Abstract：Induced defense plays a key role in plant resistance against herbivores, and mediate interactions between phytophagous arthropods and plants via genes and signal pathways. The objective of this study is to understand the role of Ghppo1 gene in induced defense and cotton-cotton bollworm interaction in Bt cotton with Bt+CpTI (Bacillus thuringiensis+cowpea trypsin inhibitor) genes. Using the qRT-PCR, the expression changes of the Ghppo1 (gossypium hirsutum polyphenol oxidases 1 gene), jasmonic acid signaling pathway genes of cotton (Gossypium hirsutum) (i.e., gossypium hirsutum allene oxide synthase, GhAOS and gossypium hirsutum coronatine insensitive1, GhCOI1), which were damaged by Helicoverpa armigera and sprayed with Me-JA and Me-SA for 0, 6, 12, 18 and 24 h, respectively, were studied. The weight changes of Helicoverpa armigera and Spodoptera exigua which were fed on cotton plants that treated with first star H. armigera and Me-JA. Ghppo1 expression was up-regulated by infestations of first instar H. armigera larvae and applications of methyl jasmonate (Me-JA). In contrast, the third instar larvae and methyl salicylate (Me-SA) did not increase Ghppo1 expression levels in cotton plants. Additionally, cotton polyphenol oxidase activities were also up-regulated by first instar H. armigera larvae and Me-JA, but not by third instar larvae or Me-SA. The expression of GhAOS and GhCOI1 was induced by infestation of first instar H. armigera larvae. Infestations of H. armigera on cotton revealed that plants previously treated with first instar H. armigera larvae exhibit significantly increased resistance than third instar H. armigera and S. exigua. Ghppo1 expression was mediated by jasmonic acid, but not salicylic acid signaling pathway, and may be involved in this interaction among insect herbivores and cotton defense responses. This study shows that the first instar H. armigera larvae can induce resistance against H. armigera and S. exigua by regulating Ghppo1 expression levels.
