Abstract
The vesicle trafficking SYNTAXIN OF PLANTS132 (SYP132) drives hormone-regulated endocytic traffic to suppress the density and function of plasma membrane (PM) H+-ATPases. In response to bacterial pathogens, it also promotes secretory traffic of antimicrobial pathogenesis-related (PR) proteins. These seemingly opposite actions of SYP132 raise questions about the mechanistic connections between the two, likely independent, membrane trafficking pathways intersecting plant growth and immunity. To study SYP132 and associated trafficking of PM H+-ATPase 1 (AHA1) and PATHOGENESIS-RELATED PROTEIN1 (PR1) during pathogenesis, we used the virulent Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) bacteria for infection of Arabidopsis (Arabidopsis thaliana) plants. SYP132 overexpression suppressed bacterial infection in plants through the stomatal route. However, bacterial infection was enhanced when bacteria were infiltrated into leaf tissue to bypass stomatal defenses. Tracking time-dependent changes in native AHA1 and SYP132 abundance, cellular distribution, and function, we discovered that bacterial pathogen infection triggers AHA1 and SYP132 internalization from the plasma membrane. AHA1 bound to SYP132 through its regulatory SNARE Habc domain, and these interactions affected PM H+-ATPase traffic. Remarkably, using the Arabidopsis aha1 mutant, we discovered that AHA1 is essential for moderating SYP132 abundance and associated secretion of PR1 at the plasma membrane for pathogen defense. Thus, we show that during pathogenesis SYP132 coordinates AHA1 with opposing effects on the traffic of AHA1 and PR1.