Identification of a gene family in Spodoptera exigua expressed in the midgut in response to pathogens: cross-talk between responses to Bt and to baculoviruses

The response of insects to pathogens involves changes in gene expression, which may help the insect to overcome the effects of pathogens or their toxins. In our current work, Suppression Subtractive Hybridization (SSH) was used to make cDNA-fragment libraries of genes that are up- or down-regulated in the midgut of last instar larvae of the beet armyworm, Spodoptera exigua, when exposed to the Bacillus thuringiensis (Bt) Cry1Ca toxin. Subsequent microarray studies using these libraries revealed altered gene expression levels for several genes in response to Bt toxin exposure. Among the genes upregulated after feeding with Bt toxins a new family of genes (Repat genes from ¿response to pathogen¿) was identified. cDNA¿s from four members of the Repat family were cloned and sequenced. Additional studies revealed that this gene family was also up-regulated during infection with the baculovirus Autographa californica (Ac) MNPV. A recombinant AcMNPV virus expressing Repat1 was constructed and used to infect S. exigua larvae. The pathogenicity of this Repat1 recombinant baculovirus was reduced ompared to the control confirming the role of Repat1 in reducing detrimental effects of pathogen infection in the larvae.