Cloning and expression of a JHA-inducible glutathione S-transferase gene in the common cutworm Spodoptera litura (Lepidoptera: Noctuidae)

The juvenile hormone titer during the last instar is a crucial determining switch for metamorphosis in lepidopterans. We previously observed that the induction of glutathione S-transferase (GST) activity by a juvenile hormone analog (JHA) is reversely proportional to the occurrence of JHA-induced supernumerary instars following topical application of JHA to Spodoptera litura during the last instar period. In this paper, at least five JHA-induced GSTs were purified by glutathione-affinity chromatography, and one was further isolated for determination of the N-terminal sequence. The corresponding cDNA was cloned and named SlGST1 (GenBank accession no. AY506545). SlGST1 was classified into the epsilon class of GSTs by phylogenetic analysis. Northern blot analyses further showed that the SlGST1 in fat bodies can be induced by JHA, particularly in 0-day-old sixth-instar larvae, in which induction was much higher than that in 1- and 2-day-old sixth-instar larvae. To our knowledge, this is the first JHA-inducible GST to have been identified, and we believe that it will provide new insight into the role of GST in insect development, particularly during metamorphosis.