PRL1 negatively regulates Rho GTPase-independent and -dependent signaling pathways maintaining actin microfilament dynamic for pavement cell morphogenesis

Actin dynamic is critical for cell morphogenesis in plants, but the signaling mechanisms underlying its regulation are not well understood. Here we found PRL1 (Pleiotropic Regulatory Locus1) modulates leaf pavement cell (PC) morphogenesis in Arabidopsis by maintaining the dynamic homeostasis of actin microfilaments (MF). Our previous studies indicated PC shape formation was mediated by the counteracting ROP2 and ROP6 signaling pathways that promote the organization of cortical MF and microtubules (MT), respectively. Our genetic screen for ROP6 enhancers identified prl1 alleles. Genetic analysis suggested that prl1 acted synergistically with ROP2 and ROP6 in regulation of PC morphogenesis. We further found that the activities of ROP2 and ROP6 were increased and decreased in prl1 mutants, respectively. Interestingly prl1 was found to prefer to depolymerize MF independent of ROP2 and ROP6. Stress (high salinity and low temperature) induced similar changes of ROP activities as do prl1 mutations. Together our findings provided evidence that PRL1 governed two signaling pathways that counteractively maintain actin dynamics and resultant cell morphogenesis.