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 alpha and beta heterodimer and mediates cell interaction with extracellular matrix or other cells including microbial pathogens. A full length cDNA sequence (2862 bp) of a beta 1 subunit integrin (beta Se1) was cloned from the beet armyworm. Spodoptera exigua. Phylogenetic analysis showed that beta Se1 was clustered with other insect beta integrin subunits with the highest amino acid sequence identity (98.3%) to beta 1 of Spodoptera litura. Structural analysis of the deduced amino acid sequence indicated that beta Se1 possessed all functional domains known in other insect beta 1 integrins. RT-PCR analysis showed that beta Se1 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 beta Se1 RNA (dsRNA(beta se1)) into late instar S. exigua suppressed beta Se1 expression and resulted in significant reduction in pupal weight. The dsRNA(beta Se1) injection significantly impaired hemocyte-spreading and nodule formation of S. exigua in response to bacterial challenge. Furthermore, oral ingestion of dsRNA(beta Se1) induced reduction of beta Se1 expression in midgut and resulted in significant mortality of S. exigua during immature development. These results suggest that beta Se1 plays crucial roles in performing cellular immune responses as well as larval development in S. exigua. (C) 2011 Elsevier Ltd. All rights reserved.