Characterization of Cytochrome P450s with Key Roles in Determining Herbicide Selectivity in Maize

Abstract

Safeners such as metcamifen and benoxacor are widely used in maize to enhance the selectivity of herbicides through the induction of key detoxifying enzymes, notably cytochrome P450 monooxygenases (CYPs). Using a combination of transcriptomics, proteomics, and functional assays, the safener-inducible CYPs responsible for herbicide metabolism in this globally important crop have been identified. A total of 18 CYPs belonging to clans 71, 72, 74, and 86 were safener-induced, with the respective enzymes expressed in yeast and screened for activity toward thiadiazine (bentazon), sulfonylurea (nicosulfuron), and triketone (mesotrione and tembotrione) chemistries. Herbicide metabolism was largely restricted to family CYP81A members from clan 71, notably CYP81A9, CYP81A16, and CYP81A2. Quantitative transcriptomics and proteomics showed that CYP81A9/CYP81A16 were dominant enzymes in safener-treated field maize, whereas only CYP81A9 was determined in sweet corn. The relationship between CYP81A sequence and activities were investigated by splicing CYP81A2 and CP81A9 together as a series of recombinant chimeras. CYP81A9 showed wide ranging activities toward the three herbicide chemistries, while CYP81A2 uniquely hydroxylated bentazon in multiple positions. The plasticity in substrate specificity of CYP81A9 toward multiple herbicides resided in the second quartile of its N terminal half. Further phylogenetic analysis of CYP81A9 showed that the maize enzyme was related to other CYP81As linked to agrochemical metabolism in cereals and wild grasses, suggesting this clan 71 CYP has a unique function in determining herbicide selectivity in arable crops.

Rapid metabolism and increased expression of CYP81E8 gene confer high level of resistance to tembotrione in a multiple-resistant Palmer amaranth (Amaranthus palmeri S. Watson)

“…Our data suggest that no changes in tembotrione absorption or translocation that could confer resistance in KCTR (Figure 2). Triketone herbicides are widely used for weed control in corn as it can rapidly metabolize this herbicide into more polar and less toxic metabolites because of Phase I hydroxylation and dealkylation mediated by CYP activity (Brazier-hicks et al, 2022). In this research, the metabolic profiles of tembotrione showed presence of metabolites M1 and M3 in corn (Figures 3G, H), whereas in Palmer amaranth, M1 and M2 were identified as major metabolites at 6 HAT (Figures 3A, 3C).…”

“…Nsf1/Ben1 (gene named for nicosulfuron, Nsf, and bentazon, Ben) identified as the single major locus in corn which corresponded to CYP81A9 was implicated in resistance to nicosulfuron, a sulfonylurea herbicide (Williams and Pataky, 2008;Choe and Williams, 2020). Hitherto, few herbicides metabolizing CYPs have been expressed in heterologous system and characterized in plants (Dimaano et al, 2020;Brazier-hicks et al, 2022). CYP81A9 of corn that was found to metabolize multiple herbicides, including mesotrione, tembotrione and sulcotrione through the oxidation of cyclohexanedione ring (Brazier-hicks et al, 2022).…”

“…Hitherto, few herbicides metabolizing CYPs have been expressed in heterologous system and characterized in plants (Dimaano et al, 2020;Brazier-hicks et al, 2022). CYP81A9 of corn that was found to metabolize multiple herbicides, including mesotrione, tembotrione and sulcotrione through the oxidation of cyclohexanedione ring (Brazier-hicks et al, 2022). Previous research identified the specific CYP isoforms that are differentially expressed in herbicide-resistant and -susceptible plants were found responsible for metabolism of the herbicides (Giacomini et al, 2020;Han et al, 2021).…”

“…CYP81 family of enzymes has been identified to metabolize diverse herbicides in corn and weed species such as rigid ryegrass (Lolium rigidum) and late watergrass (Echinochloa phyllopogon) (Dimaano et al, 2020;Dimaano and Iwakami, 2021;Han et al, 2021). CYP81A9 and CYP81A10v7 genes are involved in conferring resistance to mesotrione in corn and rigid ryegrass, respectively (Han et al, 2021;Brazier-hicks et al, 2022).…”

Genetic diversity of North American popcorn germplasm and the effect of population structure on nicosulfuron response

“…Although CYP72A27 is a cytochrome p450, its identification here is somewhat unexpected, as it belongs to the CYP clan 72 group of cytochrome p450s. Members of this clan are generally associated with secondary metabolism, while clan 71 enzymes, such as CYP81A9 , are responsible for herbicide detoxification (Prall et al 2016; Brazier-Hicks et al 2022). However, sulfonylurea herbicide metabolism via clan 72 enzymes has been shown in other crops, such as CYP72A31 in Oryza indica (Saika et al 2014) and CYP749A16 in Gossypium hirsutum (Thyssen et al 2018).…”