Expression of GNA and biting site-restricted cry1Ac in cotton; an efficient attribution to insect pest management strategies

Insect-resistant transgenic cotton has been commercialized for two decades. Most of the introduced cultivars express Bt gene(s) constitutively under the control of 35S promoter in whole-plant tissues. However, there have been other promoters considered by researchers to confine the toxin expression to targeted organ and tissues. We developed a triple-gene construct including GNA, cry1Ac and cp4 epsps genes. We attempted to confine cry1Ac expression to insect biting sites by cloning it to downstream of a wound-inducible promoter isolated from Asparagus officinalis (AoPR1). Moreover, to broaden the range of resistance, GNA was driven by the 35S promoter to target the sap-sucking insects like aphids which impose large losses in cotton production. To select the transformants in selection medium and for glyphosate tolerance, GNA and cry1Ac genes were accompanied with cp4 epsps gene. Two binary vectors harboring desired genes were constructed and utilized in the study (pGTGNAoC1AC and pGTGN35C1AC). Transformation of cultivar GSN-12 was carried out by employing Agrobacterium tumefaciens strain EHA105. Plantlets were primarily screened under glyphosate (N-phosphonomethyl glycine) selection pressure and subsequently subjected to molecular and biotoxicity assays. Introduction of cry1Ac and GNA to cotton plant conferred resistance to Spodoptera littoralis and Aphis gossypii Glover. Restriction of cry1Ac toxin protein to insect biting sites along with a plant lectin attributes significantly to insect pest management strategies.