Transgenic rice expressing the cry2AX1 gene confers resistance to multiple lepidopteran pests

Abstract

A chimeric Bacillus thuringiensis toxin (Bt) gene, cry2AX1was cloned in a bi-selectable marker free binary vector construct. The cry2AX1 gene, driven by the Chrysanthemum rbcS1 promoter, was introduced into JK1044R, the restorer line (Oryza sativa L. ssp. Indica) of a notified commercially grown rice hybrid in India, by Agrobacterium-mediated transformation. Its effect against two major lepidopteran insect pests viz., yellow stem borer (YSB) Scirpophaga incertulas, rice leaf folder (RLF) Cnaphalocrocis medinalis and one minor insect pest, oriental army worm (OAW) Mythimna separata was demonstrated through bioassays of transgenic rice plants under laboratory and greenhouse conditions. The rbcS1 promoter with chloroplast signal peptide was used to avoid Cry2AX1 protein expression in rice seed endosperm tissue. A total of 37 independent transformants were generated, of which after preliminary molecular characterization and YSB bioassay screening, five events were selected for their protein expression and bioefficacy against all three rice insect. One elite transgenic rice line, BtE15, was identified with Cry2AX1 expression ranging from 0.68 to 1.34 µg g(-1) leaf fresh weight and with 80-92 % levels of resistance against rice pests at the vegetative and reproductive stages. Increase in Cry2AX1 protein concentration was also observed with crop maturity. The Cry2AX1protein concentration in the de-husked seeds was negligible (as low as 2.7-3.6 ng g(-1)). These results indicate the potential application of cry2AX1 gene in rice for protection against YSB, RLF and OAW.

Strategies for Enhanced Crop Resistance to Insect Pests

“…Genetic technologies are enhancing the efficacy of Bt toxins. Domains from different Bt toxins have been recombined to enhance efficacy; e.g., Cry2AX1 (a fusion product of Cry2Aa and Cry2Ac) protects against multiple lepidopterans (23). Bt toxins have also been engineered to confer activity against hemipteran pests, which are not susceptible to most naturally occurring Bt toxins (97).…”

Assessment of Pigeonpea (Cajanus cajan L.) transgenics expressing Bt ICPs, Cry2Aa and Cry1AcF under nethouse containment implicated an effective control against herbivory by Helicoverpa armigera (Hübner)

“…Since the 1990s, this strategic biotechnological approach has been increasingly adopted in many parts of the world, especially for corn and cotton pest management. The utility of Bt ICPs in conferring resistance to varied pests has been demonstrated in a wide range of crops . In pigeonpea, major crop losses resulting in stagnated productivity are mainly due to various biotic and abiotic factors, including herbivory by H. armigera .…”

“…The utility of Bt ICPs in conferring resistance to varied pests has been demonstrated in a wide range of crops. [39][40][41][42][43] In pigeonpea, major crop losses resulting in stagnated productivity are mainly due to various biotic and abiotic factors, 1,2,44 including herbivory by H. armigera. 45,46 A major impetus for the mitigation of this pest in pigeonpea has been transgenesis due to the lack of availability of resistance sources in the cultivated germplasm.…”

Current understanding of the genomic, genetic, and molecular control of insect resistance in rice

“…Bt genes are highly effective against chewing insects in rice, making them ideal targets for the control of SSB and RLF. For example, transgenic rice expressing the Bt gene cry2AX1 exhibited increased resistance to multiple lepidopteran pests (Chakraborty et al 2016). However, several pests have recently developed resistance to overcome Bt crops in the field (Tabashnik et al 2013).…”