The function of two trypsin-like serine proteases from Eriocheir sinensis involved in Spiroplasma eriocheiris infection.

Abstract Trypsin-like serine proteases (TLSPs), are members of the serine protease family and play important roles in innate immune responses. There are no previous studies regarding the role of TLSPs in immune responses to Spiroplasma eriocheiris in Eriocheir sinensis. In this paper, two TLSPs were identified from E. sinensis , namely EsTLSP-I and EsTLSP-II. Phylogenetic analysis showed that EsTLSP-I and EsTLSP-II clustered into two different groups that the crustaceans within each group were specifically. Tissue distribution analysis indicated that both EsTLSP-I and EsTLSP-II were mostly expressed in hemocytes, in the gill and in the intestine. The EsTLSP-I and EsTLSP-II transcription levels in hemocytes significantly increased after infection with S. eriocheiris. After dsRNA interference, the expression of both EsTLSP-I and EsTLSP-II distinctively declined from 48 h to 96 h. The expression of proPO and beta-1,3-glucan binding protein (LGBP) were also notably reduced after silencing. Compared to the control group, the copy number of S. eriocheiris increased significantly in interfering EsTLSP-I and EsTLSP-II groups during S. eriocheiris infection. Meanwhile, the mortality of crabs in the silenced EsTLSP-I and EsTLSP-II groups was higher than in the control group after the S. eriocheiris challenge. The results indicate that EsTLSP-I and EsTLSP-II play important roles in the innate immune system of Eriocheir sinensis, in combating infections of S. eriocheiris. Highlights • EsTLSP-I and EsTLSP-II were involved in the immune responses of E. sinensis to S. eriocheiris challenge. • EsTLSP-I and EsTLSP-II are part of the innate immnue system activating the proPO system. • The copies of S. eriocheiris and crabs' death rate were notably increased in EsTLSP-I and EsTLSP-II RNAi assay. [ABSTRACT FROM AUTHOR]