Abstract
The silkworm is an oligophagous insect for which mulberry leaves are the sole diet. The nutrients needed for vital activities of the egg, pupal, and adult stages, and the proteins formed in the cocoon, are all derived from the larval stages. The silkworm feeds and grows quickly during the larval stages. In particular, the amount of leaf ingested and digested quickly increases from the ecdysis to the gluttonous stage in the fifth instar period. In this study, we used the iTRAQ proteomic technique to identify and analyze silkworm larval digestive juice proteins during this period. A total of 227 proteins were successfully identified. These were primarily serine protease activity, esterase activity, binding, and serine protease inhibitors, which were mainly involved in the digestion and overcoming the detrimental effects of mulberry leaves. Moreover, 30 genes of the identified proteins were expressed specifically in the midgut. Temporal proteomic analysis of digestive juice revealed developmental dynamic features related to molecular mechanisms of the principal functions of digesting, resisting pathogens, and overruling the inhibitory effects of mulberry leaves protease inhibitors (PIs) with a dynamic strategy, although overruling the inhibitory effects has not yet been confirmed by previous study. These findings will help address the potential functions of digestive juice in silkworm larvae.
Highlights
The silkworm, Bombyx mori, is a complete metamorphosis insect
Among the 227 identified proteins, there were serine proteases, serine protease inhibitors, 9 carboxypeptidases, 9 aminopeptidases, 7 lipases, 6 lipoproteins, 4 collagenases, 6 immune-related proteins, 12 enzymes involved in nucleic acid metabolism, 10 enzymes involved in sugar metabolism, and 22 uncharacterized proteins (Table S1)
The nutrients needed for the vital activities of egg, pupal, and adult stages, and the proteins formed in the cocoon, are derived from the larval stage
Summary
The silkworm, Bombyx mori, is a complete metamorphosis insect. It is a domestic insect of economic significance, and a model insect of Lepidoptera, which is widely used in basic and applied research [1,2]. The silkworm is an oligophagous insect and mulberry leaves are its sole diet [3]. The digestive tube can be divided into the foregut, midgut, and hindgut according to its function and structure [4]. The main functions of the foregut are physical digestion, consisting of feeding, grinding, swallowing, and temporary storage of mulberry leaves. The midgut is the most important section and comprises approximately 78 percent of the total length of the digestive tube. The main functions of the midgut are chemical digestion focused on digesting and absorbing with the action of enzymes in digestive juice
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