Vascular Plant Lineages Research Articles

The evolution of mechanisms driving the stomatal response to vapor pressure deficit.

Stomatal responses to vapor pressure deficit (VPD) are a principal means by which vascular land plants regulate daytime transpiration. While much work has focused on characterizing and modeling this response, there remains no consensus as to the mechanism that drives it. Explanations range from passive regulation by leaf hydration to biochemical regulation by the phytohormone abscisic acid (ABA). We monitored ABA levels, leaf gas exchange, and water status in a diversity of vascular land plants exposed to a symmetrical, mild transition in VPD. The stomata in basal lineages of vascular plants, including gymnosperms, appeared to respond passively to changes in leaf water status induced by VPD perturbation, with minimal changes in foliar ABA levels and no hysteresis in stomatal action. In contrast, foliar ABA appeared to drive the stomatal response to VPD in our angiosperm samples. Increased foliar ABA level at high VPD in angiosperm species resulted in hysteresis in the recovery of stomatal conductance; this was most pronounced in herbaceous species. Increased levels of ABA in the leaf epidermis were found to originate from sites of synthesis in other parts of the leaf rather than from the guard cells themselves. The transition from a passive regulation to ABA regulation of the stomatal response to VPD in the earliest angiosperms is likely to have had critical implications for the ecological success of this lineage.

Ecophysiology of four co-occurring lycophyte species: an investigation of functional convergence.

Lycophytes are the most early divergent extant lineage of vascular land plants. The group has a broad global distribution ranging from tundra to tropical forests and can make up an important component of temperate northeast US forests. We know very little about the in situ ecophysiology of this group and apparently no study has evaluated if lycophytes conform to functional patterns expected by the leaf economics spectrum hypothesis. To determine factors influencing photosynthetic capacity (Amax), we analysed several physiological traits related to photosynthesis to include stomatal, nutrient, vascular traits, and patterns of biomass distribution in four coexisting temperate lycophyte species: Lycopodium clavatum, Spinulum annotinum, Diphasiastrum digitatum and Dendrolycopodium dendroideum. We found no difference in maximum photosynthetic rates across species, yet wide variation in other traits. We also found that Amax was not related to leaf nitrogen concentration and is more tied to stomatal conductance, suggestive of a fundamentally different sets of constraints on photosynthesis in these lycophyte taxa compared with ferns and seed plants. These findings complement the hydropassive model of stomatal control in lycophytes and may reflect canalization of function in this group. Our data also demonstrate functional ecological similarities: De. dendroideum and D. digitatum are species that have substantial belowground biomass investment and are consistently more similar to each other across multiple traits than either is to the more surficial S. annotinum and L. clavatum. Such differences may partition environments in ways that allow for the close coexistence of these species.

Major evolutionary trends in hydrogen isotope fractionation of vascular plant leaf waxes.

Hydrogen isotopic ratios of terrestrial plant leaf waxes (δD) have been widely used for paleoclimate reconstructions. However, underlying controls for the observed large variations in leaf wax δD values in different terrestrial vascular plants are still poorly understood, hampering quantitative paleoclimate interpretation. Here we report plant leaf wax and source water δD values from 102 plant species grown in a common environment (New York Botanic Garden), chosen to represent all the major lineages of terrestrial vascular plants and multiple origins of common plant growth forms. We found that leaf wax hydrogen isotope fractionation relative to plant source water is best explained by membership in particular lineages, rather than by growth forms as previously suggested. Monocots, and in particular one clade of grasses, display consistently greater hydrogen isotopic fractionation than all other vascular plants, whereas lycopods, representing the earlier-diverging vascular plant lineage, display the smallest fractionation. Data from greenhouse experiments and field samples suggest that the changing leaf wax hydrogen isotopic fractionation in different terrestrial vascular plants may be related to different strategies in allocating photosynthetic substrates for metabolic and biosynthetic functions, and potential leaf water isotopic differences.

