Ectopic expression of a rice triketone dioxygenase gene confers mesotrione tolerance in soybean

Abstract

BACKGROUND: Herbicide-resistant weeds pose a challenge to agriculture and food production. New herbicide tolerance traits in crops will provide farmers with more options to effectively manage weeds. Mesotrione, a selective pre-and post-emergent triketone herbicide used in corn production, controls broadleaf and some annual grass weeds via hydroxyphenylpyruvate dioxygenase (HPPD) inhibition. Recently, the rice HIS1 gene, responsible for native tolerance to the selective triketone herbicide benzobicyclon, was identified. Expression of HIS1 also confers a modest level of mesotrione resistance in rice. Here we report the use of the HIS1 gene to develop a mesotrione tolerance trait in soybean.RESULTS: Conventional soybean is highly sensitive to mesotrione. Ectopic expression of a codon-optimized version of the rice HIS1 gene (TDO) in soybean confers a commercial level of mesotrione tolerance. In TDO transgenic soybean plants, mesotrione is rapidly and locally oxidized into noninhibitory metabolites in leaf tissues directly exposed to the herbicide. These metabolites are further converted into compounds similar to known classes of plant secondary metabolites. This rapid metabolism prevents movement of mesotrione from treated leaves into vulnerable emerging leaves. Minimizing the accumulation of the herbicide in vulnerable emerging leaves protects the function of HPPD and carotenoid biosynthesis more generally while providing tolerance to mesotrione.CONCLUSIONS: Mesotrione has a favorable environmental and toxicological profile. The TDO-mediated soybean mesotrione tolerance trait described here provides farmers with a new option to effectively manage difficult-to-control weeds using familiar herbicide chemistry. This trait can also be adapted to other mesotrione-sensitive crops (e.g. cotton) for effective weed management.

Metabolism of the 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor, Mesotrione, in Multiple-Herbicide-Resistant Palmer amaranth (Amaranthus palmeri)

“…For example, non-P450 Phase I genes and enzymes are associated with tolerance to HPPD inhibitors in rice (Oryza sativa L.); the rice HPPD INHIBITOR SENSITIVE 1 (HIS1) gene encodes an Fe­(II)/2-oxoglutarate-dependent oxygenase that catalyzes detoxification of β-triketone HPPD-inhibiting herbicides . The HIS1 gene also conferred resistance to mesotrione in transgenic soybean . Furthermore, in wild radish (Raphanus raphanistrum), a 2-oxoglutarate/Fe­(II)-dependent dioxygenase ( Rr2ODD1 ), in addition to two P450 genes, confers resistance to HPPD-inhibiting herbicides mesotrione, tembotrione and isoxaflutole …”

“…32,34,35,55 More recently, LCMS-based analysis of mesotrione metabolism in transgenic soybean with ectopic expression of rice HIS1 reported several metabolites, including 4-OH-and 5-OH-mesotrione; however, their experimental mass spectral fragment ions were not presented. 57 This previous study on mesotrione metabolism in transgenic soybean quantified 5-OH-mesotrione in greater abundance compared to 4-OH-mesotrione, which was only detected in control plants. 57 Mesotrione identified in plant extracts had a retention time of approximately 17.4 min and was detected in both ESI(+) and ESI(−) (Table 2).…”

“…57 This previous study on mesotrione metabolism in transgenic soybean quantified 5-OH-mesotrione in greater abundance compared to 4-OH-mesotrione, which was only detected in control plants. 57 Mesotrione identified in plant extracts had a retention time of approximately 17.4 min and was detected in both ESI(+) and ESI(−) (Table 2). In Given these distinct MS2 fragment ions and the hypothesized differential metabolism of mesotrione in Palmer amaranth and waterhemp, the detection of metabolites via LCMS and evaluation of relative metabolite abundance in each population were conducted.…”

“…Although P450s are plausible enzymes associated with Phase I hydroxylation of mesotrione, differences in the abundance of 4-OH-and 5-OH- 65 The HIS1 gene also conferred resistance to mesotrione in transgenic soybean. 57 Furthermore, in wild radish (Raphanus raphanistrum), a 2-oxoglutarate/ Fe(II)-dependent dioxygenase (Rr2ODD1), in addition to two P450 genes, confers resistance to HPPD-inhibiting herbicides mesotrione, tembotrione and isoxaflutole. 28 Rapid metabolic detoxification of mesotrione is a major NTSR mechanism in the Palmer amaranth populations (SYNR1 and SYNR2) investigated in this study.…”

“…However, the functional significance of 4-OH-vs 5-OH-mesotrione metabolites in terms of potential phytotoxicity and overall detoxification processes remains to be determined. 57 3.3.2. Untargeted Metabolite Profiling of Mesotrione Metabolites in Palmer amaranth.…”