Staff Research Associate University of California, San Diego San Diego, California
Body of Abstract: Morphogenesis requires precise coordination of cell division and growth, but how these are coupled to create plant tissues remains mysterious. To investigate this underlying regulation, we have interrogated the mechanisms controlling a previously unidentified polarized division field in the Arabidopsis leaf epidermis. Asymmetric and symmetric cell divisions across the leaf surface establish the pattern of stomata. Multiple pathways converge to regulate the orientation of the asymmetric divisions, but little is known about the cellular mechanisms that control the final symmetric cell division (SCD) that creates paired guard cells. By mapping division patterns across Arabidopsis cotyledons and true leaves, we uncovered a cryptic division field that orients SCDs along the proximodistal leaf axis. SCD alignment is developmentally regulated, locally aligned to immediate neighbors and, unexpectedly, conserved across a range of eudicots. By identifying mutants that perturb this orientation field, we implicate morphological parameters at both the cellular and tissue scales as key regulatory inputs. Strikingly, mutants that perturb leaf shape through distinct pathways exhibit predictable orientation defects, suggesting that cell division is coordinated by supracellular growth. In support of this hypothesis, we have seen that acute, local stress modifies the alignment of neighboring SCDs. In ongoing work, we are refining our understanding of how mechanics facilitate the alignment by probing the coordinated growth mechanics of whole leaves with those of individual cells. Taken together, we have uncovered a novel polarized division field in stomatal progenitors which establishes the orientation of these essential two-cell pores that mediate interactions between the plant and its environment. Continued exploration of this field will delineate how the behaviors of individual plant cells are linked to growth dynamics of whole tissues.