|dc.description.abstract||Plant cells exhibit a variety of shapes and sizes that underlie their functions. These distinctive geometries are dictated by cell walls. The region adjoining two adjacent faces of a cell is termed a cell edge. Having varying degrees of curvature, cell edges play a fundamental role in defining the shape and geometry of the cell. Edge curvature is thus an important point of regulation in cell morphogenesis, and increasing evidence suggests a large compliment of proteins—edge proteins— resides at cell edges to control cell edge stiffness and curvature.
To understand cell edge properties, I identified additional edge proteins— Microtubule-Associated Protein 65-3 (MAP65-3), Phragmoplast Orienting Kinesin1 (POK1), BRICK1 (BRK1), Actin-related protein-2 (Arp2) and MUSTACHES. The project then focused on BRICK1 (BRK1), an actin nucleation-promoting factor.
Here, by examining BRK1 localization pattern and its regulation on the cell edges, I identified feedbacks between BRK1 and cell edges. On the one hand, cell edge curvature influences the accumulation of BRK1 to the edge. BRK1 exhibits a preferential enrichment at high-curvature cell edges. The localization pattern is gradually changed from uniform to specific enrichment as edge curvature change. On the other hand, BRK1 protein itself regulate cell edge through microtubule. In the absence of BRK1, fewer anticlinal microtubule bundles (AMBs) form, CMT tend to strongly align in parallel and change orientation more frequently. Collectively, these defects may explain cell lobe reduction in the brk-1 mutant. Moreover, the brk-1 mutants also exhibit cell plate orientation defects, which could result from failed asymmetric division.
Besides, additional functions were observed too. A series of preliminary results suggest an association between BRK1 and Plasmodesmata (PD). BRK1 signal localizes in the pit field at the anticlinal wall, where PD accumulate.
In summary, cell edges affect BRK1 localization through curvature changes, while BRK1 modulates cell edge curvature through MTs at both the cell division and cell expansion levels.||