Effect of glycogen synthase and glycogen phosphorylase knockdown on the expression of glycogen- and insulin-related genes in the rice brown planthopper Nilaparvata lugens

Nilaparvata lugens is a serious threat to rice growth. Glycogen metabolism is one of the important physiological processes of insects, which is mainly regulated by glycogen synthase (GS) and glycogen phosphorylase (GP). In the present study, trehalose content was significantly reduced at 72 h after NlGP and NlGS knockdown, whereas glucose content was significantly increased at both 48 h and 72 h after GS knockdown. RNAi combined with RNA-Seq was used to identify NIGP- and NlGS-related pathways and genes in N. lugens. A total of 593 genes were up-regulated and 5969 genes were down-regulated after NlGP and NlGS knockdown, respectively. Moreover, the NlGS-knockdown group was mapped to 10,967 pathways, whereas the NlGP-knockdown group was mapped to 7948 pathways, and the greatest differences between the groups were associated with carbohydrate, lipid, amino acid and energy metabolism. Meanwhile, 1800, 1217, and 1211 transcripts in the NlGP-knockdown group and 2511, 1666, and 1727 transcripts in the NlGS-knockdown group were involved in bioprocess, cellular ingredients and molecular function, respectively. Almost all these genes were down-regulated by either NlGP or NlGS knockdown, with significant down-regulation of the 6-trehalose phosphate synthase (TPS), trehalase (TRE), GS, GP, phosphoacetylglucosamine mutase (PGM, n = 2), Insulin receptors (InRs) and insulin-like peptides (lips) genes. These results have demonstrated that RNAi-mediated NlGP and NlGS knockdown could lead to content of trehalose and glucose out of balance, but have no obvious effect on glycogen content, and have suggested that GS plays more complex role in other metabolism pathway of N. lugens.