Insights into the evolution and diversification of the AT-hook Motif Nuclear Localized gene family in land plants.

BackgroundMembers of the ancient land-plant-specific transcription factor AT-Hook Motif Nuclear Localized (AHL) gene family regulate various biological processes. However, the relationships among the AHL genes, as well as their evolutionary history, still remain unexplored.ResultsWe analyzed over 500 AHL genes from 19 land plant species, ranging from the early diverging Physcomitrella patens and Selaginella to a variety of monocot and dicot flowering plants. We classified the AHL proteins into three types (Type-I/-II/-III) based on the number and composition of their functional domains, the AT-hook motif(s) and PPC domain. We further inferred their phylogenies via Bayesian inference analysis and predicted gene gain/loss events throughout their diversification. Our analyses suggested that the AHL gene family emerged in embryophytes and further evolved into two distinct clades, with Type-I AHLs forming one clade (Clade-A), and the other two types together diversifying in another (Clade-B). The two AHL clades likely diverged before the separation of Physcomitrella patens from the vascular plant lineage. In angiosperms, Clade-A AHLs expanded into 5 subfamilies; while, the ones in Clade-B expanded into 4 subfamilies. Examination of their expression patterns suggests that the AHLs within each clade share similar expression patterns with each other; however, AHLs in one monophyletic clade exhibit distinct expression patterns from the ones in the other clade. Over-expression of a Glycine max AHL PPC domain in Arabidopsis thaliana recapitulates the phenotype observed when over-expressing its Arabidopsis thaliana counterpart. This result suggests that the AHL genes from different land plant species may share conserved functions in regulating plant growth and development. Our study further suggests that such functional conservation may be due to conserved physical interactions among the PPC domains of AHL proteins.ConclusionsOur analyses reveal a possible evolutionary scenario for the AHL gene family in land plants, which will facilitate the design of new studies probing their biological functions. Manipulating the AHL genes has been suggested to have tremendous effects in agriculture through increased seedling establishment, enhanced plant biomass and improved plant immunity. The information gleaned from this study, in turn, has the potential to be utilized to further improve crop production.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0266-7) contains supplementary material, which is available to authorized users.

Between two fern genomes.

Ferns are the only major lineage of vascular plants not represented by a sequenced nuclear genome. This lack of genome sequence information significantly impedes our ability to understand and reconstruct genome evolution not only in ferns, but across all land plants. Azolla and Ceratopteris are ideal and complementary candidates to be the first ferns to have their nuclear genomes sequenced. They differ dramatically in genome size, life history, and habit, and thus represent the immense diversity of extant ferns. Together, this pair of genomes will facilitate myriad large-scale comparative analyses across ferns and all land plants. Here we review the unique biological characteristics of ferns and describe a number of outstanding questions in plant biology that will benefit from the addition of ferns to the set of taxa with sequenced nuclear genomes. We explain why the fern clade is pivotal for understanding genome evolution across land plants, and we provide a rationale for how knowledge of fern genomes will enable progress in research beyond the ferns themselves.

Macroecological and macroevolutionary patterns of leaf herbivory across vascular plants.

The consumption of plants by animals underlies important evolutionary and ecological processes in nature. Arthropod herbivory evolved approximately 415 Ma and the ensuing coevolution between plants and herbivores is credited with generating much of the macroscopic diversity on the Earth. In contemporary ecosystems, herbivory provides the major conduit of energy from primary producers to consumers. Here, we show that when averaged across all major lineages of vascular plants, herbivores consume 5.3% of the leaf tissue produced annually by plants, whereas previous estimates are up to 3.8× higher. This result suggests that for many plant species, leaf herbivory may play a smaller role in energy and nutrient flow than currently thought. Comparative analyses of a diverse global sample of 1058 species across 2085 populations reveal that models of stabilizing selection best describe rates of leaf consumption, and that rates vary substantially within and among major plant lineages. A key determinant of this variation is plant growth form, where woody plant species experience 64% higher leaf herbivory than non-woody plants. Higher leaf herbivory in woody species supports a key prediction of the plant apparency theory. Our study provides insight into how a long history of coevolution has shaped the ecological and evolutionary relationships between plants and herbivores.

