Plasmodesmata dynamics in bryophyte model organisms: secondary formation and developmental modifications of structure...

Area of Science:

• Plant Biology
• Cell Biology
• Evolutionary Biology

Background:

• Plasmodesmata (PD) are crucial for symplasmic communication in all land plants.
• Angiosperm development involves extensive remodeling of PD networks, including the formation of secondary PD (secPD).
• Information on PD dynamics in bryophytes, sister groups to angiosperms, is limited.

Purpose of the Study:

• To investigate the structural and functional modifications of PD during the development of key bryophyte model organisms.
• To compare PD dynamics in bryophytes with those in angiosperms to understand evolutionary conservation.
• To explore the role of PD networks in the meristems of hornwort sporophytes.

Main Methods:

• Quantitative electron microscopy was used to analyze PD structure in developing tissues of *Anthoceros agrestis* (hornwort), *Physcomitrium patens* (moss), and *Marchantia polymorpha* (liverwort).
• Fluorescence redistribution after photobleaching (FRAP) was employed to assess PD permeability in *P. patens*.
• PD networks in *A. agrestis* sporophyte meristems were examined and compared to angiosperm meristems.

Main Results:

• SecPD formation via twinning, resulting in PD pairs or branched structures, was observed in gametophytes of all studied bryophytes, indicating this is an ancient mechanism.
• Bryophyte gametophytes exhibit taxon-specific PD modifications, including enlarged diameters and pit pairs, potentially to maintain transport rates.
• PD permeability was significantly reduced in maturing *P. patens* phyllids, similar to angiosperm leaves.
• Targeted secPD formation was identified in the multi-initial meristems of *A. agrestis* sporophytes, resembling features of angiosperm meristems.

Conclusions:

• Plasmodesmata structure and function are differentially modified during bryophyte development.
• PD twinning is an ancient evolutionary mechanism for adjusting PD numbers.
• Plasmodesmata networks in hornwort sporophyte meristems share characteristics with angiosperm meristems, suggesting potential homologous origins and conserved signaling roles.