Life on Earth as we know it would not be possible without the evolution of plants, and without the transition of plants to live on land. Land plants (also known as embryophytes) are a monophyletic ...lineage embedded within the green algae. Green algae as a whole are among the oldest eukaryotic lineages documented in the fossil record, and are well over a billion years old, while land plants are about 450–500 million years old. Much of green algal diversification took place before the origin of land plants, and the land plants are unambiguously members of a strictly freshwater lineage, the charophyte green algae. Contrary to single-gene and morphological analyses, genome-scale phylogenetic analyses indicate the sister taxon of land plants to be the Zygnematophyceae, a group of mostly unbranched filamentous or single-celled organisms. Indeed, several charophyte green algae have historically been used as model systems for certain problems, but often without a recognition of the specific phylogenetic relationships among land plants and (other) charophyte green algae. Insight into the phylogenetic and genomic properties of charophyte green algae opens up new opportunities to study key properties of land plants in closely related model. This review will outline the transition from single-celled algae to modern-day land plants, and will highlight the bright promise studying the charophyte green algae holds for better understanding plant evolution.
Delwiche and Cooper outline the transition from single-celled algae to modern-day land plants, and highlight the bright promise studying the charophyte green algae holds for better understanding plant evolution.
The emergence and radiation of multicellular land plants was driven by crucial innovations to their body plans 1. The directional transport of the phytohormone auxin represents a key, plant-specific ...mechanism for polarization and patterning in complex seed plants 2–5. Here, we show that already in the early diverging land plant lineage, as exemplified by the moss Physcomitrella patens, auxin transport by PIN transporters is operational and diversified into ER-localized and plasma membrane-localized PIN proteins. Gain-of-function and loss-of-function analyses revealed that PIN-dependent intercellular auxin transport in Physcomitrella mediates crucial developmental transitions in tip-growing filaments and waves of polarization and differentiation in leaf-like structures. Plasma membrane PIN proteins localize in a polar manner to the tips of moss filaments, revealing an unexpected relation between polarization mechanisms in moss tip-growing cells and multicellular tissues of seed plants. Our results trace the origins of polarization and auxin-mediated patterning mechanisms and highlight the crucial role of polarized auxin transport during the evolution of multicellular land plants.
•PIN-mediated auxin transport is operational in the moss Physcomitrella patens•Plasma membrane PIN proteins localize in a polar manner in gametophytic tissue•Intercellular auxin transport mediates key developmental decisions in Physcomitrella
Viaene et al. show in the moss Physcomitrella patens that PIN-mediated auxin transport mediates crucial developmental transitions in tip-growing filaments and waves of polarization and differentiation in leaf-like structures.
•Plant phylogeny is incompletely resolved.•Molecular evolution often violates phylogenetic model assumptions.•Improved phylogenetic models are being developed.•Data are quickly becoming unlimited for ...phylogenetic analysis.
Phylogenetic analysis is an increasingly common and valuable component of plant science. Knowledge of the phylogenetic relationships between plant groups is a prerequisite for understanding the origin and evolution of important plant features, and phylogenetic analysis of individual genes and gene families provides fundamental insights into how those genes and their functions evolved. However, despite an active research community exploring and improving phylogenetic methods, the analytical methods commonly used, and the phylogenetic results they produce, are accorded far more confidence than they warrant. In this opinion article, I emphasise that important parts of the green plant phylogeny are inconsistently resolved and I argue that the lack of consistency arises due to inadequate modelling of changes in the substitution process.
Developing a structurally complex phenotype requires a complex regulatory network. A new study shows how gene duplication provides a potential source of antagonistic interactions, an important ...component of gene regulatory networks.
Developing a structurally complex phenotype requires a complex regulatory network. A new study shows how gene duplication provides a potential source of antagonistic interactions, an important component of gene regulatory networks.
Few facts in biology are more certain than offspring inheriting genetic material from their parents, but not all genes are acquired this way. A new report documents the horizontal transfer of a ...potentially adaptive gene between distantly related plants.
The Australian National Species List (AuNSL) is a unified, nationally accepted, taxonomy for the native and naturalised biota of Australia. It is derived from a set of taxon-focussed resources ...including the Australian Plant Name Index and Australian Plant Census, the Australian Faunal Directory, and similar lists of fungi, lichens and bryophytes. These resources share a common infrastructure, contribute to the single national taxonomy (AuNSL), but retain their independent curation practices and online presentation. The AuNSL is now the core national infrastructure providing names and taxonomy for significant biodiversity data infrastructures including the Atlas of Living Australia, the Terrestrial Ecosystem Research Network, the Biodiversity Data Repository, and the Species Profile and Threats Database.
As the go-to resource for names and taxonomy for Australia’s unique biodiversity, the AuNSL must be constantly updated to reflect taxonomic and nomenclatural change. For some taxonomic groups, the AuNSL is substantially complete, and the incorporation of new taxa and other novelties occurs with little time lag. For other taxonomic groups the data are patchy and updates sporadic. Like similar projects, the AuNSL would benefit from improvements to taxonomic data publishing and sharing. Such improvements have the potential to enable automated, real-time ingestion for new taxonomic and nomenclatural data, allowing curator time to be re-directed to backfilling the historical data from a dispersed and complex literature. Ideally, the AuNSL will be able to benefit from advances in automated approaches to processing the historical data, including via the sharing of standardised representations of such data.