Light‐dependent reversible phosphorylation of the minor photosystem II antenna Lhcb6 (CP24) occurs in lycophytes

Evolution of vascular plants required compromise between photosynthesis and photodamage. We analyzed representative species from two divergent lineages of vascular plants, lycophytes and euphyllophytes, with respect to the response of their photosynthesis and light-harvesting properties to increasing light intensity. In the two analyzed lycophytes, Selaginella martensii and Lycopodium squarrosum, the medium phase of non-photochemical quenching relaxation increased under high light compared to euphyllophytes. This was thought to be associated with the occurrence of a further thylakoid phosphoprotein in both lycophytes, in addition to D2, CP43 and Lhcb1-2. This protein, which showed light intensity-dependent reversible phosphorylation, was identified in S.martensii as Lhcb6, a minor LHCII antenna subunit of PSII. Lhcb6 is known to have evolved in the context of land colonization. In S.martensii, Lhcb6 was detected as a component of the free LHCII assemblies, but also associated with PSI. Most of the light-induced changes affected the amount and phosphorylation of the LHCII assemblies, which possibly mediate PSI-PSII connectivity. We propose that Lhcb6 is involved in light energy management in lycophytes, participating in energy balance between PSI and PSII through a unique reversible phosphorylation, not yet observed in other land plants.

The New Phytologist Tansley Medals 2013

The New Phytologist Tansley Medal is awarded to scientists who have made outstanding contributions to plant science within 5 yr of receiving their PhD (Woodward & Hetherington, 2010, 2011; Dolan, 2012, 2013). In 2013 medals were awarded to Jing-Ke Weng, formerly of the Salk Institute, La Jolla (CA, USA), and now based at the Whitehead Institute for Biomedical Research and Massachusetts Institute of Technology (MA, USA), and Li-Qing Chen from the Carnegie Institution, Stanford (CA, USA) (see Box 1). Jing-Ke Weng is a plant biochemist with extensive experience in genomics and metabolomics and has made major contributions to our understanding of the evolution of metabolic pathways. Jing-Ke completed a PhD with Clint Chapple in 2009 at Purdue University (IN, USA) and discovered how the metabolic network leading to the formation of a-pyrone synthesis was assembled during evolution. His time in Indiana was very productive with a series of high impact papers on metabolic pathways in a variety of organisms including Selaginella moellendorffii and Arabidopsis thaliana. Jing-Ke's minireview entitled ‘The evolutionary paths towards complexity: a metabolic perspective ’ is published in this issue of New Phytologist (Weng, pp. 1141–1149). Li-Qing Chen has a background in forest genetics and nutrient acquisition. Li-Qing has published high profile papers outlining important breakthroughs at each stage in her career. She discovered novel regulators of the AKT1 K+ transporter in A. thaliana during her PhD research with Wei-Hua Wu at China Agricultural University in Beijing. She moved to Wolf Frommer's laboratory (in the Carnegie Institution, Stanford) in 2007 and discovered a role for SWEET proteins in phloem loading. Her minireview entitled ‘SWEET sugar transporters for phloem transport and pathogen nutrition’ is published in this issue of New Phytologist (Chen, pp. 1150–1155). There were two excellent runners up. Elizabeth Wolkovich, from the University of British Columbia (BC, Canada), whose minireview ‘Progress towards an interdisciplinary science of plant phenology: building predictions across space, time and species diversity ’ is published in this issue (Wolkovich et al., pp. 1156–1162). Jacquelyn Gill from the University of Wisconsin, Madison (WI, USA), published a minireview entitled ‘Ecological impacts of the Later Quaternary megaherbivore extinctions’ (Gill, pp. 1163–1169). Congratulations to all our finalists on their achievements. The New Phytologist will keep a watchful eye on their burgeoning careers. Jing-Ke undertook PhD research with Dr Clint Chapple at Purdue University on the evolution of phenylpropanoid metabolism in land plants, and in his graduate work Jing-Ke resolved the molecular mechanisms underlying the independent occurrences of syringyl lignin in the two major lineages of vascular plants, lycophytes and angiosperms, which diverged from each other > 400 million yr ago. He also discovered a new class of secondary metabolites, arabidopyrones, and further defined the biosynthesis pathway and evolutionary trajectory underpinning their emergence in Arabidopsis. Jing-Ke was a Pioneer postdoctoral fellow at the Salk Institute under the mentorship of Dr Joseph Noel, where he studied the structure–function relationships underpinning the evolution of a number of specialized metabolic enzyme families in plants, including type III polyketide synthases and BAHD acyltransferases. He joined the faculty of the Whitehead Institute and the Massachusetts Institute of Technology in 2013. For more information on Jing-Ke, visit http://wi.mit.edu/people/faculty/weng or contact him directly at wengj@wi.mit.edu. Li-Qing completed her PhD at China Agricultural University in Beijing and during this period Li-Qing, together with her colleagues, discovered the key CBL–CIPK–AKT1 regulatory pathway when plants were under low potassium stress. Li-Qing has worked in Dr Wolf Frommer's laboratory at the Carnegie Institution, Stanford since 2007, and after taking over a project initiated by an undergraduate student she made significant progress by characterizing a novel class of sugar transporters, SWEETs, which are important for many physiological processes and for pathogen nutritional gain. One year after the characterization of SWEET, Li-Qing, together with another graduate student, made a breakthrough research finding which identified SWEETs as a key player during the sucrose phloem loading process. For more information on Li-Qing, visit https://dpb.carnegiescience.edu/labs/frommer-lab/people or contact her at lchen2@stanford.edu. Jing-Ke and Li-Qing will each receive a £2000 prize in association with the Tansley Medal award http://www.newphytologist.org/tansleymedal.htm

