Identification and analysis of genes differentially expressed in the Spodoptera litura fat body in response to the biocontrol fungus, Nomuraea rileyi

Nomuraea rileyi is an important pathogenic fungus that can successfully control Spodoptera litura. However, little is known on how S. litura responds to N. rileyi infection. A forward suppression subtractive hybridization (SSH) cDNA library was constructed from the S. litura fat body and the up-regulated genes were identified to isolate differentially expressed genes in response to N. rileyi. A total of 345/1175 random clones screened by cDNA array dot blotting were sequenced, resulting in 117 uniquely expressed sequence tags (ESTs). Potential functional genes were identified by BLAST searches and were categorized into seven groups associated with different biological processes based on the literature and gene ontologies. Among 117 genes, 74 had matches in the non-redundant (NR) protein database and were found to be involved in different biological processes, while 43 of the screened genes were classified to the “unknown function” gene group. Notably, only two genes had previously been reported in S. litura and most of the screened genes showed less similarity to known sequences based on BLASTn results, suggesting that 115 genes were found for the first time in S. litura. Semi-quantitative RT-PCR analysis of seven randomly selected genes revealed that most were differentially expressed after N. rileyi infection. qRT-PCR analysis confirmed that four genes (Hsp70, Hsp90, gallerimycin, and cysteine proteinase) were significantly up-regulated after N. rileyi infection. Taken together, the present study identified up-regulated S. litura genes in response to N. rileyi infection. Further investigations are needed to unravel the molecular mechanisms of the genes or proteins potentially involved in the S. litura innate immune defense against N. rileyi infection.