Downregulation of a transcription factor associated with resistance to Bt toxin Vip3Aa in the invasive fall armyworm

Abstract

Transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt) have revolutionized control of some major pests. However, more than 25 cases of field-evolved practical resistance have reduced the efficacy of transgenic crops producing crystalline (Cry) Bt proteins, spurring adoption of alternatives including crops producing the Bt vegetative insecticidal protein Vip3Aa. Although practical resistance to Vip3Aa has not been reported yet, better understanding of the genetic basis of resistance to Vip3Aa is urgently needed to proactively monitor, delay, and counter pest resistance. This is especially important for fall armyworm ( Spodoptera frugiperda ), which has evolved practical resistance to Cry proteins and is one of the world’s most damaging pests. Here, we report the identification of an association between downregulation of the transcription factor gene SfMyb and resistance to Vip3Aa in S. frugiperda . Results from a genome-wide association study, fine-scale mapping, and RNA-Seq identified this gene as a compelling candidate for contributing to the 206-fold resistance to Vip3Aa in a laboratory-selected strain. Experimental reduction of SfMyb expression in a susceptible strain using RNA interference (RNAi) or CRISPR/Cas9 gene editing decreased susceptibility to Vip3Aa, confirming that reduced expression of this gene can cause resistance to Vip3Aa. Relative to the wild-type promoter for SfMyb , the promoter in the resistant strain has deletions and lower activity. Data from yeast one-hybrid assays, genomics, RNA-Seq, RNAi, and proteomics identified genes that are strong candidates for mediating the effects of SfMyb on Vip3Aa resistance. The results reported here may facilitate progress in understanding and managing pest resistance to Vip3Aa.

Retrotransposon-mediated variation of a chitin synthase gene confers insect resistance toBacillus thuringiensisVip3Aa toxin

“…Furthermore, knockout of either SR-C or FGFR via CRISPR/Cas9 does not cause significant susceptibility alteration in S. frugiperda (35). The downregulation of SfMyb causes just 206-fold resistance to Vip3Aa in a laboratory-selected strain, in which the transcripts of SfCHS2 have not been affected (31). However, in this study, knockout of SfCHS2 in S. frugiperda was demonstrated to confer complete resistance to Vip3Aa toxin.…”

“…Recently, downregulation of a transcription factor, SfMyb, was reported to be associated with resistance to Vip3Aa in S. frugiperda (31). However, the variation of SfMyb can causes just 206fold resistance to Vip3Aa in S. frugiperda.…”

Diverse genetic basis of Vip3Aa resistance in five independent field‐derived strains of Helicoverpa zea in the US

“…However, this degree of dominance in S . frugiperda calculated by Jin et al 46 . was based on a Vip3Aa concentration of 0.4 μg cm −2 , which is lower than the concentration typically produced by Bt corn and cotton plants 47–50 .…”

“…also reported that a laboratory‐selected Vip3Aa resistant strain of S . frugiperda in China showed autosomal and partially recessive resistance with a degree of dominance, h , of 0.13 ( h = 0 indicates completely recessive resistance, h = 1 indicates completely dominant resistance) 46 . However, this degree of dominance in S .…”

Susceptibility of Fall Armyworm Field Populations to Vip3Aa/Cry Bt Maize in a Tropical Agricultural Region

“…This may have contributed to the high Bt susceptibility of FAW larvae in our study. In addition, inducible resistance to Vip3Aa [48] is yet to be tested in field-selected FAW populations. We showed that the Vip3Aa and Cry proteins produced in Bt maize hybrids remain effective at killing third-instar F 1 FAWs descendants from the larvae collected in the fields described here.…”