Interannual variation and host affiliations of endophytic fungi associated with ferns at La Selva, Costa Rica

Ferns are an ancient and diverse lineage of vascular plants that differ morphologically, chemically and in growth habits from the angiosperms with which they co-occur. We used a culture-based approach coupled with phylogenetic analyses to characterize the incidence, diversity and composition of fungal endophyte assemblages in ferns, with a focus on healthy aboveground tissues of seven species of eupolypods at La Selva, Costa Rica. Endophytes were isolated from every individual plant and were similarly abundant and diverse in frond blades and stalks, in different vegetation types, in epiphytic vs. terrestrial species, and between sampling years. However, abundance, diversity and community structure differed significantly among fern species, and composition differed markedly between sampling years. Phylogenetic classification using separate and combined datasets revealed that as for many Neotropical angiosperms, the majority (95%) of endophyte taxa were Ascomycota, with particular dominance by Sordariomycetes, Eurotiomycetes and Dothideomycetes. However, our data suggest higher phylogenetic richness and stronger host affinities in fern associated endophytes relative to those studied in angiosperms thus far.

Revision of Cyrtandra (Gesneriaceae) in the Marquesas Islands

During the preparation of the Vascular Flora of the Marquesas Islands three new species of Cyrtandra (Gesneriaceae) have come to light and are described herein: C. uapouensis W. L. Wagner & Lorence, C. uahukaensis W. L. Wagner & Lorence, and C. kenwoodii W. L. Wagner & A. J. Wagner. Amended descriptions of the eight previously described Marquesan species are also provided as well as a key to the species. With the description of these the new species Cyrtandra in the Marquesas Islands consists of 11 species, six of which have been included in recent molecular phylogenetic studies of Pacific Cyrtandra, and appear to have arisen from one original introduction. If the other five species are members of this Marquesas clade then Cyrtandra would represent the largest lineage of Marquesas vascular plants. Psychotria is largest genus in the Marquesas Islands with 13 species, but is thought to consist of three separate lineages.