Here we outline the AuNSL data model, editor functionality, and describe our approach to sharing our data via existing and emerging standards such as Darwin Core and Taxon Concept Schema (TCS2). We then describe what we, as consumers of taxonomic data from published works, really need from publishers of new, and reprocessed historical data. In brief, we need structured taxonomic data conforming to an adequate standard.
The Australian National Species List (AuNSL) is the provider of names and taxonomy for significant national biodiversity data infrastructures including the Atlas of Living Australia, the Terrestrial ...Ecosystem Research Network, the Biodiversity Data Repository, and the Species Profile and Threats Database. The AuNSL mints persistent identifiers for names covered by the codes of nomenclature and name-like objects such as phrase names. To ensure sustainability of identifiers, a mapping service is provided to always resolve all AuNSL identifiers including historical and deprecated forms. Names are used as the building blocks for recording taxon name usages and taxon concepts. We provide services for matching, disambiguation and taxonomic resolution of names.
The AuNSL does not exist in a vacuum and supports identifier mappings to external resources and related systems such as the International Plant Name Index (IPNI), Zoobank, the Biodiversity Heritage Library. To enable this integration, persistent identifiers from original and/or significant sources are required and this data is currently limited and incomplete within the AuNSL. To address this issue, we need to look backwards for improved ways of matching to existing persistent identifiers and forward to improving capture of taxonomic novelties and name-like objects and their identifiers.
Despite the extraordinary significance leaves have for life on Earth, their origin and development remain vigorously debated. More than a century of paleobotanical, morphological, and phylogenetic ...research has still not resolved fundamental questions about leaves. Developmental genetic data are sparse in ferns, and comparative studies of lycophytes and seed plants have reached opposing conclusions on the conservation of a leaf developmental program.
We performed phylogenetic and expression analyses of a leaf developmental regulator (Class III HD-Zip genes; C3HDZs) spanning lycophytes and ferns.
We show that a duplication and neofunctionalization of C3HDZs probably occurred in the ancestor of euphyllophytes, and that there is a common leaf developmental mechanism conserved between ferns and seed plants. We show C3HDZ expression in lycophyte and fern sporangia and show that C3HDZs have conserved expression patterns during initiation of lateral primordia (leaves or sporangia). This expression is maintained throughout sporangium development in lycophytes and ferns and indicates an ancestral role of C3HDZs in sporangium development.
We hypothesize that there is a deep homology of all leaves and that a sporangium-specific developmental program was coopted independently for the development of lycophyte and euphyllophyte leaves. This provides molecular genetic support for a paradigm shift in theories of lycophyte leaf evolution.
Ash trees (genus Fraxinus, family Oleaceae) are widespread throughout the Northern Hemisphere, but are being devastated in Europe by the fungus Hymenoscyphus fraxineus, causing ash dieback, and in ...North America by the herbivorous beetle Agrilus planipennis. Here we sequence the genome of a low-heterozygosity Fraxinus excelsior tree from Gloucestershire, UK, annotating 38,852 protein-coding genes of which 25% appear ash specific when compared with the genomes of ten other plant species. Analyses of paralogous genes suggest a whole-genome duplication shared with olive (Olea europaea, Oleaceae). We also re-sequence 37 F. excelsior trees from Europe, finding evidence for apparent long-term decline in effective population size. Using our reference sequence, we re-analyse association transcriptomic data, yielding improved markers for reduced susceptibility to ash dieback. Surveys of these markers in British populations suggest that reduced susceptibility to ash dieback may be more widespread in Great Britain than in Denmark. We also present evidence that susceptibility of trees to H. fraxineus is associated with their iridoid glycoside levels. This rapid, integrated, multidisciplinary research response to an emerging health threat in a non-model organism opens the way for mitigation of the epidemic.
It is well known that ethylene regulates a diverse set of developmental and stress-related processes in angiosperms, yet its roles in early-diverging embryophytes and algae are poorly understood. ...Recently, it was shown that ethylene functions as a hormone in the charophyte green alga Spirogyra pratensis. Since land plants evolved from charophytes, this implies conservation of ethylene as a hormone in green plants for at least 450 million years. However, the physiological role of ethylene in charophyte algae has remained unknown. To gain insight into ethylene responses in Spirogyra, we used mRNA sequencing to measure changes in gene expression over time in Spirogyra filaments in response to an ethylene treatment. Our analyses show that at the transcriptional level, ethylene predominantly regulates three processes in Spirogyra: (1) modification of the cell wall matrix by expansins and xyloglucan endotransglucosylases/hydrolases, (2) down-regulation of chlorophyll biosynthesis and photosynthesis, and (3) activation of abiotic stress responses. We confirmed that the photosynthetic capacity and chlorophyll content were reduced by an ethylene treatment and that several abiotic stress conditions could stimulate cell elongation in an ethylene-dependent manner. We also found that the Spirogyra transcriptome harbors only 10 ethylene-responsive transcription factor (ERF) homologs, several of which are regulated by ethylene. These results provide an initial understanding of the hormonal responses induced by ethylene in Spirogyra and help to reconstruct the role of ethylene in ancestral charophytes prior to the origin of land plants.
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