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Dual Role of Serine Protease Homolog BmSPH-1 in Development and Immunity of the Silkworm Bombyx mori
In insects, serine proteases are involved in a variety of physiological processes including digestion, development, and immunity. Bombyx mori serine protease homolog BmSPH-1 regulates nodule melanization and is recruited into nodules from the hemolymph by B. mori lipopolysaccharide-binding protein. Here, we show the dual role of BmSPH-1 in development and immunity of B. mori. BmSPH-1 was expressed in the hemocytes during larval-pupal transformation and localized to the cuticle of silkworms, which indicates that BmSPH-1 is secreted from hemocytes and then transported to the cuticle via the hemolymph. BmSPH-1 was proteolytically activated in the cuticle during larval-pupal transformation and the early pupal stage. BmSPH-1 RNAi resulted in the arrest of larval-pupal transformation and pupal cuticular melanization. Furthermore, the expression of BmSPH-1 was up-regulated in the hemocytes during infection. Taken together, we found that BmSPH-1 is involved in larval-pupal transformation and pupal cuticular melanization as well as the innate immunity of silkworms, which indicates that BmSPH-1 is responsible for either development or immunity.