Morphological and molecular analyses of fungal endophytes of achlorophyllous gametophytes ofDiphasiastrum alpinum(Lycopodiaceae)

To understand the early evolution of mycorrhizal symbioses, it is important to know the fungal partners of gametophytes and sporophytes for basal lineages of vascular plants. Subterranean mycotrophic gametophytes of the clubmoss Diphasiastrum alpinum found at three localities gave an opportunity to study their morphology and anatomy and to identify and describe their hitherto unknown fungal endophytes. In addition, sporophytes were screened for fungal partners. Gametophytes with attached young sporophytes were excavated, and their anatomy and their associated fungi were studied by light microscopy. DNA was isolated and amplified with both universal and group-specific fungal primers for the ITS region, the large subunit and small subunit of the nuclear rDNA, respectively, to identify the fungal partner. Gametophytes were uniformly colonized by a fungus with septate hyphae forming coils and vesicles. Its morphology resembles that of the sebacinoid genus Piriformospora. Both ITS and LSU sequences were identified as Sebacinales group B, a basal clade of the Agaricomycetes (Basidiomycota). This fungus was detected in 11 gametophytes from two localities and in rootlets of adjacent Calluna vulgaris (Ericaceae) plants, but was absent in roots of sporophytes. In addition, several ascomycetes and glomeromycetes were found by DNA sequencing. Our study suggests a fungus belonging to Sebacinales group B as the main fungal host of the D. alpinum gametophytes. However, Sebacinales group B fungi occur as well in adjacent Ericaceae plants; therefore, we assume the mycoheterotrophic gametophyte to be epiparasitic on Ericaceae, which would explain the steady association of these plants.

Plant mitochondrial genome peculiarities evolving in the earliest vascular plant lineages

AbstractIn plants, the mitochondrial DNA has evolved in peculiar ways. Simple circular mitochondrial genomes found in most other eukaryotic lineages have expanded tremendously in size. Mitochondrial DNAs in some flowering plants may in fact be larger than genomes of free‐living bacteria. Introns, retrotransposons, pseudogene fragments, and promiscuous DNA copied from the chloroplast or nuclear genome contribute to the size expansion but most intergenic DNA remains unaccounted for so far. Additionally, frequent recombination results in heterogeneous pools of coexisting, subgenomic mtDNA molecules in angiosperms. In contrast, the mitochondrial DNAs of bryophytes, the extant representatives of very early splits in plant phylogeny, are more conservative in structural evolution and seem to be devoid of active recombination. However, whereas mitochondrial introns are highly conserved among seed plants (spermatophytes), not a single one of more than 80 different introns in bryophyte mtDNAs is conserved among the three divisions, liverworts, mosses, and hornworts. Lycophytes are now unequivocally identified as living representatives of the earliest vascular plant branch in a crucial phylogenetic position between bryophytes and later diversifying tracheophytes including spermatophytes. Very recently, mtDNAs have become available for the three orders of extant lycophytes—Isoetales, Selaginellales, and Lycopodiales. As I will discuss here, the lycophyte mtDNAs not only show a surprising diversity of features but also previously unseen novelties of plant mitochondrial DNA evolution. The transition from a gametophyte‐dominated bryophyte lifestyle to a sporophyte‐dominated vascular plant lifestyle apparently gave rise to several peculiar independent changes in plant chondrome evolution.

