Bt corn is one of the top three large-scale commercialized transgenic crops around the world. It is increasingly clear that the complementary durable approaches for pest control, which combine the endogenous defense of the crop with the introduced foreign genes, are promising alternative strategies for pest resistance management and the next generation of insect-resistant transgenic crops. In the present study, we tested the inducible effects of exogenous jasmonic acid (JA) on direct-defense chemical content, Bt protein concentration, and related gene expression in the leaves of Bt corn cultivar 34B24 and non-Bt cultivar 34B23 by chemical analysis, ELISA, and RT-PCR. The results show that the expression of LOX, PR-2α, MPI, and PR-1 genes in the treated leaf (the first leaf) was promoted by exogenous JA both in 34B24 and 34B23. As compared with the control, the concentration of DIMBOA in the treated leaf was significantly increased by 63 and 18% for 34B24 and 34B23, respectively. The total phenolic acid was also increased by 24 and 12% for both 34B24 and 34B23. The Bt protein content of 34B24 in the treated leaf was increased by 13% but decreased significantly by 27% in the second leaf. The induced response of 34B24 was in a systemic way and was much stronger than that of 34B23. Those findings indicated that there is a synergistic interaction between Bt gene and internally induced chemical defense system triggered by externally applied JA in Bt corn.
