Discovery of Anti-Bt-Vip3A Gene

Yutao Xiao's team at the Chinese Academy of Agricultural Sciences and their collaborators published a research paper titled "Downregulation of a transcription factor associated with resistance to Bt toxin Vip3Aa in the invasive fall armyworm" in PNAS. This study comprehensively used genetics, molecular biology, gene editing and other research methods to locate the first Bt-Vip3A resistance gene. The resistance gene is a myb transcription factor (named Sfmyb). Further research found that deletion of the Sfmyb promoter region resulted in a significant down-regulation of its expression, mediating the resistance of Spodoptera frugiperda to the new insecticidal protein Vip3Aa. This study identified the Bt-Vip3A resistance gene locus for the first time in the world and analyzed the mechanism of action of the candidate gene.

Vegetative insecticidal proteins (Vip3A) are a new type of insecticidal protein produced by Bacillus thuringiensis (Bt) during the vegetative growth stage and have strong insecticidal activity against many important lepidopteran pests. It is an extremely important tool gene for biological breeding. Corn and cotton crops expressing Vip3A have been commercially grown in the United States, Brazil, Argentina and other places, playing an important role in ensuring food security production. However, research on the mechanism of action and resistance mechanism of Vip3A protein is still very scarce, which is a major hidden danger for the continued effectiveness of insect-resistant crops.

Using S. frugiperda, a major invasive agricultural pest, as a model, the author obtained a line DH-R with 206 times resistance to Vip3Aa through 35 generations of selection. A GWAS analysis was carried out using the phenotype of F2 isolates, and a candidate interval was successfully located through forward genetics. Subsequently, through fine mapping and transcriptome analysis between resistance and susceptibility, a resistance-related gene Sfmyb was identified. Further using a reverse genetic strategy based on CRISPR/Cas9 gene editing and RNAi, after knocking out or knocking down this gene in S. frugiperda, the larvae's sensitivity to Vip3Aa was significantly reduced, thus confirming that Sfmyb is the key gene for S. frugiperda's resistance to Vip3Aa. The promoter region was cloned and it was found that the Sfmyb promoter in the resistant strain had multiple point mutations and 2 indels. The promoter activity experiment showed that the Sfmyb promoter activity was significantly down-regulated in the resistant strain. Finally, the yeast one-hybrid system was used to predict the downstream target genes regulated by Sfmyb, and the potential target genes were analyzed.

For the first time, the study located the key gene responsible for resistance to Vip3 proteins and revealed its mechanism of action. This result provides important support for ensuring the sustainable cultivation of Bt insect-resistant crops in the future.

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Reference:

Jin, M., et al. Downregulation of a transcription factor associated with resistance to Bt toxin Vip3Aa in the invasive fall armyworm. Proc Natl Acad Sci U S A. 2023, 120(44): e2306932120.

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