The association of a La module with the PABP-interacting motif PAM2 is a recurrent evolutionary process that led to the neofunctionalization of La-related proteins

La-related proteins (LARPs) are largely uncharacterized factors, well conserved throughout evolution. Recent reports on the function of human LARP4 and LARP6 suggest that these proteins fulfill key functions in mRNA metabolism and/or translation. We report here a detailed evolutionary history of the LARP4 and 6 families in eukaryotes. Genes coding for LARP4 and 6 were duplicated in the common ancestor of the vertebrate lineage, but one LARP6 gene was subsequently lost in the common ancestor of the eutherian lineage. The LARP6 gene was also independently duplicated several times in the vascular plant lineage. We observed that vertebrate LARP4 and plant LARP6 duplication events were correlated with the acquisition of a PABP-interacting motif 2 (PAM2) and with a significant reorganization of their RNA-binding modules. Using isothermal titration calorimetry (ITC) and immunoprecipitation methods, we show that the two plant PAM2-containing LARP6s (LARP6b and c) can, indeed, interact with the major plant poly(A)-binding protein (PAB2), while the third plant LARP6 (LARP6a) is unable to do so. We also analyzed the RNA-binding properties and the subcellular localizations of the two types of plant LARP6 proteins and found that they display nonredundant characteristics. As a whole, our results support a model in which the acquisition by LARP4 and LARP6 of a PAM2 allowed their targeting to mRNA 3' UTRs and led to their neofunctionalization.

Comparative metabolic profiling between desiccation‐sensitive and desiccation‐tolerant species of Selaginella reveals insights into the resurrection trait

Spike mosses (Selaginellaceae) represent an ancient lineage of vascular plants in which some species have evolved desiccation tolerance (DT). A sister-group contrast to reveal the metabolic basis of DT was conducted between a desiccation-tolerant species, Selaginella lepidophylla, and a desiccation-sensitive species, Selaginella moellendorffii, at 100% relative water content (RWC) and 50% RWC using non-biased, global metabolomics profiling technology, based on GC/MS and UHLC/MS/MS(2) platforms. A total of 301 metabolites, including 170 named (56.5%) and 131 (43.5%) unnamed compounds, were characterized across both species. S. lepidophylla retained significantly higher abundances of sucrose, mono- and polysaccharides, and sugar alcohols than did S.moellendorffii. Aromatic amino acids, the well-known osmoprotectant betaine and flavonoids were also more abundant in S.lepidophylla. Notably, levels of γ-glutamyl amino acid, linked with glutathione metabolism in the detoxification of reactive oxygen species, and with possible nitrogen remobilization following rehydration, were markedly higher in S.lepidophylla. Markers for lipoxygenase activity were also greater in S.lepidophylla, especially at 50% RWC. S.moellendorffii contained more than twice the number of unnamed compounds, with only a slightly greater abundance than in S.lepidophylla. In contrast, S.lepidophylla contained 14 unnamed compounds of fivefold or greater abundance than in S.moellendorffii, suggesting that these compounds might play critical roles in DT. Overall, S.lepidophylla appears poised to tolerate desiccation in a constitutive manner using a wide range of metabolites with some inducible components, whereas S.moellendorffii mounts only limited metabolic responses to dehydration stress.

Molecular Determinants that Convert Hormone Sensitive Lipase into Gibberellin Receptor

Gibberellins (GAs) are tetracyclic, diterpenoid plant hormones, essential for many developmental processes in higher plants. Plants perceive GA through a nuclear-localized GA receptor, GA INSENSITIVE DWARF1 (GID1). From sequence similarity, it is suggested that GID1 evolved from a hormone-sensitive lipase (HSL), and recent x-ray crystallography of the GA-GID1 complex has given insights into how GID1 recognizes GA. Analyses of the GA signaling pathway in several plant species further suggest that the GID1-mediated GA signaling pathway emerged in the vascular plant lineage and since then regulation of GA recognition specificity seems to have been fine tuned to strictly regulate the on-off GA signal.

Amino Acid Transporter Inventory of the Selaginella Genome

Amino acids play fundamental roles in a multitude of functions including protein synthesis, hormone metabolism, nerve transmission, cell growth, production of metabolic energy, nucleobase synthesis, nitrogen metabolism, and urea biosynthesis. Selaginella as a member of the lycophytes is part of an ancient lineage of vascular plants that had arisen ∼400 million years ago. In angiosperms, which have attracted most of the attention for nutrient transport so far, we have been able to identify many of the key transporters for nitrogen. Their role is not always fully clear, thus an analysis of Selaginella as a representative of an ancient vascular plant may help shed light on the evolution and function of these diverse transporters. Here we annotated and analyzed the genes encoding putative transporters involved in cellular uptake of amino acids present in the Selaginella genome.

