Biology subjects

Roetzer, J.

Publications and source records attributed to Roetzer, J..

4 recordsLinked to original sources

bioRxiv2026

PHOTOTROPIN-mediated blue light signaling orients the asymmetry of Marchantia polymorpha spores

Multicellular organisms produced by sexual reproduction develop from single cells and the asymmetry of these cells can define the orientation of the earliest developmental axes. The haploid multicellular stage of the plant, Marchantia polymorpha, develops from a single cell - the spore - that divides asymmetrically, producing an apical germ cell that generates the plant body and a smaller basal cell that differentiates as an anchoring germ rhizoid cell. We show that the orientation of this asymmetric cell division is controlled by an external, environmental cue - blue light - that is perceived by the photoreceptor PHOTOTROPIN and signals in an NCH1-dependent manner. This defines core elements of the mechanism by which a directional environmental signal orients cell division, which in turn orients the first axis of symmetry.

plant biology↗

bioRxiv2025

Antagonism between blue and red light-signalling controls thallus flatness in Marchantia polymorpha

The growth orientation of the Marchantia polymorpha thallus - a system of dorsiventralized, indeterminate axes - is modulated by light. We show that red and blue light act antagonistically to control thallus growth tropisms, with red light signalling promoting epinasty and blue light signalling promoting hyponasty. We found that loss-of-function mutations in the blue light receptor MpPHOT led to epinasty, while loss-of-function mutations in the red light receptor MpPHY resulted in hyponasty. We hypothesize that these antagonistic activities of blue and red light signalling are balanced in white light, resulting in the development of flat thalli. Using time-resolved transcriptomics, we identified genes that were rapidly induced upon light exposure. Among these genes were all six members of the M. polymorpha BBX gene family. Mutants harbouring loss-of-function mutations in two of the six MpBBX transcription factors developed defective thallus tropisms. Mpbbx1 loss-of-function mutants formed hyponastic thalli, while Mpbbx5 loss-of-function mutants developed epinastic thalli. Double mutants Mpbbx1 Mpbbx5 grew flat, supporting the hypothesis that they function antagonistically. Together, these data indicate that phototropin-mediated blue light and phytochrome-mediated red light signalling antagonistically modulate thallus tropism, and that BBX transcription factors also act antagonistically to regulate thallus flatness.

plant biology↗

bioRxiv2024

Population genomics of Marchantia polymorpha subspecies ruderalis reveals evidence of climate adaptation

Sexual reproduction results in the development of haploid and diploid cell states during the life cycle. In bryophytes the dominant multicellular haploid phase produces motile sperm that swim through water to the egg to effect fertilization from which a relatively small diploid phase develops. In angiosperms, the reduced multicellular haploid phase produces non-motile sperm that is delivered to the egg through a pollen tube to effect fertilization from which the dominant diploid phase develops. These different life cycle characteristics are likely to impact the distribution of genetic variation among populations. However, little is known about the distribution of genetic variation among populations of bryophytes. To understand how genetic variation is distributed among populations of a bryophyte and to establish the foundation for population genetics research in bryophytes, we described the genetic diversity of collections of Marchantia polymorpha subspecies ruderalis, a cosmopolitan ruderal liverwort. We explored genetic diversity of this species using 78 genetically unique (non-clonal) accessions from a total of 209 collected from 37 sites in Europe and Japan. There was no detectable population structure among European populations but significant genetic differentiation between Japanese and European populations. By associating genetic variation across the genome with global climate data, we identified summer temperature and precipitation as climate factors influencing the frequency of adaptative alleles. We speculate that the requirement for water through which motile sperm swim imposes a constraint on the life cycle to which the plant genetically adapts.

plant biology↗

bioRxiv2022

Meristem dormancy in a dichotomous branching system is regulated by a liverwort-specific miRNA and a clade III SPL gene in Marchantia polymorpha

The shape of modular organisms depends on branching architecture, which in plants is determined by the fates of generative centres called meristems. The branches of the liverwort Marchantia polymorpha are derived from two adjacent meristems that develop at thallus apices. These meristems may be active and develop branches or may be dormant and do not form branches. The relative number and position of active and dormant meristems defines overall shape and form of the thallus. We show that the clade III SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) transcription factor, MpSPL1, is required for meristem dormancy. The activity of MpSPL1 is regulated by the liverwort-specific Mpo-MR13 miRNA which in turn is regulated by PIF-mediated phytochrome signaling. An unrelated miRNA, MIR156, represses a different SPL gene (belonging to clade IV) that inhibits branching during the shade avoidance response in Arabidopsis thaliana. This suggests that a conserved mechanism of phytochrome signaling modulates branching architecture in liverworts and angiosperms and therefore likely operated in the last common ancestor. However, PIF-mediated phytochrome signaling represses the expression of different miRNA genes with different SPL targets during dichotomous, apical branching in liverworts and during lateral, subapical branching in angiosperms. We speculate that the mechanism that acts downstream of light and regulates meristem dormancy evolved independently in liverworts and angiosperms.

plant biology↗