The BIR2/BIR3-Associated Phospholipase D gamma 1 Negatively Regulates Plant Immunity(1)([OPEN])

摘要

Plants have evolved effective strategies to defend themselves against pathogen invasion. Starting from the plasma membrane with the recognition of microbe-associated molecular patterns (MAMPs) via pattern recognition receptors, internal cellular signaling pathways are induced to ultimately fend off the attack. Phospholipase D (PLD) hydrolyzes membrane phospholipids to produce phosphatidic acid (PA), which has been proposed to play a second messenger role in immunity. The Arabidopsis (Arabidopsis thaliana) PLD family consists of 12 members, and for some of these, a specific function in resistance toward a subset of pathogens has been shown. We demonstrate here that Arabidopsis PLD gamma 1, but not its close homologs PLD gamma 2 and PLD gamma 3, is specifically involved in plant immunity. Genetic inactivation of PLD gamma 1 resulted in increased resistance toward the virulent bacterium Pseudomonas syringae pv. tomato DC3000 and the necrotrophic fungus Botrytis cinerea. As pld gamma 1 mutant plants responded with elevated levels of reactive oxygen species to MAMP treatment, a negative regulatory function for this PLD isoform is proposed. Importantly, PA levels in pld gamma 1 mutants were not affected compared to stressed wild-type plants, suggesting that alterations in PA levels are not likely the cause for the enhanced immunity in the pld gamma 1 line. Instead, the plasma-membrane-attached PLD gamma 1 protein colocalized and associated with the BAK1-INTERACTING RECEPTOR-LIKE KINASES BIR2 and BIR3, which are known negative regulators of pattern-triggered immunity. Moreover, complex formation of PLD gamma 1 and BIR2 was further promoted upon MAMP treatment. Hence, we propose that PLD gamma 1 acts as a negative regulator of plant immune responses in complex with immunity-related proteins BIR2 and BIR3.