigma with the Embryophytes (90.3 % of the expressed genes showing similarity to known proteins) is higher than with Chlamydomonas (76.1 %). In general, cytosolic metabolic pathways, and proteins involved in vesicular transport, transcription, regulation, DNA-structure and replication, cell cycle control, and RNA-metabolism are more conserved between Mesostigma and the Embryophytes than between Mesostigma and Chlamydomonas . However, plastidic and mitochondrial metabolic pathways, cytoskeletal proteins and proteins involved in protein folding are more conserved between Mesostigma and Chlamydomonas than between Mesostigma and the Embryophytes. Conclusion Our EST-analysis of Mesostigma supports the notion that this organism should be a suitable unicellular model for the last flagellate common ancestor of the streptophytes. Mesostigma shares more genes with the Embryophytes than with the chlorophyte Chlamydomonas reinhardtii , although both organisms are flagellate unicells. Thus, it seems likely that several major physiological changes (e.g. in the regulation of photosynthesis and photorespiration) took place early during the evolution of streptophytes, i.e. before the transition to land.
Birger Marin - One of the best experts on this subject based on the ideXlab platform.
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genomes of subaerial zygnematophyceae provide insights into land plant evolution
Cell, 2019Co-Authors: Shifeng Cheng, Wenfei Xian, Birger Marin, Jean Keller, Tian Wu, Yuan Fu, Yan Xu, Yu Zhang, Xiuli Li, Sebastian WittekAbstract:Summary The transition to a terrestrial environment, termed terrestrialization, is generally regarded as a pivotal event in the evolution and diversification of the land plant flora that changed the surface of our planet. Through phylogenomic studies, a group of streptophyte algae, the Zygnematophyceae, have recently been recognized as the likely sister group to land plants (Embryophytes). Here, we report genome sequences and analyses of two early diverging Zygnematophyceae (Spirogloea muscicola gen. nov. and Mesotaenium endlicherianum) that share the same subaerial/terrestrial habitat with the earliest-diverging Embryophytes, the bryophytes. We provide evidence that genes (i.e., GRAS and PYR/PYL/RCAR) that increase resistance to biotic and abiotic stresses in land plants, in particular desiccation, originated or expanded in the common ancestor of Zygnematophyceae and Embryophytes, and were gained by horizontal gene transfer (HGT) from soil bacteria. These two Zygnematophyceae genomes represent a cornerstone for future studies to understand the underlying molecular mechanism and process of plant terrestrialization.
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Streptophyte algae and the origin of Embryophytes
Annals of Botany, 2009Co-Authors: Burkhard Becker, Birger MarinAbstract:Land plants (Embryophytes) evolved from streptophyte green algae, a small group of freshwater algae ranging from scaly, unicellular flagellates (Mesostigma) to complex, filamentous thalli with branching, cell differentiation and apical growth (Charales). Streptophyte algae and Embryophytes form the division Streptophyta, whereas the remaining green algae are classified as Chlorophyta. The Charales (stoneworts) are often considered to be sister to land plants, suggesting progressive evolution towards cellular complexity within streptophyte green algae. Many cellular (e.g. phragmoplast, plasmodesmata, hexameric cellulose synthase, structure of flagellated cells, oogamous sexual reproduction with zygote retention) and physiological characters (e.g. type of photorespiration, phytochrome system) originated within streptophyte algae. Phylogenetic studies have demonstrated that Mesostigma (flagellate) and Chlorokybus (sarcinoid) form the earliest divergence within streptophytes, as sister to all other Streptophyta including Embryophytes. The question whether Charales, Coleochaetales or Zygnematales are the sister to Embryophytes is still (or, again) hotly debated. Projects to study genome evolution within streptophytes including protein families and polyadenylation signals have been initiated. In agreement with morphological and physiological features, many molecular traits believed to be specific for Embryophytes have been shown to predate the Chlorophyta/Streptophyta split, or to have originated within streptophyte algae. Molecular phylogenies and the fossil record allow a detailed reconstruction of the early evolutionary events that led to the origin of true land plants, and shaped the current diversity and ecology of streptophyte green algae and their Embryophyte descendants. The Streptophyta/Chlorophyta divergence correlates with a remarkably conservative preference for freshwater/marine habitats, and the early freshwater adaptation of streptophyte algae was a major advantage for the earliest land plants, even before the origin of the embryo and the sporophyte generation. The complete genomes of a few key streptophyte algae taxa will be required for a better understanding of the colonization of terrestrial habitats by streptophytes.
