Two Novel Kunitz Effector Proteins Using Different Infection and Survival Strategies to Suppress Immunity in Pine.

Pine wilt disease, caused by , results in tremendous economic loss in conifer production every year. To disturb the host immune responses, plant pathogens secrete a mass of effector proteins that facilitate the infection process. Although several effectors of have been identified, detailed mechanisms of their functions remain largely unexplored. Here, we reveal two novel Kunitz effectors, named BxKU1 and BxKU2, using different infection strategies to suppress immunity in . We found that both BxKU1 and BxKU2 could suppress PsXEG1-triggered cell death and were present in the nucleus and cytoplasm in . However, they had different three-dimensional structures and various expression patterns in infection. In situ hybridization experiments showed that was expressed in the esophageal glands and ovaries, whereas was only expressed in the esophageal glands of females. We further confirmed that the morbidity was significantly decreased in infected with when and were silenced. The silenced but not , affected the reproduction and feeding rate of . Moreover, BxKU1 and BxKU2 targeted to different proteins in , but they all interacted with thaumatin-like protein 4 (TLP4) according to yeast two-hybrid screening. Collectively, our study showed that could incorporate two Kunitz effectors in a multilayer strategy to counter immune response in , which could help us better understand the interaction between plant and .