Despite their key phylogenetic position and their unique biology, hornworts have been widely overlooked. Until recently there was no hornwort model species amenable to systematic experimental investigation. We have developed an High transformation efficiency was achieved by using thallus tissue grown under low light conditions. We generated a total of 274 transgenic The transformation technique described here should pave the way for detailed molecular and genetic studies of hornwort biology, providing much needed insight into the molecular mechanisms underlying symbiosis, carbon‐concentrating mechanism, RNA editing and land plant evolution in general.
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Summary Anthoceros agrestis has been proposed as the model species to study hornwort biology.Agrobacterium ‐mediated method for the stable transformation ofA. agrestis , a hornwort model species for which a genetic manipulation technique was not yet available.A. agrestis lines expressing the β‐glucuronidase (GUS), cyan, green, and yellow fluorescent proteins under control of the CaMV 35S promoter and several endogenous promoters. Nuclear and plasma membrane localization with multiple color fluorescent proteins was also confirmed. -
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Premise Phylogenetic trees of bryophytes provide important evolutionary context for land plants. However, published inferences of overall embryophyte relationships vary considerably. We performed phylogenomic analyses of bryophytes and relatives using both mitochondrial and plastid gene sets, and investigated bryophyte plastome evolution.
Methods We employed diverse likelihood‐based analyses to infer large‐scale bryophyte phylogeny for mitochondrial and plastid data sets. We tested for changes in purifying selection in plastid genes of a mycoheterotrophic liverwort (
Aneura mirabilis ) and a putatively mycoheterotrophic moss (Buxbaumia ), and compared 15 bryophyte plastomes for major structural rearrangements.Results Overall land‐plant relationships conflict across analyses, generally weakly. However, an underlying (unrooted) four‐taxon tree is consistent across most analyses and published studies. Despite gene coverage patchiness, relationships within mosses, liverworts, and hornworts are largely congruent with previous studies, with plastid results generally better supported. Exclusion of
RNA edit sites restores cases of unexpected non‐monophyly to monophyly forTakakia and two hornwort genera. Relaxed purifying selection affects multiple plastid genes in mycoheterotrophicAneura but notBuxbaumia . Plastid genome structure is nearly invariant across bryophytes, but thetuf A locus, presumed lost in embryophytes, is unexpectedly retained in several mosses.Conclusions A common unrooted tree underlies embryophyte phylogeny, [(liverworts, mosses), (hornworts, vascular plants)]; rooting inconsistency across studies likely reflects substantial distance to algal outgroups. Analyses combining genomic and transcriptomic data may be misled locally for heavily
RNA ‐edited taxa. TheBuxbaumia plastome lacks hallmarks of relaxed selection found in mycoheterotrophicAneura . Autotrophic bryophyte plastomes, includingBuxbaumia , hardly vary in overall structure. -
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Summary Extant land plants consist of two deeply divergent groups, tracheophytes and bryophytes, which shared a common ancestor some 500 million years ago. While information about vascular plants and the two of the three lineages of bryophytes, the mosses and liverworts, is steadily accumulating, the biology of hornworts remains poorly explored. Yet, as the sister group to liverworts and mosses, hornworts are critical in understanding the evolution of key land plant traits. Until recently, there was no hornwort model species amenable to systematic experimental investigation, which hampered detailed insight into the molecular biology and genetics of this unique group of land plants. The emerging hornwort model species,
Anthoceros agrestis , is instrumental in our efforts to better understand not only hornwort biology but also fundamental questions of land plant evolution. To this end, here we provide an overview of hornwort biology and current research on the model plantA .agrestis to highlight its potential in answering key questions of land plant biology and evolution. -
Phycobilisomes (PBS) are antenna megacomplexes that transfer energy to photosystems II and I in thylakoids. PBS likely evolved from a basic, inefficient form into the predominant hemidiscoidal shape with radiating peripheral rods. However, it has been challenging to test this hypothesis because ancestral species are generally inaccessible. Here we use spectroscopy and cryo-electron microscopy to reveal a structure of a “paddle-shaped” PBS from a thylakoid-free cyanobacterium that likely retains ancestral traits. This PBS lacks rods and specialized ApcD and ApcF subunits, indicating relict characteristics. Other features include linkers connecting two chains of five phycocyanin hexamers (CpcN) and two core subdomains (ApcH), resulting in a paddle-shaped configuration. Energy transfer calculations demonstrate that chains are less efficient than rods. These features may nevertheless have increased light absorption by elongating PBS before multilayered thylakoids with hemidiscoidal PBS evolved. Our results provide insights into the evolution and diversification of light-harvesting strategies before the origin of thylakoids.more » « lessFree, publicly-accessible full text available December 1, 2024
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Endosymbiotic associations between hornworts and nitrogen-fixing cyanobacteria form when the plant is limited for combined nitrogen (N). We generated RNA-seq data to examine temporal gene expression patterns during the culturing of N-starved Anthoceros punctatus in the absence and the presence of symbiotic cyanobacterium Nostoc punctiforme. In symbiont-free A. punctatus gametophytes, N starvation caused downregulation of chlorophyll content and chlorophyll fluorescence characteristics as well as transcription of photosynthesis-related genes. This downregulation was reversed in A. punctatus cocultured with N. punctiforme, corresponding to the provision by the symbiont of N 2 -derived NH 4 + , which commenced within 5 days of coculture and reached a maximum by 14 days. We also observed transient increases in transcription of ammonium and nitrate transporters in a N. punctiforme–dependent manner as well as that of a SWEET transporter that was initially independent of N 2 -derived NH 4 + . The temporal patterns of differential gene expression indicated that N. punctiforme transmits signals that impact gene expression to A. punctatus both prior to and after its provision of fixed N. This study is the first illustrating the temporal patterns of gene expression during establishment of an endosymbiotic nitrogen-fixing association in this monophyletic evolutionary lineage of land plants. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .more » « less
