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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, Gane Ka-shu Wong, Jean Michel Doan, Brandon A. Wustman, Eric J. Carpenter, Yong Zhang, Li Chen, 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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RESEARCH ARTICLE Open Access Origin of land plants: Do conjugating green algae hold the key?
2013Co-Authors: Sabina Wodniok, Michael Melkonian, Henner Brinkmann, Gernot Glöckner, Andrew J. Heidel, Burkhard BeckerAbstract:Background: 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. Results: 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. Conclusions: Our analyses support the notion that the Charales are not the closest living relatives o
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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, Michael Melkonian, Henner Brinkmann, Gernot Glöckner, Andrew J. Heidel, Herve Philippe, 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:BACKGROUND 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. RECENT PROGRESS 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. CONCLUSIONS 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.
Linda E. Graham - One of the best experts on this subject based on the ideXlab platform.
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Phylogenetic Position of the Green Flagellate Mesostigma viride Based on α‐Tubulin and β‐Tubulin Gene Sequences
International Journal of Plant Sciences, 2006Co-Authors: Lee W. Wilcox, Marvin W. Fawley, Linda E. GrahamAbstract:The green alga Mesostigma viride has attracted considerable recent attention as a model system useful for understanding the evolutionary origin of the Viridiplantae (all green algae plus Embryophytes) or the Streptophyta (charophycean algae plus Embryophytes). Mesostigma’s utility for such studies depends on its phylogenetic position, which has been controversial. Phylogenetic analyses based on organellar genes have given conflicting results; some support a hypothesis that Mesostigma represents the first branch of the Viridiplantae, whereas others support an alternative hypothesis that it occupies a basal position within Streptophyta. Nuclear‐encoded actin and small subunit ribosomal gene sequences also mark Mesostigma as a basal lineage in Streptophyta. We tested these two alternative hypotheses by analyses of nuclear‐encoded α‐ and β‐tubulin sequences. We obtained new α‐ and β‐tubulin gene sequences from M. viride as well as from the charophycean Coleochaete scutata and the green flagellates Pterosperma...
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The origin of alternation of generations in land plants: a focus on matrotrophy and hexose transport
Philosophical Transactions of the Royal Society B, 2000Co-Authors: Linda E. Graham, Lee W. WilcoxAbstract:A life history involving alternation of two developmentally associated, multicellular generations (sporophyte and gametophyte) is an autapomorphy of Embryophytes (bryophytesphytes + vascular plants). Microfossil data indicate that Mid Late Ordovician land plants possessed such a life cycle, and that the origin of alternation of generations preceded this date. Molecular phylogenetic data unambiguously relate charophycean green algae to the ancestry of monophyletic Embryophytes, and identify bryophytes as early-divergent land plants. Comparison of reproduction in charophyceans and bryophytes suggests that the following stages occurred during evolutionary origin of embryophytic alternation of generations: (i) origin of oogamy; (ii) retention of eggs and zygotes on the parental thallus; (iii) origin of matrotrophy (regulated transfer of nutritional and morphogenetic solutes from parental cells to the next generation); (iv) origin of a multicellular sporophyte generation; and (v) origin of non-flagellate, walled spores. Oogamy, egg/zygote retention and matrotrophy characterize at least some modern charophvceans, and are postulated to represent pre-adaptative features inherited by Embryophytes from ancestral charophyceans. Matrotrophy is hypothesized to have preceded origin of the multicellular sporophytes of' plants, and to represent a critical innovation. Molecular approaches to the study of the origins of matrotrophy include assessment of hexose transporter genes and protein family members and their expression patterns. The occurrence in modern charophyceans and bryophytes of chemically resistant tissues that exhibit distinctive morphology correlated with matrotrophy suggests that Early-Mid Ordovician or older microfossils relevant to the origin of land plant alternation of generations may be found.
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Green algae to land plants: An evolutionary transition
Journal of Plant Research, 1996Co-Authors: Linda E. GrahamAbstract:Studies focused upon the evolutionary transition from ancestral green algae to the earliest land plants are important from a range of ecological, molecular and evolutionary perspectives. A substantial suite of ultrastructural, biochemical and molecular data supports the concept that land plants (Embryophytes) are monophyletically derived from an ancestral charophycean alga. However, the details of phylogenetic branching patterns linking extant charophytes and seedless Embryophytes are currently unclear. Moreover, the fossil record has so far been mute regarding the algae-land plant transition. Nevertheless, an accurate reflection of major evolutionary events in the history of the earliest land plants can be obtained by comparative paleontological-neontological studies, and comparative molecular, cellular and developmental investigations of extant charophytes and bryophytes. This review focuses upon research progress toward understanding three clade-specific adaptations that were important in the successful colonization of land by plants: the histogenetic apical meristem, the matrotrophic embryo, and decay-resistant cell wall polymers.
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Subcellular structures of relevance to the origin of land plants (Embryophytes) from green algae
Critical Reviews in Plant Sciences, 1991Co-Authors: Linda E. Graham, Yasuko Kaneko, Karen S RenzagliaAbstract:Abstract During the past 2 decades, a substantial body of structural, biochemical, and molecular evidence has been amassed in support of the hypothesis that charophycean green algae are the closest extant protist relatives of the land plants (Embryophytes). Charophycean algae include the filamentous and unicellular Zygnematales, represented by the familiar Spirogyra and desmids; the relatively large and complex Charales, such as Chara; the less conspicuous, but well‐studied Coleochaete; and several other less well‐known taxa. Ultrastructural studies of these green algae have revealed a variety of subcellular structures which are shared with land plants, and which are absent from most other algae. This article describes the phylogenetic importance of the cytoskeleton (including mitotic and meiotic division apparatus), peroxisomes, cell wall features, and organelles found in specialized cells such as spermatozoids, by comparison with correlative subcellular structures in Embryophytes.
