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 tr uncated cry1Ac9 to produce cry1Ac9(A) (one nucleotide change) and then cry1 Ac9(B) (seven nucleotide changes). The derivative genes under the control o f the CaMV 35S promoter were transformed into Nicotiana tabacum in order to determine whether these modified genes conferred resistance on the resulti ng transgenic tobacco plants to larvae of the potato tuber moth (Phthorimae a operculella). Over two trials with PTM larvae on the transgenic plants ex pressing the cry1Ac9(B) gene, lower larval growth, development and survival was evident for most of the lines compared to the control plants. In the s econd 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 con trol 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 t he transgenic tobacco lines containing cry1Ac9(B) than in the tobacco lines containing cry1Ac9(A). These results suggest that certain minor modificati ons to the nucleotide sequence of cry1Ac9 are sufficient to improve the sta bility of its mRNA when expressed in tobacco and that this increase in stea dy state mRNA is sufficient to confer significant resistance to PTM larvae.