Cytochrome CYP72A15 may play a role in metabolic resistance to mesotrione in wild radish

In our previous study with a wild radish (Raphanus raphanistrum) population resistant to HPPD-inhibiting herbicides we indicated that two additional candidate P450 genes, CYP71A28 and CYP72A13-like, may also contribute to the resistance. This study investigates the role of these two P450 genes in mesotrione resistance in the wild radish population. The full-length R. raphanistrum P450 genes (thereafter named as RrCYP71A28 and RrCYP72A15) were cloned from mesotrione-resistant (R) and -susceptible (S) wild radish plants. RT-qPCR results showed that basal expression levels of the two P450 genes are significantly higher (up to 3-fold) in the R than the S plants. Escherichia coli cells transformed respectively with RrCYP71A28 and RrCYP72A15 were more tolerant to mesotrione. Transgenic Arabidopsis plants expressing RrCYP72A15 showed a modest level of resistance to mesotrione. UPLC-MS/MS analysis demonstrated that tissue mesotrione levels in RrCYP72A15 transgenic Arabidopsis plants were significantly lower (up to 2-fold) than that in the wild type. Structural modelling predicts CYP72A15 can bind to RrCYP72A15 and metabolize mesotrione likely through formation of 4-OH-mesotrione. Although the RrCYP72A15 gene confers a modest level of resistance, overexpression of the multiple herbicide-metabolizing genes could contribute to the low level of mesotrione resistance observed in the R wild radish population.