Conserved key players required for Physcomitrella patens male fertility are affected by accumulation of (epi-) mutations

Physcomitrella patens belongs to the bryophytes and is an extant species of the first land plants. This phylogenetic informative position allows the analysis of key evolutionary steps in (land) plant evolution employing P. patens as a model organism. Decades of research mainly focused on the gametophytic generation, probably also due to the lack of sexual reproductive events in the primarily used ecotype Gransden. Long term in vitro vegetative reproduction probably led to the accumulation of somatic (epi-) mutations which eventually led to a nearly male sterile phenotype. So far, only few P. patens ecotypes are used for scientific work. Thus, to overcome the fertility issues and to apply comparative analyses to study sexual reproduction and sporophyte development as well as species and population divergence in P. patens, the establishment of more ecotypes is highly needed. In comparison to other plant model organisms as e.g. Arabidopsis thaliana, genome wide epigenetic modifications especially with regard to sexual reproduction are still barely studied in P. patens ecotypes. Here I present the characterization of the sexual reproduction of the recently introduced fertile ecotype Reute which was collected 2006 in Germany. Reute is the most closely related ecotype to Gransden reported so far. In a comparative analysis between the ecotypes Gransden, Reute and Villersexel, I could show no differences in timing and morphology of the sexual reproductive tissues. However, while Reute was as fertile as the more distant ecotype Villersexel, Gransden was nearly self-sterile. Also, I present the fluorescent marker strain Reute-mCherry which can be used in crossing analyses e.g. to determine if female or male sexual reproductive organs are impaired. By employing this method, a clear male defect could be shown in Gransden. Further, I present a comparative multi-omics analysis between Gransden and Reute using different tissues during sexual reproduction. Single nucleotide polymorphisms (SNPs), DNA-methylation and RNA-expression pinpoint a flagellar defect, which presumably leads to the observed male fertility impairment in Gransden. Finally, I present the characterization of key-players which are highly conserved within eukaryotes and are required for flagellar motility in humans as well as in the moss P. patens

ABA-Induced Vegetative Diaspore Formation in Physcomitrella patens

The phytohormone abscisic acid (ABA) is a pivotal regulator of gene expression in response to various environmental stresses such as desiccation, salt and cold causing major changes in plant development and physiology. Here we show that in the moss Physcomitrella patens exogenous application of ABA triggers the formation of vegetative diaspores (brachycytes or brood cells) that enable plant survival in unfavorable environmental conditions. Such diaspores are round-shaped cells characterized by the loss of the central vacuole, due to an increased starch and lipid storage preparing these cells for growth upon suitable environmental conditions. To gain insights into the gene regulation underlying these developmental and physiological changes, we analyzed early transcriptome changes after 30, 60, and 180 min of ABA application and identified 1,030 differentially expressed genes. Among these, several groups can be linked to specific morphological and physiological changes during diaspore formation, such as genes involved in cell wall modifications. Furthermore, almost all members of ABA-dependent signaling and regulation were transcriptionally induced. Network analysis of transcription-associated genes revealed a large overlap of our study with ABA-dependent regulation in response to dehydration, cold stress, and UV-B light, indicating a fundamental function of ABA in diverse stress responses in moss. We also studied the evolutionary conservation of ABA-dependent regulation between moss and the seed plant Arabidopsis thaliana pointing to an early evolution of ABA-mediated stress adaptation during the conquest of the terrestrial habitat by plants

Conserved key players required for Physcomitrella patens male fertility are affected by accumulation of (epi-) mutations

Physcomitrella patens belongs to the bryophytes and is an extant species of the first land plants. This phylogenetic informative position allows the analysis of key evolutionary steps in (land) plant evolution employing P. patens as a model organism. Decades of research mainly focused on the gametophytic generation, probably also due to the lack of sexual reproductive events in the primarily used ecotype Gransden. Long term in vitro vegetative reproduction probably led to the accumulation of somatic (epi-) mutations which eventually led to a nearly male sterile phenotype. So far, only few P. patens ecotypes are used for scientific work. Thus, to overcome the fertility issues and to apply comparative analyses to study sexual reproduction and sporophyte development as well as species and population divergence in P. patens, the establishment of more ecotypes is highly needed. In comparison to other plant model organisms as e.g. Arabidopsis thaliana, genome wide epigenetic modifications especially with regard to sexual reproduction are still barely studied in P. patens ecotypes. Here I present the characterization of the sexual reproduction of the recently introduced fertile ecotype Reute which was collected 2006 in Germany. Reute is the most closely related ecotype to Gransden reported so far. In a comparative analysis between the ecotypes Gransden, Reute and Villersexel, I could show no differences in timing and morphology of the sexual reproductive tissues. However, while Reute was as fertile as the more distant ecotype Villersexel, Gransden was nearly self-sterile. Also, I present the fluorescent marker strain Reute-mCherry which can be used in crossing analyses e.g. to determine if female or male sexual reproductive organs are impaired. By employing this method, a clear male defect could be shown in Gransden. Further, I present a comparative multi-omics analysis between Gransden and Reute using different tissues during sexual reproduction. Single nucleotide polymorphisms (SNPs), DNA-methylation and RNA-expression pinpoint a flagellar defect, which presumably leads to the observed male fertility impairment in Gransden. Finally, I present the characterization of key-players which are highly conserved within eukaryotes and are required for flagellar motility in humans as well as in the moss P. patens

DEK1 displays a strong subcellular polarity during Physcomitrella patens

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DEK1 displays a strong subcellular polarity during Physcomitrella patens 3D growth

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A vertically transmitted amalgavirus is present in certain accessions of the bryophyte Physcomitrium patens

In the last few years, next-generation sequencing techniques have started to be used to identify new viruses infecting plants. This has allowed to rapidly increase our knowledge on viruses other than those causing symptoms in economically important crops. Here we used this approach to identify a virus infecting Physcomitrium patens that has the typical structure of the double-stranded RNA endogenous viruses of the Amalgaviridae family, which we named Physcomitrium patens amalgavirus 1, or PHPAV1. PHPAV1 is present only in certain accessions of P. patens, where its RNA can be detected throughout the cell cycle of the plant. Our analysis demonstrates that PHPAV1 can be vertically transmitted through both paternal and maternal germlines, in crosses between accessions that contain the virus with accessions that do not contain it. This work suggests that PHPAV1 can replicate in genomic backgrounds different from those that actually contain the virus and opens the door for future studies on virus–host coevolution.This work was supported by grants from the Spanish Ministerio de Economía, Industria y Competitividad (AGL2016-78992-R/FEDER) and Ministerio de Ciencia e Innovación (PID2019-106374RB-I00/AEI/10.13039/501100011033) to JMC. The IJPB benefits from the support of the LabEx Saclay Plant Sciences (SPS) (ANR-10-LABX-0040-SPS).Peer reviewe