The Heterodera glycines Effector Hg16B09 Suppresses Plant Innate Immunity

To test whether the effector Hg16 B09, identified from the soybean cyst nematode（SCN）, Heterodera glycines, plays an important role in manipulating host defense responses, we used Nicotiana benthamiana to transiently express recombinant Hg16 B09 plasmid, and different immune elicitors which can trigger defense responses（PTI and ETI）. Then, the effects of Hg16 B09 on PTI and ETI suppression were investigated by determining the reactive oxygen species（ROS） burst, hypersensitive response（HR）, and the expression of defense marker genes. Transient expression of Hg16 B09 in Nicotiana benthamiana leaves significantly suppressed the production of hydrogen peroxide and the expression levels of defense-related genes（PTI5, WRKY22-A, WRKY22-B and ACRE31） triggered by flg22. The transcript levels of PTI5, WRKY22-A,WRKY22-B and ACRE31 significantly decreased 45%, 61%, 67% and 61% in N. benthamiana leaves expressing Hg16 B09 when compared to that in the control leaves, respectively. Hg16 B09 could also inhibit HR induced by Pseudomonas syringae DC 3000 and an avirulent effector Rbp-1, which resulted in the smaller areas of cell death on the N. benthamiana leaves. qRT-PCR analysis further showed that Hg16 B09 caused significant down-regulation of defense genes in salicylic acid signaling during Pst DC3000 infection, and the expression levels of PR1 a, PR2, WRKY51 and PI1 induced by Pst DC3000 decreased approximately 67%, 71%, 48% and 81% in the leaves expressing Hg16 B09 compared to the control leaves, respectively. In conclusion, our data indicated that Hg16 B09 acts as PTI and ETI suppressors to perform its toxic biological functions during SCN-host interactions.