John A. Raven - One of the best experts on this subject based on the ideXlab platform.
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Life at the boundary: Photosynthesis at the soil-fluid interface. A synthesis focusing on mosses
Journal of Experimental Botany, 2016Co-Authors: John A. Raven, Timothy D. ColmerAbstract:: Mosses are among the earliest branching Embryophytes and probably originated not later than the early Ordovician when atmospheric CO2 was higher and O2 was lower than today. The C3 biochemistry and physiology of their photosynthesis suggests, by analogy with tracheophytes, that growth of extant bryophytes in high CO2 approximating Ordovician values would increase the growth rate. This occurs for many mosses, including Physcomitrella patens in suspension culture, although recently published transcriptomic data on this species at high CO2 and present-day CO2 show down-regulation of the transcription of several genes related to photosynthesis. It would be useful if transcriptomic (and proteomic) data comparing growth conditions are linked to measurements of growth and physiology on the same, or parallel, cultures. Mosses (like later-originating Embryophytes) have been subject to changes in bulk atmospheric CO2 and O2 throughout their existence, with evidence, albeit limited, for positive selection of moss Rubisco. Extant mosses are subject to a large range of CO2 and O2 concentrations in their immediate environments, especially aquatic mosses, and mosses are particularly influenced by CO2 generated by, and O2 consumed by, soil chemoorganotrophy from organic C produced by tracheophytes (if present) and bryophytes.
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Photosynthesis in Early Land Plants: Adapting to the Terrestrial Environment
Advances in Photosynthesis and Respiration, 2013Co-Authors: John A. Raven, Dianne EdwardsAbstract:The embryophytic land plants evolved from charophycean green algae, one of the three clades of green algae which are important components of the microflora of present-day terrestrial habitats. The earliest Embryophytes are recognised in the fossil record from their characteristic spores, with little evidence as to their vegetative structure. These earliest Embryophytes presumably resemble the extant terrestrial green algae in being desiccation tolerant and poikilohydric. Only the embrophytes subsequently developed the homoiohydry which characterised the organism which today contribute most of the biomass and primary productivity on land, and allowed many of the organisms to become desiccation intolerant in the vegetative phase. Pre-Carboniferous land plant fossils have very few examples of bryophytes other than spores: exceptions are the Middle Devonian Metzgeriothallus and the Upper Devonian Pallaviciniites. Many of the other fossils are recognisable as polysporangiophytes, including vascular plants. Homoiohydry in some of these plants is shown by the occurrence of cuticle and stomata, although there is no fossil evidence bearing on desiccation tolerance/intolerance. In addition to the Embryophytes there are many other fossils, e.g. Pachytheca, Parka, Protosalvinia, Prototaxites and Spongiophyton, which are probably photosynthetic organisms, but are not readily classified: algae, bryophytes and lichens have been suggested, in addition to the possibility that some represent terrestrial fungi. The high atmospheric CO2 concentrations in the early Phanerozoic would have permitted higher rates of photosynthesis than occurs today on the basis of the surface area of the plant exposed to the gas phase because large concentration gradients from the atmosphere to the carboxylase driving diffusive entry of CO2 are possible. Relatively complex morphologies (several layers of photosynthetic structures) and/or anatomy (ventilation within the organisms using gas spaces) are required if the light-harvesting capacity is to be matched by the CO2 assimilation capacity.
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Physiological evolution of lower Embryophytes: Adaptations to the terrestrial environment
The Evolution of Plant Physiology, 2007Co-Authors: John A. Raven, Dianne EdwardsAbstract:Publisher Summary This chapter examines the differences in physiology among Embryophytes and their algal ancestors, with particular emphasis on their water relations. The Embryophytes have very significant variations in water relations and the chapter considers their evolution within the Embryophytes as well as the evolution of Embryophyte water relations from those of their algal ancestors. The chapter also examines the relationship of the likely evolution of Embryophyte water relations to cladistic analyses of Embryophyte phylogeny and to the fossil record. The physiological changes that occurred in the evolution from algal ancestors to the different grades of organization of Embryophytes has been determined from the physiology of extant plants in relation to their phylogeny as determined by cladistic analysis and from the order in which anatomical features appeared in the fossil record. The fossil record of Embryophytes also reveals certain characteristics of organisms that are not found today. The fossil record is not helpful in providing some information such as desiccation tolerance or intolerance, except by applying an empirical correlation from extant plants that no Embryophyte more than 1 meter in height is desiccation tolerant in the vegetative phase. Overall, lines of evidence indicate that the earliest Embryophytes were desiccation tolerant and poikilohydric.
