Plants and other organisms are able to tolerate stress, combat infection and maintain homeostasis through the conserved catabolic process of autophagy which involves sequestration of cytoplasmic material in double membraned vesicles for degradation and recycling. Understanding how autophagy is initiated and regulated is critical to gaining insight into many essential cellular processes such as development, aging and immunity against intracellular pathogens. In this study I show that a plant RabGTPase activating protein, Rab3GAPL, directly interacts with the autophagy adaptor protein ATG8CL through a canonical ATG8 interacting motif (AIM) to suppress autophagy in an AIM and catalytic Arg479 dependent manner. Furthermore, I show that Rab3GAPL interacts with and is a cognate GAP for the small RabGTPase Rab8a1 which plays a positive role in autophagosome biogenesis and flux. Finally, I elucidate that Rab3GAPL negatively affects immunity to the oomycete pathogen Phythophthora infestans but suppressing defence-related secretion immune responses mediated by Rab8a1. This thesis combines multiple approaches to functionally characterise a new plant RabGAP and its role in autophagy and immunity against invading pathogens. Furthermore, it provides evidence for extensive interactions between vesicle traffic components, autophagy and immunity in plants, paving the way for several new lines of inquiry into these processes.