Insight into the Interactions Between GhXI-K and Rab GTPases in Cotton Fiber

Myosin XI-K plays an important role in cell expansion and polarized growth, acting as a motor protein that drives organelle trafficking and cytoplasmic streaming. To elucidate the molecular mechanisms of myosin XI-K’s role in the polarized growth of cotton fiber, we investigated the interactions between GhXI-K and Rab GTPases in cotton (Gossypium hirsutum). Protein docking analyses based on AlphaFold3 predicted that GhXI-K interacted with eight Rab GTPases. A total of 37 interaction residues were identified in GhXI-K, of which 5 crucial contact residues were located in the globular tail domain (GTD) and 2 were located in the motor domain. Key interaction residues in the Rab GTPases were also found to be located in conserved regions: switch-I and switch-II. Yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assays confirmed the predictions and showed that these interactions occur primarily in the GTD and the motor domain. Our findings reveal that GhXI-K interacts with Rab GTPases through both the motor and tail domains, suggesting a synergistic mechanism that facilitates polarized vesicle trafficking in cotton fiber cells.