Arabidopsis RabGDIs mediate Rab targeting and are crucial for male gametophytic function

Rab GTPases are key regulators of vesicular trafficking, not only switching between active and inactive forms but also cycling between donor/resident and target membranes, a process regulated by factors including guanine nucleotide dissociation inhibitors (RabGDIs), whose function is largely unknown in plants. By reverse genetic approaches, we demonstrate that Arabidopsis RabGDIs redundantly mediate male fertility such that the functional loss of RabGDIs compromises pollen development, germination, and directional growth of pollen tubes. By combining cellular and pharmacological approaches, we demonstrate that RabGDIs are critical for the targeting of Rab GTPases not only in secretory but also in vacuolar pathways. Vacuolar trafficking regulators such as Rab5 and Rab7 GTPases are mis-targeted to the apical plasma membrane of pollen tubes due to the functional loss of RabGDIs, hinting at a phylum-specific role of RabGDIs also in the initial targeting of Rab GTPases to their donor/resident membrane.