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Selection pressures on stomatal evolution
New Phytologist, 2002Co-Authors: John A. RavenAbstract:Summary Fossil evidence shows that stomata have occurred in sporophytes and (briefly) gametophytes of Embryophytes during the last 400 m yr. Cladistic analyses with hornworts basal are consistent with a unique origin of stomata, although cladograms with hornworts as the deepest branching Embryophytes require loss of stomata early in the evolution of liverworts. Functional considerations suggest that stomata evolved from pores in the epidermis of plant organs which were at least three cell layers thick and had intercellular gas spaces and a cuticle; an endohydric conducting system would not have been necessary for low-growing rhizophytes, especially in early Palaeozoic CO2-rich atmospheres. The ‘prestomatal state’ (pores) would have permitted higher photosynthetic rates per unit ground area. Functional stomata, and endohydry, permit the evolution of homoiohydry and the loss of vegetative desiccation tolerance and plants > 1 m tall. Stomatal functioning would then have involved maintenance of hydration, and restricting the occurrence of xylem embolism, under relatively desiccating conditions at the expense of limiting carbon acquisition. The time scale of environmental fluctuations over which stomatal responses can maximize carbon gain per unit water loss varies among taxa and life forms.
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Land plant biochemistry.
Philosophical Transactions of the Royal Society B, 2000Co-Authors: John A. RavenAbstract:Biochemical studies have complemented ultrastructural and, subsequently molecular genetic evidence consistent with the Charophyceae being the closest extant algal relatives of the Embryophytes. Among the genes used in such molecular phylogenetic studies is that rbcL) for the large subunit of ribulose bisphosphate carboxylase-oxygenase (RUBISCO). The RUBISCO of the Embryophytes is derived, via the Chlorophyta. from that of the cyanobacteria. This clade of the molecular phylogeny of RUBISCO shows a range of kinetic characteristics, especially of CO2 affinities and of CO2/O2 selectivities. The range of these kinetic values within the bryophytes is no greater than in the rest of the Embryophytes; this has implications for the evolution of the Embryophytes in the high atmospheric CO2 environment of the late Lower Palaeozoic. The differences in biochemistry between charophycean algae and Embryophytes can to some extent be related functionally to the structure and physiology of Embryophytes. Examples of components of Embryophytes, which are qualitatively or quantitatively different from those of charophytes, are the water repellent/water resistant extracellular lipids, the rigid phenolic polymers functional in water-conducting elements and mechanical support in air, and in UV-B absorption, flavonoid phenolics involved in UV-B absorption and in interactions with other organisms, and the greater emphasis on low Mr organic acids. retained in the plant as free acids or salts, or secreted to the rhizosphere. The roles of these components are discussed in relation to the environmental conditions at the time of evolution of the terrestrial Embryophytes. A significant point about Embryophytes is the predominance of nitrogen-free extracellular structural material (a trait shared by most algae) and UV-B screening components, by contrast with analogous components in many other organisms. An important question, which has thus far been incompletely addressed, is the extent to which the absence from bryophytes of the biochemical pathways which produce components found only in tracheophytes is the result of evolutionary loss of these functions.
Dianne Edwards - One of the best experts on this subject based on the ideXlab platform.
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the interrelationships of land plants and the nature of the ancestral Embryophyte
Current Biology, 2018Co-Authors: Paul Kenrick, Dianne Edwards, Charles H. Wellman, Mark N Puttick, Jennifer L Morris, T Williams, Silvia Pressel, Harald SchneiderAbstract:Summary The evolutionary emergence of land plant body plans transformed the planet. However, our understanding of this formative episode is mired in the uncertainty associated with the phylogenetic relationships among bryophytes (hornworts, liverworts, and mosses) and tracheophytes (vascular plants). Here we attempt to clarify this problem by analyzing a large transcriptomic dataset with models that allow for compositional heterogeneity between sites. Zygnematophyceae is resolved as sister to land plants, but we obtain several distinct relationships between bryophytes and tracheophytes. Concatenated sequence analyses that can explicitly accommodate site-specific compositional heterogeneity give more support for a mosses-liverworts clade, "Setaphyta," as the sister to all other land plants, and weak support for hornworts as the sister to all other land plants. Bryophyte monophyly is supported by gene concatenation analyses using models explicitly accommodating lineage-specific compositional heterogeneity and analyses of gene trees. Both maximum-likelihood analyses that compare the fit of each gene tree to proposed species trees and Bayesian supertree estimation based on gene trees support bryophyte monophyly. Of the 15 distinct rooted relationships for Embryophytes, we reject all but three hypotheses, which differ only in the position of hornworts. Our results imply that the ancestral Embryophyte was more complex than has been envisaged based on topologies recognizing liverworts as the sister lineage to all other Embryophytes. This requires many phenotypic character losses and transformations in the liverwort lineage, diminishes inconsistency between phylogeny and the fossil record, and prompts re-evaluation of the phylogenetic affinity of early land plant fossils, the majority of which are considered stem tracheophytes.
