Sumoylation of Nosema bombycis is essential to its proliferation in silkworm, Bombyx mori

Abstract

• NbSUMO was successfully cloned and was highly conserved in fungi . • NbSUMO was essential to the proliferation of Nosema Bombycis . • 65 silkworm proteins and 10 Nb proteins may be modified by NbSUMO. Small ubiquitin-like modifier (SUMO) is an important post-translational modification protein, which plays an important role in regulating the function of substrate proteins. The purpose of this study is to explore the function of the SUMO gene in Nosema bombycis (Nb). The SUMO gene of Nb ( NbSUMO ) was successfully cloned and the sequence analysis showed that the amino acid sequence of NbSUMO has a low identity with SUMOs from Homo sapiens and Bombyx mori . Cluster analysis showed that all SUMOs from microsporidium were clustered on the same large branch, and NbSUMO had the highest homology with Nosema pernyi . Real-time fluorescence quantitative PCR (RT-qPCR) analysis showed that the expression of NbSUMO was significantly increased after Nb infection, while the expression of SUMO gene in Bombyx mori ( BmSUMO ) was not, suggesting that Nb relies on its own SUMO modification system to promote proliferation. When the NbSUMO was knocked down by RNA interference (RNAi), the DNA copy of the Nb genome was significantly decreased suggesting NbSUMO was essential to the proliferation of Nb. eGFP-NbSUMO was expressed in BmN cells of Bombyx mori by constructing the recombinant Bombyx mori nucleopolyhedrovirus (BmNPV). Pull-down and mass spectrometry analysis found that 65 silkworm proteins and 10 Nb proteins may bind to NbSUMO, involving in ubiquitin-dependent protein catabolic process, regulation of transcription, apoptotic process, and other biological processes. The study demonstrated that NbSUMO is a typical SUMO family protein. And Nb expresses a large amount of NbSUMO to modify substrate proteins, thus participating in the proliferation of Nb.