Metabolic Resistance to Acetolactate Synthase Inhibiting Herbicide Tribenuron-Methyl in Descurainia sophia L. Mediated by Cytochrome P450 Enzymes

Descurainia sophia is one of the most notorious broadleaf weeds in China and has evolved extremely high resistance to acetolactate synthase (ALS)-inhibiting herbicide tribenuron-methyl. The target-site resistance due to ALS gene mutations was well-known, while the non-target-site resistance is not yet well-characterized. Metabolic resistance, which is conferred by enhanced rates of herbicide metabolism, is the most important NTSR. To explore the mechanism of metabolic resistance underlying resistant (R) D. sophia plants, tribenuron-methyl uptake and metabolism levels, qPCR reference gene stability, and candidate P450 genes expression patterns were investigated. The results of liquid chromatography-mass spectrometry (LC-MS) analysis indicated that the metabolic rates of tribenuron-methyl in R plants was significantly faster than in susceptible (S) plants, and this metabolism differences can be eliminated by P450 inhibitor malathion. The genes for 18S rRNA and TIP41-like were identified as the most suitable reference genes using programs of BestKeeper, NormFinder, and geNorm. The P450 gene CYP96A146 constitutively overexpressed in R plants compared to S plants; this overexpression in R plants can be suppressed by malathion. Taken together, a higher expression level of P450 genes, leading to higher tribenuron-methyl metabolism, appears to be responsible for metabolic resistance to tribenuron-methyl in R D. sophia plants.