Mechanism Of Plant Basal Defense Positively Regulated By Arabidopsis AIP4 Protein

In order to counteract the invasion of pathogenic microorganisms,plant have evolved two defensive layers.The first layer of plant immunity is called PAMP-triggered immunity(PTI),which is triggered upon the specifically perception of pathogen-associated molecular patterns(PAMPs).PAMPs are the conserved parts of pathogenic,such as flagella and EF-TU of bacteria.Pattern recognition receptors(PRRs)in the plasma membrane are in charge of recognizing those PAMPs to activate defense response,including deposition of callose and burst of reactive oxygen species,which can prevent the spread of pathogens and inhibit the growth.The second layer is called Effectors-triggered immunity(ETI).R protein in the host cells can specifically recognize effectors,thereby they activate more forceful immunity response than PTI.Furthermore,some previous research demonstrated there have some connections between PTI and ETI.We identified a unknonw protein named AIP4 in Arabidopsis thaliana that can interact with AvrB.Normally AIP4 located in nuclear,but a number of AIP4 could translocate to cytomembrane in presence of AvrB.We divided the sequence of AIP4 into three parts(N1,N2,C1).The C term of AIP4 named C1 could partly locate in membrane in absence of AvrB,and C1 interacted with AvrB and RIN4 powerfully in yeast two-hybrid system.Through injecting Pst DC3000(hrcC)into plants that overexpress AIP4 in the wild-type Col-0 background,we investigated that overexpression of AIP enhanced the ability of plant to defense Pst DC3000(hrcC),and increased the accumulation of callose and reactive oxygen species.Conversely,the mutant aip4 become more susceptible to Pst DC3000(hrcC).The result suggested that AIP4 positively regulates PTI.We infer that AIP4 involve in the suppression of AvrB to PTI.When AvrB invades into the host cell,it may associate with AIP4 or induce the transportation of AIP4 from nuclear to cytomembrane,decreasing the accumulation of AIP4 in nuclear which leads to the repression of AvrB to PTI.AIP4 includes a SANT domain which N1 and C1 don't occupy,but the interaction of N1 or C1 with AvrB was more strongly than the full length of AIP4.Meanwhile,N2 including SANT domain could not interact with AvrB.We infer that the SANT domain intrudes the interaction between AIP4 and AvrB.The discovery of AIP4 partly explains the mechanism which AvrB and RIN4 suppress PTI in plant.The result further proves that PTI and ETI own communication in signaling and substance.Moreover,it is significant that we investigate the characteristic phenomenon which AIP4 translocate in presence of AvrB.