Formin nanoclustering-mediated actin assembly during plant flagellin and DSF signaling

Plants respond to bacterial infection acutely with actin remodeling during plant immune responses. The mechanisms by which bacterial virulence factors (VFs) modulate plant actin polymerization remain enigmatic. Here, we show that plant-type-I formin serves as the molecular sensor for actin remodeling in response to two bacterial VFs: Xanthomonas campestris pv. campestris (Xcc) diffusible signal factor (DSF), and pathogen-associated molecular pattern (PAMP) flagellin in pattern-triggered immunity (PTI). Both VFs regulate actin assembly by tuning the clustering and nucleation activity of formin on the plasma membrane (PM) at the nano-sized scale. By being integrated within the cell-wall-PM-actin cytoskeleton (CW-PM-AC) continuum, the dynamic behavior and function of formins are highly dependent on each scaffold layer's composition within the CW-PM-AC continuum during both DSF and PTI signaling. Our results reveal a central mechanism for rapid actin remodeling during plant-bacteria interactions, in which bacterial signaling molecules fine tune plant formin nanoclustering in a host mechanical-structure-dependent manner. Ministry of Education (MOE) Nanyang Technological University Published version S.M. is supported by a Margdarshi Fellowship (IA/M/15/1/502018) from the DBT-Wellcome Trust Alliance and the Department of Atomic Energy (Government of India) under project no. RTI 4006 to National Centre for Biological Sciences, India. This study was supported by an NTU startup grant (M4081533) and the Singapore Ministry of Education (MOE) tiers 1 (RG32/20) and 3 (MOE2019-T3-1-012) to Y.M.