Plant Genomics: Homoplasy Heaven in a Lycophyte Genome

The recent genomic sequencing of Selaginella, a member of the lycophyte lineage of vascular plants, opens up all kinds of new opportunities to examine the patterns of evolutionary innovation and the creation of the basic bauplan of plants.

Phylogenetic analysis of GRAS proteins from moss, lycophyte and vascular plant lineages reveals that GRAS genes arose and underwent substantial diversification in the ancestral lineage common to bryophytes and vascular plants

GRAS genes are a large family of streptophyte specific transcription factors that function in a diverse set of physiological and developmental processes. GRAS proteins of the HAIRY MERISTEM (HAM) sub-family are required for maintenance of shoot and root indeterminacy. The transcriptional targets of HAM proteins and the signaling inputs regulating HAM activity are completely unknown. Understanding the relationship of HAM proteins to other members of the GRAS family may inform hypotheses relating to cellular level HAM functions. I here report a phylogenetic analysis of GRAS proteins employing the complete set of known and probable GRAS proteins from the sequenced genomes of the flowering plants Arabidopsis and Rice, the lycophyte Selaginella moellendorffii, and the bryophyte Physcomitrella patens. HAM proteins are most closely related to DELLA proteins, key components of gibberellin perception. However, GRAS proteins diversified into a minimum of twelve discreet monophyletic lineages, including the HAM and DELLA subfamilies, prior to divergence of the moss and flowering plant lineages. Substantial diversification of GRAS proteins at so early a point in land plant evolution suggests that relative relatedness sequence homology among GRAS proteins sub-families may not substantially reflect shared protein function.

Land Plants Acquired Active Stomatal Control Early in Their Evolutionary History

Stomata are pores that regulate plant gas exchange [1]. They evolved more than 400 million years ago [2, 3], but the origin of their active physiological responses to endogenous and environmental cues is unclear [2-6]. Recent research suggests that the stomata of lycophytes and ferns lack pore closure responses to abscisic acid (ABA) and CO(2). This evidence led to the hypothesis that a fundamental transition from passive to active control of plant water balance occurred after the divergence of ferns 360 million years ago [7, 8]. Here we show that stomatal responses of the lycophyte Selaginella [9] to ABA and CO(2) are directly comparable to those of the flowering plant Arabidopsis [10]. Furthermore, we show that the underlying intracellular signaling pathways responsible for stomatal aperture control are similar in both basal and modern vascular plant lineages. Our evidence challenges the hypothesis that acquisition of active stomatal control of plant carbon and water balance represents a critical turning point in land plant evolution [7, 8]. Instead, we suggest that the critical evolutionary development is represented by the innovation of stomata themselves and that physiologically active stomatal control originated at least as far back as the emergence of the lycophytes (circa 420 million years ago) [11].

Plant fossil record and survival analyses

Cascales-Minana, B. & Cleal, C.J. 2011: Plant fossil record and survival analyses. Lethaia, Vol. 45, pp. 71–82. Survival analysis is a classic palaeobiological method widely used on the animal fossil record. This study reports the first application of survivorship analyses on the plant fossil record from a global viewpoint and provides a new comparative approach of this methodology. The results reveal three important plant extinction events in the history of plant life at a global scale. The results also clearly suggest that the origination events are more intensive than extinction processes and that the origination moment of several lineages of vascular plants is an important factor that conditions their longevity. This study supports the general idea that vascular plants tended to be less affected by the environmental changes that caused mass extinction in other groups of organisms. □Extinction events, fossil record, survival patterns, taxonomic survivorship curves, vascular plants.