AUTHOR=Karthik Kesiraju , Negi Jyotsana , Rathinam Maniraj , Saini Navinder , Sreevathsa Rohini 

TITLE=Exploitation of Novel Bt ICPs for the Management of Helicoverpa armigera (Hübner) in Cotton (Gossypium hirsutum L.): A Transgenic Approach

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.661212

DOI=10.3389/fmicb.2021.661212

ISSN=1664-302X

ABSTRACT=<p>Cotton is a commercial crop of global importance. The major threat challenging the productivity in cotton has been the lepidopteron insect pest <italic>Helicoverpa armigera</italic> or cotton bollworm which voraciously feeds on various plant parts. Biotechnological interventions to manage this herbivore have been a universally inevitable option. The advent of plant genetic engineering and exploitation of <italic>Bacillus thuringiensis</italic> (<italic>Bt</italic>) insecticidal crystal proteins (ICPs) marked the beginning of plant protection in cotton through transgenic technology. Despite phenomenal success and widespread acceptance, the fear of resistance development in insects has been a perennial concern. To address this issue, alternate strategies like introgression of a combination of cry protein genes and protein-engineered chimeric toxin genes came into practice. The utility of chimeric toxins produced by domain swapping, rearrangement of domains, and other strategies aid in toxins emerging with broad spectrum efficacy that facilitate the avoidance of resistance in insects toward cry toxins. The present study demonstrates the utility of two <italic>Bt</italic> ICPs, <italic>cry1AcF</italic> (produced by domain swapping) and <italic>cry2Aa</italic> (produced by codon modification) in transgenic cotton for the mitigation of <italic>H. armigera.</italic> Transgenics were developed in cotton cv. Pusa 8–6 by the exploitation of an apical meristem-targeted <italic>in planta</italic> transformation protocol. Stringent trait efficacy-based selective screening of T<sub>1</sub> and T<sub>2</sub> generation transgenic plants enabled the identification of plants resistant to <italic>H. armigera</italic> upon deliberate challenging. Evaluation of shortlisted events in T<sub>3</sub> generation identified a total of nine superior transgenic events with both the genes (six with <italic>cry1AcF</italic> and three with <italic>cry2Aa</italic>). The transgenic plants depicted 80–100% larval mortality of <italic>H. armigera</italic> and 10–30% leaf damage. Molecular characterization of the shortlisted transgenics demonstrated stable integration, inheritance and expression of transgenes. The study is the first of its kind to utilise a non-tissue culture-based transformation strategy for the development of stable transgenics in cotton harbouring two novel genes, <italic>cry1AcF</italic> and <italic>cry2Aa</italic> for insect resistance. The identified transgenic events can be potential options toward the exploitation of unique <italic>cry</italic> genes for the management of the polyphagous insect pest <italic>H. armigera</italic>.</p>