John A. Raven - One of the best experts on this subject based on the ideXlab platform.
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Protein assemblages and tight curves in the plasma membranes of photosynthetic eukaryotes.
Journal of plant physiology, 2020Co-Authors: John A. Raven, Mary J. BeilbyAbstract:Abstract Protein assemblages in the plasma membrane of photosynthetic organisms include the polar occurrence of PIN proteins permitting polar auxin transport in Embryophytes and Charales, and the H+ ATPase in acid zones of Charales cells. Production of small radius of curvature membrane areas in transfer cells and charasomes is incompletely understood.
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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.
James R. Manhart - One of the best experts on this subject based on the ideXlab platform.
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The Transition From Algae to Embryophytes: Chloroplast Phylogenomic Evidence (II)
Journal of Phycology, 2002Co-Authors: James R. ManhartAbstract:The transition of plant life from aquatic algae to land plants was one of the major events in the history of life. However, in hypothesizing the evolutionary path of the transition, limited shared phenotypic characters in aquatic algae and land plants (Embryophytes) have been a major hinderance. Chloroplast genomes contain characters useful in tracing evolutionary histories. Embryophyte chloroplast genomes are distinguished from algal cpDNAs by the presence of over 20 group II introns and three ribosomal protein operons (rpl23, clpP and 3Œrps12 operons). These phylogenomic features indicate a phylogenetic relationship of charophytes and Embryophytes. In addition to these operons and introns, the evolution of rRNA and psbB operon evolution of streptophyte lineages will be incorporated with major biological phenotypic features to produce a phylogenetic tree. Basal Embryophytes, the antithetic hypothesis, monophyly of Embryophytes, and paraphyly of charophytes will be discussed. Strepotophytes are classified into three major groups (basal streptophytes, mid-divergent streptophytes and late divergent charophytes-Embryophytes).
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Four Embryophyte Introns and psbB Operon Indicate Chlorokybus as a Basal Streptophyte Lineage
Algae, 2002Co-Authors: Lee Jung-ho, James R. ManhartAbstract:The transition of plant life from aquatic algae to land to land plants was one of the major events in the history of life. However, in hypothesizing the exact evolutionary path of the transition, limited shared phenotypic characters in aquatic algae and land plants (Embryophytes) have been a major hinderance. Chloroplast genomes contain characters useful in tracing evolutionary histories. Embryophyte chloroplast genomes are distinguished from algal cpDNAs by having over 20 group Ⅱ introns, some of which were gained during the transition from algae to Embryophytes (Manhart and Palmer 1990; Lew and Manhart 1993;Lee and Manhart 2002). Here we examine a gene cluster that, in land plants, contains psbB, psbT, psbH, petB and petD with introns found in petB and petD (petB.i and petD.i). In addition the presence/absence of introns in trnA and trnI (trnA.i and trnI.i) were determined in all five major lineages of charophytes. We found that the psbB gene cluster occurs in most surveyed charophytes and Embryophytes except Spirogyra (Zygnematales) which lacks it due to intra-genomic rearrangement. All four introns are absent in Chlorokybus but present in some or all of the other four charophyte lineages (Klebsormidiales, Zygnematales, Coleochaetales, and Charales). In addition, Chlorokybus is distinguished from other charophytes and Embryophytes by having an unusually long spacer (over 2 kb) between psbH-petB. The results indicate that Chlorokybus diverged before the intron gains but after psbB gene cluster formation, placing the other charophyte lineages closer to Embryophytes.
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The Chloroplast rpl23 Gene Cluster of Spirogyra maxima (Charophyceae) Shares Many Similarities with the Angiosperm rpl23 Operon
Algae, 2002Co-Authors: James R. ManhartAbstract:A phylogenetic affinity between charophytes and Embryophytes (land plants) has been explained by a few chloroplast genomic characters including gene and intron (Manhart and Palmer 1990; Baldauf et al. 1990; Lew and Manhart 1993). Here we show that a charophyte, Spirogyra maxima, has the largest operon of angiosperm chloroplast genomes, rpl23 operon (trnⅠ-rpl23-rpl2-rps19-rpl22-rps3-rpl16-rpl14-rps8-infA-rpl36-rps11-rpoA) containing both embryophyte introns, rpl16.i and rpl2.i. The rpl23 gene cluster of Spirogyra contains a distinct eubacterial promoter sequence upstream of rpl23, which is the first gene of the green algal rpl23 gene cluster. This sequence is completely absent in angiosperms but is present in non-flowering plants. The results imply that, in the rpl23 gene cluster, early charophytes had at least two promoters, one upstream of trnⅠ and and another upstream of rpl23, which partially or completely lost its function in land plants. A comparison of gene clusters of prokaryotes, algal chloroplast DNAs and land plant cpDNAs indicated a loss of numerous genes in chlorophyll a+b eukaryotes. A phylogenetic analysis using presence/absence of genes and introns as characters produced trees with a strongly supported clade containing chlorophyll a+b eukaryotes. Spirogyra and Embryophytes formed a clade characterized by the loss of rpl5 and rps9 and the gain of trnⅠ (CAU) and introns in rpl2 and rpl16. The analyses support the hypothesis that the rpl23 gene cluster and the rpl2 and rpl16 introns of land plants originated from a common ancestor of Spirogyra and land plants.
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, Jean Keller, Birger Marin, Xiuli Li, Yuan Fu, Yan Xu, Tian Wu, 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:BACKGROUND 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. RECENT PROGRESS 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. CONCLUSIONS 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.