A bacterial cysteine protease effector protein interferes with photosynthesis to suppress plant innate immune responses

Abstract

SummaryThe bacterial pathogen Pseudomonas syringae pv tomato DC3000 suppresses plant innate immunity with effector proteins injected by a type III secretion system (T3SS). The cysteine protease effector HopN1, which reduces the ability of DC3000 to elicit programmed cell death in non-host tobacco, was found to also suppress the production of defence-associated reactive oxygen species (ROS) and callose when delivered by Pseudomonas fluorescens heterologously expressing a P. syringae T3SS. Purified His 6-tagged HopN1 was used to identify tomato PsbQ, a member of the oxygen evolving complex of photosystem II (PSII), as an interacting protein. HopN1 localized to chloroplasts and both degraded PsbQ and inhibited PSII activity in chloroplast preparations, whereas a HopN1D299A non-catalytic mutant lost these abilities. Gene silencing of NtPsbQ in tobacco compromised ROS production and programmed cell death by DC3000. Our data reveal PsbQ as a contributor to plant immunity responses and a target for pathogen suppression.

Reactive Oxygen Species and Plant Disease Resistance

“…HopN1, an effector protein of the bacterium P. syringae pv. tomato DC3000, was shown to localize to the thylakoids of chloroplasts where it bounds the PSII OEC protein PsbQ and promotes its degradation (Rodriguez-Herva et al 2012). The resulting interruption of PSII activity and suppression of ROS production compromised cell death during HR-type resistance and points to the role of chloroplastic PsbQ as a potential factor of antibacterial defense.…”

Effector Biology of Plant-Associated Organisms: Concepts and Perspectives

“…Some effectors, particularly bacterial T3SS effectors, are enzymes that biochemically modify host molecules, typically impeding their function or eliminating them (Cunnac et al 2009;Deslandes and Rivas 2012). The enzymatic activities of effectors are diverse and include protease, hydrolase, phosphatase, kinase, transferase, and ubiquitin ligase activities (Shao et al 2003;Abramovitch et al 2006b;Janjusevic et al 2006;Fu et al 2007;Lee et al 2012a;Rodriguez-Herva et al 2012;van Damme et al 2012). Other effectors do not carry enzymatic activities and act by binding host proteins to modulate their functions.…”

Organelle targeting during bacterial infection: insights from Listeria

“…Similar strategies are used by plant pathogens. For instance, the type III secretion system (T3SS) of Pseudomonas syringae pv tomato DC3000 secretes Hop1N, a cysteine protease targeted to the host chloroplast, and that interferes with photosynthesis by degrading a component of the photosystem, PsbQ [92]. This suppresses ROS production involved in the plant innate immune response to bacterial infection, and counteracts host programmed cell death.…”