Expression of cry1Ac9 and cry9Aa2 genes under a potato light-inducible Lhca3 promoter in transgenic potatoes for tuber moth resistance

Abstract

In transgenic potato it is often desirable to couple high-level expression in foliage with no expression in the edible tubers, especially for resistance to pests that primarily infest foliage. To accomplish this we have investigated the use of a light inducible Lhca3 promoter for transcriptional control of cry1Ac9 and cry9Aa2 genes for resistance to potato tuber moth (PTM) (Phthorimaea operculella). Thirty-five and thirty-one independently derived transgenic lines of potato cultivar Iwa were regenerated for the cry1Ac9 and cry9Aa2 genes respectively. Significantly inhibited larval growth of PTM on excised greenhouse-grown leaves was observed in 51% of the cry1Ac9-trangenic lines and 84% of the cry9Aa2-transgenic lines. RT-PCR analysis identified several transgenic lines with high levels of crygene mRNA in leaves and no to low levels in tubers. Southern and ELISA analyses on eight selected cry1Ac9-transgenic lines revealed that they contained 2 to 9 copies of the cry1Ac9 gene and the amount of Cry protein in leaves was less than 60 ng g−1of fresh leaf tissue. Southern analysis for four selected cry9Aa2-transgenic lines revealed that they contained 2 to 6 copies of the cry9Aa2 gene. This study has established that the expression of either the cry1Ac9 gene or the cry9Aa2 gene in transgenic potato plants offers protection against PTM larval damage in foliage when expressed under the transcriptional control of a Lhca3 light-inducible promoter. Several transgenic lines were identified with high crygene expression, high resistance to PTM larvae in the foliage, and no or minimalcrygene expression in tubers.