Function And Mechanism Of RxLR Effector Avh52 From Phytophthora Sojae

Soybean root rot caused by Phytophthora sojae is one of destructive diseases to soybean production,causing around $1-2 billion in losses per year worldwide.About 400 RxLR(Arg-any amino acid-Leu-Arg)effectors are secreted by Phytophthora sojae during pathogen infection,and it is important to affect plant immunity for these effectors.These effectors promote plant susceptibility with procedural expression and cooperative effect,of which some can induce plant immnity and some can supress plant defense.Based on previous studies in our lab,PsAvh52 P.sojae-secreted inhibited the cell death induced by PAMPs(INF1 and XEG1)and effectors(PsAvh238 and PsAvh241).On this basis,the virulent function of PsAvh52 was comprehensively explored.The molecular mechanism of PsAvh52 to promote Phytophthora infection was explained by identificating the target of it.The virulent function of RxLR effector PsAvh52 is analyzed.In this study,the expression level of PsAvh52 is persistently high and PsAvh52 is essential for full virulence of P.sojae on soybean.The polymorphism of the sequences between the four Phytophthora strains representing the races is analyzed and 7 positive selection loci are found,which belongs to big sequence variation.This indicates that genetic variation of PsAvh52 hanppened under a large host selection pressure,when PsAvh52 played a virulent factor.Protein sequence analysis found that PsAvh52 has a typical NLS(nuclear localization signal)domain on the C-terminal of protein by SMART,except conservative SP(signal peptide)and RxLR-dEER motif in RxLR effector.Expression of PsAvh52 in soybean hairy root and N.benthamiana,it localized in plant nucleus,which indicated PsAvh52 played an important role in plant cell nucleus.PsAvh52-RFP-expressing P.sojae infecting to soybean,PsAvh52-RFP localized in the haustoria in infected plant cells.PsAvh52-knoekout transformant showed impaired virulence on soybean compared to WT.Expression of GFP-PsAvh52 in soybean hairy roots or N.benthamiana promoted Phytophthora infection.To identificate the virulent motif of PsAvh52 to promote infection,PsAvh52 and mutants were expressed in N.benthamiana and then leaves were infected by P.capsici,which showed that NLS and 69-86 motif are essential for its virulence.These data suggest that PsAvh52 is an essential virulence factor that can enhance Phytophthora infection.To identificate host target of PsAvh52 and analyze the function of target.Expression of GFP-PsAvh52 in soybean hairy roots or N.benthamiana promoted Phytophthora infection,which indicated PsAvh52 played a virulent factor to promote infection.Identificating host target of PsAvh52 makes clear that how PsAvh52 disturbs plant immunity.The host target protein GmTAP1 of PsAvh52 was identificated by Co-IP and LC-MS/MS.PsAvh52 interaction with GmTAP1 was determined using Co-IP and Pull down,but PsAvh52 can not interact with homologous protein GmTAP2.This indicated that PsAvh52 interact with GmTAP1 specially.Besides,the biological function GmTAPl and GmTAP2 is different:(1)GmTAP1 localized in plant cytoplasm,but GmTAP2 localized in nucleus and cytoplasm.(2)GmTAP1,a negatively imlune regulator,modulates soybean resistance to P.sojae,but GmTAP2 don’t affect plant immunity.TAP proteins exist:in plants,but not in animals.The conserved HAT(histone acetyltransferase)domain is found in the C terminal of plant TAP proteins,but the N-terminal differ.The different N terminals result in the different the function of these homologous proteins in soybean and Arabidopsis.In all,the target protein GmTAP1 of PsAvh52,with HAT enzyme activity,regulated plant immunity during P.sojae interaction with soybean.PsAvh52 modulated the GmTAP1-mediated plant immunity.Increasing evidence suggested that epigenetic modifications including histone acetylation are an important mediator of plant defenses during plant-pathogen interactions.However,how effectors secreted by plant pathogens disturb or co-opt host epigenetic modifications to promote infection has not been thoroughly explored.In this study,we found that PsAvh52 could bind.to soybean acetyltransferase,GmTAP1,causing it to re-localize from the cytoplasm to nucleus,a process that required the PsAvh52 NLS as well as protein-protein interactions domains on both PsAvh52 and GmTAP1.In addition,nuclear-localized GmTAP1 increased the level of histone H2AK5 and H3K9 acetylation and enhanced plant susceptibility,both of which required the histone acetyltransferase enzyme activity of GmTAP1.Together,these results indicate that PsAvh52 recruits GmTAP1 to promote plant susceptibility through epigenetic modifications.