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Photosynthesis in Early Land Plants: Adapting to the Terrestrial Environment
Advances in Photosynthesis and Respiration, 2013Co-Authors: John A. Raven, Dianne EdwardsAbstract:The embryophytic land plants evolved from charophycean green algae, one of the three clades of green algae which are important components of the microflora of present-day terrestrial habitats. The earliest Embryophytes are recognised in the fossil record from their characteristic spores, with little evidence as to their vegetative structure. These earliest Embryophytes presumably resemble the extant terrestrial green algae in being desiccation tolerant and poikilohydric. Only the embrophytes subsequently developed the homoiohydry which characterised the organism which today contribute most of the biomass and primary productivity on land, and allowed many of the organisms to become desiccation intolerant in the vegetative phase. Pre-Carboniferous land plant fossils have very few examples of bryophytes other than spores: exceptions are the Middle Devonian Metzgeriothallus and the Upper Devonian Pallaviciniites. Many of the other fossils are recognisable as polysporangiophytes, including vascular plants. Homoiohydry in some of these plants is shown by the occurrence of cuticle and stomata, although there is no fossil evidence bearing on desiccation tolerance/intolerance. In addition to the Embryophytes there are many other fossils, e.g. Pachytheca, Parka, Protosalvinia, Prototaxites and Spongiophyton, which are probably photosynthetic organisms, but are not readily classified: algae, bryophytes and lichens have been suggested, in addition to the possibility that some represent terrestrial fungi. The high atmospheric CO2 concentrations in the early Phanerozoic would have permitted higher rates of photosynthesis than occurs today on the basis of the surface area of the plant exposed to the gas phase because large concentration gradients from the atmosphere to the carboxylase driving diffusive entry of CO2 are possible. Relatively complex morphologies (several layers of photosynthetic structures) and/or anatomy (ventilation within the organisms using gas spaces) are required if the light-harvesting capacity is to be matched by the CO2 assimilation capacity.
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A new group of Early Devonian plants with valvate sporangia containing sculptured permanent dyads
Botanical Journal of the Linnean Society, 2012Co-Authors: Dianne Edwards, J. B. Richardson, Kevin L. DaviesAbstract:As part of a study to explore diversity and disparity in Early Devonian terrestrial vegetation, several hundreds of sporangia with in situ spores have been isolated from a Lochkovian locality in Shropshire. These include a small number (seven) of sporangia showing dehiscence into four valves and containing permanent sculptured dyads, belonging to the Cymbohilates horridus complex and C. cymosus, which are recorded in coeval dispersed spore assemblages. A further, previously described, mesofossil comprises an incomplete sporangium containing C. horridus that terminates a naked isotomously branching stem with stomata. The valvate sporangia are placed in a new genus, Partitatheca, containing four species, P. splendida (type), P. horrida, P. densa and P. cymosa, their names reflecting the names of the dispersed spore species and varieties. Complex ultrastructure in the walls of the dyads is similar to that in earlier dyads in the Dyadospora complex where it provides evidence for a hepatic affinity of the earliest Embryophytes, but the new taxa present a combination of bryophyte and tracheophyte characters and are considered to represent a new Embryophyte lineage. General discussion includes the development of dyads, more particularly their relevance to understanding the diversity in meiotic processes, and the disappearance of dyads from the dispersed spore record prior to the Middle Devonian.
