Identification and characterization of zero population growth (zpg) gene in Plutella xylostella

The diamondback moth (DBM), Plutella xylostella, is one of the most destructive insect pests on cruciferous plants, which causes huge economic losses annually across the world. Due to its resistance to all classes of insecticides, new effective management approaches are urgently needed. The innexin genes encode gap junction proteins in invertebrates, which play critical roles in cell-to-cell interactions for electrical currents, small molecules and ions. Zero population growth (zpg), one germline-specific innexin protein, is required for survival of differentiating early germ cells during gametogenesis in many insect species. In this study, nine innexin genes were identified from the P. xylostella genome, and named as Pxylinx1.1, Pxylinx1.2, Pxylinx2, Pxylinx3, Pxylinx4, Pxylinx7.1, Pxylinx7.2, PxylshakB.1 and PxylshakB.2. The expression profiles of P. xylostella innexin genes in different developmental stages and tissues were examined, revealing Pxylinx4 was specifically expressed in eggs and female ovaries, which is the candidate zpg gene in P. xylostella. RNA interference (RNAi) was utilized to investigate the functions of Pxylinx4 in egg-laying and egg-hatching. The results showed that RNAi treatment on Pxylinx4 in female P. xylostella, lead to the decrease of the egg-laying but not the egg-hatching. This study improves our understanding of P. xylostella innexin genes and provides a candidate molecular target (Pxylinx4) for developing new approaches to control this economically important pest.