Cypyrafluone, a 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor to Control Weed in Wheat Fields

As a bleaching herbicide, cypyrafluone was applied postemergencein wheat fields for annual weed control; especially, this herbicidepossesses high efficacy against cool-season grass weed species suchas Alopecurus aequalis and Alopecurus japonicus. In this study, the target ofaction of cypyrafluone on 4-hydroxyphenylpyruvate dioxygenase (HPPD)inhibition was confirmed. This herbicide caused severe foliar whiteningsymptoms at 5-7 days after treatment (DAT) and death of thewhole plant within 10 DAT. Significant increases in phytoene contentand significant decreases in kinds of carotenoid and chlorophyll pigmentswere observed. The content of chlorophyll pigments in cypyrafluone-treated Spirodela polyrhiza decreased upon the addition ofhomogentisic acid (HGA), which indicated that cypyrafluone preventsthe HGA production, possibly by inhibiting the catalytic activityof 4-HPPD. Indeed, cypyrafluone strongly inhibited the catalytic activityof Arabidopsis thaliana HPPD producedby Escherichia coli, which was approximately2 times less effective than mesotrione. In addition, overexpressionof Oryza sativa HPPD in rice and A. thaliana both conferreda high tolerance level to cypyrafluone on them. Molecular dockingfound that cypyrafluone bonded well to the active site of the HPPDand formed a bidentate coordination interaction with the Fe2+ atom, with distances of 2.6 and 2.7 angstrom between oxygen atomsand the Fe2+ atom and a binding energy of -8.0 kcalmol(-1).

Automated summary

This study confirmed the inhibitory effect of cypyrafluone on 4-hydroxyphenylpyruvate dioxygenase (HPPD). Cypyrafluone caused severe foliar whitening symptoms and plant death within a short period of time. It was found that cypyrafluone decreases the content of chlorophyll pigments and inhibits the catalytic activity of 4-HPPD. Molecular docking analysis showed that cypyrafluone binds well to the active site of HPPD and forms a bidentate coordination interaction with the Fe2+ atom.