F116I mutation in CYP9A25 associated with resistance to emamectin benzoate in Spodoptera litura

BACKGROUND

The F116V mutation in the substrate recognition site 1 (SRS1) of Spodoptera exigua CYP9A186 has been demonstrated to confer ~200-fold resistance to emamectin benzoate (EB). In this study, a novel mutation (F116I) in CYP9A25, orthologous to CYP9A186, was detected in a field population of Spodoptera litura (YJ22) collected from Yuanjiang, Yunnan province, China in 2022. The association of this mutation with EB resistance was investigated.

RESULTS

Two homozygous strains, YJ22-116F (wild-type at 116 position of CYP9A25) and YJ22-116I (mutant) were isolated from YJ22 through two rounds of crossing and DNA genotyping. Compared with YJ22-116F, the mutant strain YJ22-116I exhibited 31.8-fold resistance to EB. Resistance in YJ22-116I was shown to be incompletely dominant, and genetically linked with the F116I mutation. Further, heterologous expression and in vitro metabolism assays confirmed that the recombinant CYP9A25 protein with 116I mutation obtained metabolic capability against EB, whereas the wild-type CYP9A25 protein (with 116F) did not metabolize EB. Molecular modeling showed that the F116I mutation within SRS1 reduces the steric hindrance to substrate entry and improves ligand-binding interactions.

CONCLUSION

The causal association between the F116I mutation in CYP9A25 and medium-level EB resistance in S. litura has been verified. This finding is critical for the field monitoring of such mutations and thus for developing adaptive resistance management tactics for field populations of S. litura. © 2024 Society of Chemical Industry.