RNA interference of β1 integrin subunit impairs development and immune responses of the beet armyworm, Spodoptera exigua

Integrin is a cell surface protein that is composed of α and β heterodimer and mediates cell interaction with extracellular matrix or other cells including microbial pathogens. A full length cDNA sequence (2862 bp) of a β1 subunit integrin (βSe1) was cloned from the beet armyworm, Spodoptera exigua. Phylogenetic analysis showed that βSe1 was clustered with other insect β integrin subunits with the highest amino acid sequence identity (98.3%) to β1 of Spodoptera litura. Structural analysis of the deduced amino acid sequence indicated that βSe1 possessed all functional domains known in other insect β1 integrins. RT-PCR analysis showed that βSe1 was expressed in all developmental stages and all tested tissues of S. exigua. Its expression was further upregulated in hemocytes by injections of various microbes from quantitative RT-PCR analysis. Injection of double-stranded βSe1 RNA (dsRNAβSe1) into late instar S. exigua suppressed βSe1 expression and resulted in significant reduction in pupal weight. The dsRNAβSe1 injection significantly impaired hemocyte-spreading and nodule formation of S. exigua in response to bacterial challenge. Furthermore, oral ingestion of dsRNAβSe1 induced reduction of βSe1 expression in midgut and resulted in significant mortality of S. exigua during immature development. These results suggest that βSe1 plays crucial roles in performing cellular immune responses as well as larval development in S. exigua.