REAP1/AtSWAP70 integrates RAB5 and ROP signalling during sexual reproduction.

Small GTPases of the Ras superfamily are critical regulators of diverse cellular processes. While crosstalk between their signalling 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 an 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 Dbl homology 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 signalling cascade is essential for gametogenesis, impacting pollen viability and development. This study provides evidence of functional crosstalk between RAB and ROP signalling in plants, unveiling a layer of regulatory complexity in plant GTPase signalling during plant reproduction.