RAB GTPases and their effectors in plant endosomal transport

The plant endomembrane system comprises distinctive membrane-bounded organelles connected with one another by the membrane trafficking system. The RAB GTPase is a key component of the membrane trafficking machinery that regulates the targeting and tethering of trafficking vesicles to target compartments by acting as a molecular switch cycling between active and inactive states. The functions of RAB GTPases are fulfilled through their interactions with several classes of interacting factors, including guanine nucleotide exchange factors (GEFs) and effector proteins. Effector proteins for plant RAB GTPases consist of evolutionarily conserved and plant-unique factors, which are involved in various membrane trafficking events in plant cells in ways unique to plants. In this review, we summarize recent findings on the functions of endosomal RAB GTPases that underwent unique diversification during plant evolution, with a special focus on RAB5/RABF and RAB11/RABA.