RabA- and RabE-mediated trafficking define distinct branches of plant pre-invasive immunity

Abstract

Pre-invasive immunity constitutes a major barrier to disease and protects plants against the vast majority of filamentous fungal and oomycete pathogens through localized defence responses at sites of attempted invasion. Although membrane trafficking is essential for these responses, demonstrated by the requirement for the syntaxins PEN1 and SYP122, the underlying trafficking pathways remain poorly understood. Here, we show that trafficking mediated by the RabE and RabA GTPase subfamilies defines two functionally distinct branches of plant pre-invasive immunity. Inhibition of RabE rapidly compromised immunity to powdery mildew fungi, including the durable immunity conferred by mlo mutations, and reduced focal accumulation of PEN1 at papillae without substantially affecting callose deposition. By contrast, inhibition of RabA disrupted plasma membrane localization of multiple proteins and preferentially compromised immunity to the oomycete pathogen Phytophthora infestans. Together, these findings support a model in which RabE promotes the powdery mildew-specific function of PEN1 in pre-invasive immunity, whereas RabA contributes to a broader defence pathway associated with the shared function of PEN1 and SYP122. Our results support a model in which pre-invasive immunity is coordinated by specialized trafficking modules with distinct pathogen requirements and establish RabA- and RabE-mediated trafficking as defining components of these pathways.