A developmentally scheduled inhibitory polarity circuit centers the stomatal pore

Abstract

Symmetry in living systems often arises from coordinated asymmetries at smaller scales. The guard cells of stomata--bilaterally symmetric epidermal valves that mediate plant-atmosphere gas exchange--show coordinated asymmetries in pore placement and wall modification. Stomatal form and function are deeply conserved, yet molecular mechanisms defining coordinated cellular asymmetry are unknown. Here we show that pore position arises from a combination of pole avoidance and gradient centering in the membranes and wall dividing sister guard cells. Boundaries are established by spatiotemporal restriction of the receptor-like kinase MUSTACHES (MUS), which directs the disordered polarity protein OCTOPUS-LIKE2 (OPL2) to pore-forming regions. OPL2 peaks correspond to a focus of microtubules, and, from this position, the pore emerges. Experimental rewiring of the MUS-OPL2 polarity module profoundly impacts stomatal morphogenesis, eliminating, shifting, or even redirecting the pore to the opposite wall. These findings reveal a stomata-specific integration and elaboration of core polarity and centering programs, and challenge previous models of stomatal morphogenesis.