REAP1/AtSWAP70 Integrates RAB5 and ROP Signaling During Sexual Reproduction

Small GTPases of the Ras superfamily are critical regulators of diverse cellular processes. While cross-talk between their signaling pathways has been documented in animals, similar mechanisms remain unexplored in plants, where small GTPases have undergone unique evolutionary diversification. Here, we identify REAP1/AtSWAP70 as a novel effector in Arabidopsis thaliana that interacts with the active forms of both canonical RAB5 and the plant-specific RAB5, ARA6. Remarkably, REAP1 also binds to active ROP7, a plant-unique Rac-type GTPase, via its DH domain. REAP1 localizes to endosomes and facilitates ROP7 recruitment from the plasma membrane, a process dependent on RAB5 activity. Genetic analyses reveal that the RAB5-REAP1-ROP7 signaling cascade is essential for gametogenesis, impacting pollen viability and development. This study provides the evidence of functional cross-talk between RAB and ROP signaling in plants, unveiling a novel layer of regulatory complexity in plant GTPase signaling during plant reproduction.