A Phytophthora capsici RXLR Effector Targets and Inhibits a Plant,PPlase to Suppress Endoplasmic Reticulum-Mediated Immunity

Phytophthora pathogens secrete a large arsenal of effectors that manipulate host processes to create an environment conducive to pathogen colonization. However, the underlying mechanisms by which Phytophthora effectors manipulate host plant cells still remain largely unclear. In this study, we report that PcAvr3a12, a Phytophthera capsici RXLR effector and a member of the Avr3a effector family, suppresses plant immunity by targeting and inhibiting host plant peptidyl-prolyl cis-trans isomerase （PPlase）. Overexpression of PcAvr3a 12 in Arabidopsis thaliana enhanced plant susceptibility to P. capsici. FKBP15-2, an endoplasmic reticulum （ER）-Iocalized protein, was identified as a host target of PcAvr3a12 during early P. capsici infection. Analyses of A. thaliana T-DNA insertion mutant （fkbp15-2）, RNAi, and overexpression lines consistently showed that FKBP15-2 positively regulates plant immunity in response to Phytophthora infection. FKBP15-2 possesses PPlase activity essential for its contribution to immunity but is directly suppressed by PcAvr3a12. Interestingly, we found that FKBP15-2 is involved in ER stress sensing and is required for ER stress-mediated plant immunity. Taken together, these results suggest that P. capsici deploys an RXLR effector, PcAvr3a12, to facilitate infection by targeting and suppressing a novel ER-Iocalized PPlase, FKBP15-2, which is required for ER stress-mediated plant immunity.

Engineering crop Phytophthora resistance by targeting pathogen-derived PI3P for enhanced catabolism

Phytophthora pathogens lead to numerous economically damaging plant diseases worldwide,including potato late blight caused by P.infestans and soybean root rot caused by P.sojae.Our previous work showed that Phytophthora pathogens may generate abundant phosphatidylinositol 3-phosphate(PI3P)to promote infection via direct association with RxLR effectors.Here,we designed a disease control strategy for metabolizing pathogen-derived PI3P by expressing secreted Arabidopsis thaliana phosphatidylinositol-4-phosphate 5-kinase 1(AtPIP5K1),which can phosphorylate PI3P to PI(3,4)P2.We fused AtPIP5K1 with the soybean PR1a signal peptide(SP-PIP5K1)to enable its secretion into the plant apoplast.Transgenic soybean and potato plants expressing SP-PIP5K1 showed substantially enhanced resistance to various P.sojae and P.infestans isolates,respectively.SP-PIP5K1 significantly reduced PI3P accumulation during P.sojae and soybean interaction.Knockout or inhibition of PI3 kinases(PI3Ks)in P.sojae compromised the resistance mediated by SP-PIP5K1,indicating that SP-PIP5K1 action requires a supply of pathogen-derived PI3P.Furthermore,we revealed that SP-PIP5K1 can interfere with the action of P.sojae mediated by the RxLR effector Avr1k.This novel disease control strategy has the potential to confer durable broad-spectrum Phytophthora resistance in plants through a clear mechanism in which catabolism of PI3P interferes with RxLR effector actions.

Intracellular and Extracellular Phosphatidylinositol 3-Phosphate Produced by Phytophthora Species Is Important for Infection

RxLR effectors produced by Phytophthora pathogens have been proposed to bind to phosphatidylinositol 3-phosphate （Ptdlns（3）P） to mediate their translocation into host cells and/or to increase their stability in planta. Since the levels of Ptdlns（3）P in plants are low, we examined whether Phytophthora species may produce Ptdlns（3）P to pro- mote infection. We observed that Ptdlns（3）P-specific GFP biosensors could bind to P. parasitica and P. sojae hyphae dur- ing infection of Nicotiana benthamiana leaves transiently secreting the biosensors, suggesting that the hyphae exposed Ptdlns（3）P on their plasma membrane and/or secreted Ptdlns（3）R Silencing of the phosphatidylinositol 3-kinases （PI3K） genes, treatment with LY294002, or expression of Ptdlns（3）pobinding proteins by P. sojae reduced the virulence of the pathogen on soybean, indicating that pathogen-synthesized Ptdlns（3）P was required for full virulence. Secretion of Ptdlns（3）P-binding proteins or of a PI3P-5-kinase by N. benthamiana leaves significantly increased the level of resist- ance to infection by P. parasitica and P. capsici. Together, our results support the hypothesis that Phytophthora species produce external Ptdlns（3）P to aid in infection, such as to promote entry of RxLR effectors into host cells. Our results derived from P. sojae RxLR effector Avrlb confirm that both the N-terminus and the C-terminus of this effector can bind Ptdlns（3）P.

The Phytophthora effector Avh241 interacts with host NDR1-like proteins to manipulate plant immunity

Plant pathogens rely on effector proteins to suppress host innate immune responses and facilitate colonization.Although the Phytophthora sojae RxLR effector Avh241 promotes Phytophthora infection,the molecular basis of Avh241 virulence remains poorly understood.Here we identified non-race specific disease resistance 1(NDR1)-like proteins,the critical components in plant effector-triggered immunity(ETI)responses,as host targets of Avh241.Avh241 interacts with NDR1 in the plasma membrane and suppresses NDR1-participated ETI responses.Silencing of GmNDR1s increases the susceptibility of soybean to P.sojae infection,and overexpression of GmNDR1s reduces infection,which supports its positive role in plant immunity against P.sojae.Furthermore,we demonstrate that GmNDR1 interacts with itself,and Avh241 probably disrupts the self-association of GmNDR1.These data highlight an effective counter-defense mechanism by which a Phytophthora effector suppresses plant immune responses,likely by disturbing the function of NDR1 during infection.