Minor modifications to the cry1Ac9 nucleotide sequence are sufficient to generate transgenic plants resistant to Phthorimaea operculella

Minor modifications were made sequentially to the nucleotide sequence of truncated cry1Ac9 to produce cry1Ac9(A) (one nucleotide change) and then cry1Ac9(B) (seven nucleotide changes). The derivative genes under the control of the CaMV 35S promoter were transformed into Nicotiana tabacum in order to determine whether these modified genes conferred resistance on the resulting transgenic tobacco plants to larvae of the potato tuber moth (Phthorimaea operculella). Over two trials with PTM larvae on the transgenic plants expressing the cry1Ac9(B) gene, lower larval growth, development and survival was evident for most of the lines compared to the control plants. In the second trial, for four of these lines (7, 25, 26 and 28) larval growth rates were very low (0.28, 0.3, 0.42 and 0.28, respectively) compared to the control growth rate (4.18) and leaf damage was minimal. Northern analysis and RT-PCR analysis showed that higher levels of cry1Ac9 mRNA were present in the transgenic tobacco lines containing cry1Ac9(B) than in the tobacco lines containing cry1Ac9(A). These results suggest that certain minor modifications to the nucleotide sequence of cry1Ac9 are sufficient to improve the stability of its mRNA when expressed in tobacco and that this increase in steady state mRNA is sufficient to confer significant resistance to PTM larvae.