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Lower Devonian plant and spore assemblages from Lower Old Red Sandstone strata of Tredomen Quarry, South Wales
Review of Palaeobotany and Palynology, 2011Co-Authors: Jennifer L Morris, J. B. Richardson, Dianne EdwardsAbstract:Abstract Tredomen Quarry, near Brecon, South Wales, is regarded as a Lower Old Red Sandstone terrestrial lagerstatten and has yielded a palaeobotanical assemblage that illustrates the diversity and possible affinities of early vegetation across the Anglo–Welsh Basin during the lower Lochkovian (Early Devonian). Two boreholes were drilled at the site and subsequent logging resolved the stratigraphic position of the quarry to 64 m above the Bishop's Frome Limestone, thus the lower part of the St. Maughans Formation, a level which few other Anglo–Welsh Basin outcrops expose. A palynological assemblage from the quarry surface is assigned to the lower micrornatus-newportensis Sub-biozone of the lower Lochkovian. The assemblage is diverse, a notable characteristic being ornamented hilate cryptospores of which new species and varieties of Cymbohilates are described ( Cymbohilates horridus var. A, Cymbohilates cymosus var. A–C, Cymbohilates ? sp. A–D). Large rhyniophytes and rhyniophytoids including Cooksonia, Salopella and Tarrantia comprise one component of the palaeobotanical assemblage, typical of southern Britain during the Lochkovian. A diverse group of minute axial plants (mesofossils) constitute a second component, rarely found in other assemblages and considered to be synonymous with the exceptionally well-preserved, charcoalified minute sporangia discovered from a mid-Lochkovian locality. Here they provide for the first time evidence that these minute plants were highly branched and are considered to be stem-group Embryophytes with both tracheophytic and bryophytic characters, hence a separate component of vegetation living alongside the rhyniophytes and rhyniophytoids. Non-Embryophytes form the third component of vegetation and include Nematasketum/Prototaxites and Pachytheca . Minute coalified banded tubes are observed intertwined across bedding planes and are interpreted as hyphae that may have derived from these non-Embryophytes.
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Physiological evolution of lower Embryophytes: Adaptations to the terrestrial environment
The Evolution of Plant Physiology, 2007Co-Authors: John A. Raven, Dianne EdwardsAbstract:Publisher Summary This chapter examines the differences in physiology among Embryophytes and their algal ancestors, with particular emphasis on their water relations. The Embryophytes have very significant variations in water relations and the chapter considers their evolution within the Embryophytes as well as the evolution of Embryophyte water relations from those of their algal ancestors. The chapter also examines the relationship of the likely evolution of Embryophyte water relations to cladistic analyses of Embryophyte phylogeny and to the fossil record. The physiological changes that occurred in the evolution from algal ancestors to the different grades of organization of Embryophytes has been determined from the physiology of extant plants in relation to their phylogeny as determined by cladistic analysis and from the order in which anatomical features appeared in the fossil record. The fossil record of Embryophytes also reveals certain characteristics of organisms that are not found today. The fossil record is not helpful in providing some information such as desiccation tolerance or intolerance, except by applying an empirical correlation from extant plants that no Embryophyte more than 1 meter in height is desiccation tolerant in the vegetative phase. Overall, lines of evidence indicate that the earliest Embryophytes were desiccation tolerant and poikilohydric.
John M Archibald - One of the best experts on this subject based on the ideXlab platform.
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Embryophyte stress signaling evolved in the algal progenitors of land plants
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Jan De Vries, Bruce A Curtis, Sven B Gould, John M ArchibaldAbstract:Streptophytes are unique among photosynthetic eukaryotes in having conquered land. As the ancestors of land plants, streptophyte algae are hypothesized to have possessed exaptations to the environmental stressors encountered during the transition to terrestrial life. Many of these stressors, including high irradiance and drought, are linked to plastid biology. We have investigated global gene expression patterns across all six major streptophyte algal lineages, analyzing a total of around 46,000 genes assembled from a little more than 1.64 billion sequence reads from six organisms under three growth conditions. Our results show that streptophyte algae respond to cold and high light stress via expression of hallmark genes used by land plants (Embryophytes) during stress–response signaling and downstream responses. Among the strongest differentially regulated genes were those associated with plastid biology. We observed that among streptophyte algae, those most closely related to land plants, especially Zygnema , invest the largest fraction of their transcriptional budget in plastid-targeted proteins and possess an array of land plant-type plastid-nucleus communication genes. Streptophyte algae more closely related to land plants also appear most similar to land plants in their capacity to respond to plastid stressors. Support for this notion comes from the detection of a canonical abscisic acid receptor of the PYRABACTIN RESISTANCE (PYR/PYL/RCAR) family in Zygnema , the first found outside the land plant lineage. We conclude that a fine-tuned response toward terrestrial plastid stressors was among the exaptations that allowed streptophytes to colonize the terrestrial habitat on a global scale.