Smt3 is required for the immune response of silkworm, Bombyx mori.

SUMO works in a similar way as ubiquitin to alter the biological properties of a target protein by conjugation. The homologous gene of SUMO named BmSmt3 was identified for the first time in silkworm. The expression of BmSmt3 was enhanced in the fat body of silkworm after immune challenge. However, the expression of BmSmt3 after immune challenge was almost invariant in silk gland, which is the nonimmune organ in silkworm. In addition, the expression of BmRelA and CecropinB1 was decreased significantly in pupae after the BmSmt3 was knocked down in vivo. According to our results, BmSmt3 might participate in the immune response through regulating the expression of BmRelA gene, which can further regulate the expression of antibacterial peptide subsequently in silkworm.