Abstract
Rab GTPases regulate tethering and fusion of transport vesicles to the target membranes in membrane traffic by acting as a molecular switch through cycling between the GDP- and GTP-bound states. Rab5 has been shown in mammalian cells to perform various functions in the endocytic pathway such as regulation of fusion and dynamics of endosomes. Endocytosis has recently been found to play fundamental roles also in plant cells, which include regulation of PIN localization and brassinosteroid signaling. Molecular mechanisms and functions of endocytosis are now being investigated actively, which has also been revealing functions of plant Rab5s at molecular and cellular levels. However, biological importance of Rab5 at organ and whole-plant levels has hardly been examined thus far. VPS9a is the sole guanine nucleotide exchange factor for Rab5 in Arabidopsis thaliana, which activates all three Rab5 proteins. Using A. thaliana vps9a-2 mutant, we are studying physiological roles of RAB5 activation in plant development. Our results suggest that proper activation of RAB5 plays important roles in radial cell patterning, establishment of cell identity, and cell elongation.
