Kinesin ARK2 coordinates PIN2 trafficking and nanoclustering to mediate root gravitropism in Arabidopsis

Gravitropism guides plant growth by perceiving gravity, with root responses dependent on auxin redistribution mediated by PIN-FORMED (PIN) transporters. However, how the cytoskeleton regulates the polar maintenance of PIN2, particularly its plasma membrane (PM) nanodomains organization during root gravitropism, remain largely understudied. Here, we identify Armadillo Repeat Kinesin 2 (ARK2) as a positive regulator of root gravitropic growth. We revealed that ARK2 ensures auxin asymmetry and gravitropic response through two mechanisms: it mediates microtubule-dependent vesicular trafficking of PIN2 to sustain its PM abundance, and directly interacts with PIN2 to promote its nanodomains assembly and restrict lateral diffusion at the PM. Together, these dual functions sustain PIN2 polar distribution, which is essential for establishing auxin asymmetry during gravitropic responses. Our study uncovers a kinesin-mediated regulatory mechanism governing PIN2 dynamics and nanoclustering, bridging the gap in understanding cortical cytoskeletal control of PIN2 nanoclustering in root gravitropism.