Studies On Transcription Factor PsSKN7 And Two RXLR Effectors In Phytophthora Sojae

Phytophthora sojae is a major challenge to the production of soybean in the world. Plant resistance is currently the major control method for P.sojae root rot on soybean. However,resistant cultivars can promote the buildup of new virulent populations.Naturally virulent populations have been recovered from cultivated fields and natural areas;these infestations have resulted in the failure of resistant soybean cultivars.Learning the mechanism underlying the development stages and pathogenicity of P.sojae will help researches to find new targets of chemical control and provide good ideas for designing new control strategies.Reactive oxygen burst and subsequent disarrangement of redox homeostasis are key responsive events that regulate plant-pathogen interaction.For the host,it represents one important defense strategy;for the pathogen,it stands as one obstacle which must be overcome to succeed in infection.In yeasts,SKN7 is a transcription factor contributing to the oxidative stress response.Through bio-informatics screening,a skn7 homologue from Phytophthora sojae was isolated and designated as PsSKN7.Continuous expression of PsSKN7 in yeast can induce cell death.But lower expression of PsSKN7 in the mutant skn7Δwhich was particularly sensitive to oxidative stress and acute heat shock,could rescue growth arrest under these conditions,and increase the resistance of wild type to acute heat shock.These results indicated active roles of PsSKN7 in anti-oxidation.Recent evidence indicates that the RXLR-dEER motif is indeed required for targeting these oomycete effectors into host plant cells.We bioinformatically identify almost 350 candidate effector genes in the genomes of Phytophthora sojae.However,the contributions of these effectors to pathogenicity remain poorly understood.We use PVX expression system and yeast expression system to identify the function of the P.sojae RXLR-dEER effector proteins Avr1b and Avh331.We find that Avr1b can suppress programmed cell death(PCD) induced by H₂O₂ in the Saccharomyces cerevisiae.We also find that Avr1b and Avh331 can suppress PCD triggered by the mouse BAX protein in yeast and Nicotiana benthamiana cells.Avh331 and BAX may interact with each other through yeast two hybrid system.Thus,our results indicate that some RXLR-dEER effector can induce plant susceptibility to P.sojae infection by inhibiting host PCD.