Title: “Regulation of cell-to-cell communication during defense and development”

Speaker: Kyaw (Joe) Aung, GDCB assistant professor

Abstract: Regulated communication between cells is fundamental for multicellular organisms to function as a unit. Higher organisms utilize apoplastic and symplastic pathways to communicate between cells. The symplastic pathway allows molecules to move between adjoining cells through physical channels bridging the cells. In plants, plasmodesmata (PD) provide cytoplasmic and plasma-membrane continuity between adjoining cells for the symplastic movement, whereas gap junctions play similar roles in mammals. In our laboratory, we are interested in understanding the regulation of plasmodesmata during defense and development. Upon immune stimulation, plants close PD as part of their immune responses. We recently demonstrated that the bacterial pathogen Pseudomonas syringae deploy an effector protein, HopO1-1, to modulate PD function. Expression of HopO1-1 in Arabidopsis increases the distance of PD-dependent molecular flux between neighboring plant cells. HopO1-1 physically interacts with and destabilizes the plant PD-located protein PDLP5 and PDLP7. Both PDLPs are involved in bacterial immunity. Our findings reveal that a pathogenic bacterium utilizes an effector to manipulate PD-mediated host intercellular communication for maximizing the spread of bacterial infection. In addition to allowing signaling molecules to move between cells, PD also play critical roles in sugar translocation. In plants, mature leaves are major sites for photosynthesis, producing sugars. The sugars are then translocated to non-photosynthetic tissues of the plant via the phloem. Ectopic expression of PDLP5 and PDLP6 blocks the translocation of sugar at different cell types within mature leaves, leading to overaccumulation of starch and stunted growth. Interestingly, PDLP5 and PDLP6 express in non-overlapping cell types in leaves and roots. Starch overaccumulation patterns of 35S-PDLP5 and 35S-PDLP6 coincide with the cell types they express. The findings suggest that different members of PDLPs regulate the function of PD at specific cell-cell interfaces. Understanding the cell type-specific function of PDLPs will allow us to reveal how plant cells regulate the communication channels at different cell-cell junctions.

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