PLD? Reduces The Protein Level Of RPM1 To Negatively Regulate Its Function

Plants develop immunity system to confront invasion of pathogens.Plant immune system consists of PTI(PAMP-triggered immunity)and ETI(Effector triggered immunity).Recognition of PAMPs(Pathogen-associated molecular pattern)by PRRs(Pattern recognition receptors)activates PTI,which typically occurs on plasma membrane and undertakes activation of pathogenesis related(PR)proteins.ETI consists of resistance(R)proteins,usually polymorphic NB-LRR proteins that specifically perceive pathogenic effectors and induce strong and rapid defense response.The most classic model of ETI is guard model of RIN4(RPM1 interacting protein 4)protein.RPM1(Resistance to Pseudomonas syringae pv.maculicola 1)is activated after perceiving specific threonine phosphorylation of RIN4 in the presence of the Pseudomonas syringae type III effector AvrRpm1 or AvrB.Plant disease resistance protein RPM1 guards RIN4 protein in Arabidopsis.RIN4 plays as a positive factor in RPM1 mediated signaling pathway.Phospholipase D(PLD)has lipolytic activity and hydrolyzes membrane phospholipids to produce phosphatidic acid(PA)and a free-head alcohol.PLD family in Arabidopsis contains 12 members,and plays an important role in plant responses to both abiotic and biotic stresses.The activation of RPM1 stimulates the activity of PLD to increase the amount of PA which can induce hypersensitive response(HR).We cloned all the members of PLD family to determine their interactions with RPM1.Results from both Co-IP and BIFC assays indicated that PLD? interacts with RPM1.Overexpression of PLD? suppresses RPM1-mediated disease resistance and HR response in Arabidopsis.We also found that overexpression of PLD? can reduce the membrane association of RPM1 and consequently reduces the protein level of RPM1.We treated the plants with ABA to stimulate the enzymic activity of PLD to determine whether the activity of PLD is required to affect the protein level of RPM1.The results showed that ABA treatment reduced the protein level of RPM1,and the inhibitor of PLD activity suppressed this effect,suggesting the activity of PLD is necessary to reduce the protein level of RPM1.We provide a model to demonstrate that the activated PLD not only mediates the signal transduction of RPM1,but it also negatively restricts the function of RPM1 to conrol the signal output of plant immunity.This is the first research to determine that the PLD activity can affect the protein level of immune receptor RPM1 and the function of RPM1.Because many abiotic stresses can affect the enzymetic activity of PLD,our resrach suggests a potenial regulation point for plants to integrate different stresses.