Establishing a herbicide-metabolizing enzyme library in Beckmannia syzigachne to identify genes associated with metabolic resistance.

Non-target site resistance (NTSR) to herbicides is an increasing concern for weed control. Metabolic herbicide resistance is an important mechanism for NTSR. However, little is known about metabolic resistance at the genetic level. In this study, we have identified three fenoxaprop-P-ethyl-resistant American sloughgrass (Beckmannia syzigachne Steud.) populations, in which the molecular basis for NTSR remains unclear. To reveal the mechanisms of metabolic resistance, the genes likely to be involved in herbicide metabolism (e.g. for cytochrome P450s, esterases, hydrolases, oxidases, peroxidases, glutathione S-transferases, glycosyltransferases, and transporter proteins) were isolated using transcriptome sequencing, in combination with RT-PCR (reverse transcription-PCR) and RACE (rapid amplification of cDNA ends). Consequently, we established a herbicide-metabolizing enzyme library containing at least 332 genes, and each of these genes was cloned and the sequence and the expression level compared between the fenoxaprop-P-ethyl-resistant and susceptible populations. Fifteen metabolic enzyme genes were found to be possibly involved in fenoxaprop-P-ethyl resistance. In addition, we found five metabolizing enzyme genes that have a different gene sequence in plants of susceptible versus resistant B. syzigachne populations. These genes may be major candidates for herbicide metabolic resistance. This established metabolic enzyme library represents an important step forward towards a better understanding of herbicide metabolism and metabolic resistance in this and possibly other closely related weed species. This new information may help to understand weed metabolic resistance and to develop novel strategies of weed management.