AP3M harbors actin filament binding activity that is crucial for vacuole morphology and stomatal closure in Arabidopsis

Significance Actin filament dynamics and the proper functioning of adaptor complexes are required for the sorting of cargo proteins from the Golgi to the vacuole, but the relationship between these 2 important processes remains unclear. We show that AP3M, the medium (μ) subunit of the AP3 complex, directly binds to actin filaments at a conserved domain and severs the actin filaments in vitro. In addition, we show that the F-actin binding activity of AP3M is important for the cargo sorting mediated by the AP3 complex and for proper vacuole morphology. We propose that the proper functioning of AP3M in regulating F-actin dynamics is important for stomatal closure in Arabidopsis thaliana .