Inhibition of plant apoplastic immune subtilases: of pathogen or plant origin?
D. SUELDO (1), T. Hong (1), S. Ninck (2) (1) University of Oxford, United Kingdom; (2) Universität Duisburg-Essen, Germany

Apoplastic immune proteases play an instrumental role in plant defence against invading pathogens. P69 is an abundant apoplastic serine protease of the subtilase family whose accumulation is increased during pathogen attack, though their role in plant defence it is still unclear. Activity-Based Protein Profiling (ABPP) is a technique that allows monitoring of protein activities without previous knowledge of substrates. Using ABPP we have detected that the activity of apoplastic P69-like subtilases is suppressed in N. benthamiana upon infection by Pseudomonas syringae pv. tomato (Pto) by an inhibitor that is larger than 3kDa and heat-stable. To determine the identity of the inhibitor, apoplastic fluid obtained from Pto-infected N. benthamiana leaves, which contains the inhibitor, was fractionated by gel filtration. Fractions were tested for the presence of subtilase-inhibitory activity using competitive ABPP and analysed by mass spectrometry to determine their protein composition. In parallel, immunoprecipitation assays are performed to identify proteins that bind NbP69, the most abundant P69-like subtilase in apoplastic fluid of N. benthamiana suppressed upon Pto infection. Preliminary results of both strategies will be presented at this meeting. With these experiments we aim at identifying and disabling the suppression mechanism of apoplastic subtilases in wild tobacco during infection with Pto to reveal their true role in plant defence.

Abstract Number: P17-618
Session Type: Poster