Abstract
Recent studies reveal that endocytosis is important for a variety of plant functions. However the underlying molecular mechanisms and the significance in plant development still remain largely unknown. Rab5, a subfamily of Rab GTPases, regulates a variety of endosomal functions as a molecular switch and key regulator of endocytosis. Mammalian Rab5 GTPase is known to regulate not only endosomal fusion but also signaling through endosomes. Rab GTPases are activated by specific guanine nucleotide exchange factors (GEFs), which accelerate the exchange of GDP for GTP. Vps9 domain, a catalytic core for activation of Rab5, is conserved in all Rab5 GEFs identified thus far. We have already demonstrated that the Arabidopsis VPS9a can activate all of three Arabidopsis Rab5 members (ARA6, ARA7, and RHA1). VPS9a comprises the conserved VPS9 domain at the N-terminus and a C-terminal region with no similarity to known domains. We found that truncation of the C-terminal region of VPS9a confers an increased GEF activity toward ARA6. Detailed functional analysis of the C-terminal region of VPS9a is now underway.
