Development of insect resistant transgenic cotton lines expressing cry1EC gene from an insect bite and wound inducible promoter

Abstract

Transgenic cotton lines were developed for high-level expression of a synthetic cry1EC gene from a wound inducible promoter. The tobacco pathogenesis related promoter PR-1a was modified by placing CaMV35S promoter on its upstream in reverse orientation. The resultant chimeric promoter CaMV35S(r)PR-1a expressed constitutively and was further up-regulated at the site of feeding by insects. It was induced more rapidly by treatment with salicylic acid (SA). The CaMV35S(r)PR-1a cry1EC expressing transgenic lines of cotton showed 100% mortality of Spodoptera litura larvae. The tightly regulated low-level expression of PR-1a was modified to a highly expressing constitutive expression by CaMV35S placed in reverse orientation. Salicylic acid treatment and wounding enhanced the expression further by the chimeric promoter. The leaves expressed more δ-endotoxin around the sites of insect bites. The levels of expression and induction varied among different transgenic lines, suggesting position effect. Some of the transgenic lines that expressed Cry1EC from the chimeric promoter at a low level also showed 100% mortality when induced with salicylic acid. A highly expressing insect bite and wound inducible promoter is desirable for developing insect resistant transgenic plants.