The evolution of plasmodesmata

• Applicant: Dr. Katrin Ehlers
• Subject Area: Developmental Biology ; Cell Biology
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 440525456

Plasmodesmata (PD) control intercellular communication in plants and estabilish a direct symplasmic continuity between adjacent cells across the cell walls. For seed plants, it is well known that the PD networks within tissues are highly dynamic and undergo sophisticated structural and functional modifications in a precisely regulated manner. These changes play essential roles in the regulation of plant development, as well as in metabolic adaptations to changing environmental conditions, and in the coordinaton of cell- or non-cell autonomous pathogen defense. PD do regularly occur in non-seed plants, and they have also been found in some groups of the streptophyte algae, which are closely related to all land plants. Thus, it has been assumed that intercellular communication via PD has already had an impact on plant evolution during the conquest of land. PD connectivity might have been a prerequisite for the increasing complexity of the plant bodies allowing division of labour between spatially patterned cells, tissues, and organs. Further, PD might have been essential for the adaptation to the hazardous conditions on land, when plant tissues have had to develop coordinated mechanisms to face a multitude of abiotic and biotic stresses. This raises the central question whether PD and symplasmic network have kept the same properties and the same regulatory circuits from the very beginning on, or whether there was an "evolution of PD" in the course of land plant evolution over hundreds of million of years, allowing an increasingly complex regulation of intercellular communication?This question remains open, since there is only scarce and partly contradictory information available on the plasmodesmal networks in streptophyte algae and non-seed plants that could be compared to a bulk of findings on seed plants. This is why we want to study the evolution of plasmodesmata in the present project. Before asking molecular questions, we will gather more information on the structural adaptations that PD and PD networks have experienced in the course of evolution. Thus, we will use transmission electron microscopy and confocal laser scanning microscopy to answer, e.g., the following questions: -- are typical PD substructures, derived from the endoplasmic reticulum, already present in PD of streptophyte algae?-- are there differences in the complexity of symplasmic networks in hornworts and thalloid liverworts that reflect the distinct complexibility of their vegetative bodies?-- do the same mechanisms of PD modifications take place during "leaf" development of non- seed plants that have been found for seed plants? Although not all "leaf" organs are homologous?-- do all non-seed plants form secondary PD in already existing walls? And which mechanism(s) do they use?

• DFG Programme: Priority Programmes
• Subproject of: SPP 2237: MAdLand — Molecular Adaptation to Land: plant evolution to change