Flusulfinam, a novel amide herbicide to control weed in rice fields, targets 4-hydroxyphenylpyruvate dioxygenase

Flusulfinam, a post-emergence (POST)-applied herbicide in rice fields to manage annual weeds, has been proven to be safe for various rice strains of japonica and indica. The study confirmed its mechanism of action by inhibiting 4-hydroxyphenylpyruvate dioxygenase (HPPD). The POST application of flusulfinam led to noticeably bleaching symptom in leaves of Echinochloa crus-galli within 3 to 7 days and plant mortality by 10 days. In Echinochloa crus-galli, flusulfinam induced a significant rise in level of phytoene content, while there was a significant decrease in levels of carotenoid and chlorophyll contents. Meanwhile, the increase in levels of chlorophyll content in Spirodela polyrrhiza treated with flusulfinam after homogentisic acid (HGA) addition was observed, suggesting that flusulfinam inhibited HGA production, likely by suppressing HPPD activity. Flusulfinam significantly diminished the catalytic activity of recombinant Arabidopsis thaliana HPPD that was expressed by Escherichia coli, exhibiting an inhibitory efficacy approximately 16-fold higher than the HPPD-inhibiting mesotrione. Additionally, the rice with overexpression of Oryza sativa HPPD showed higher tolerance to flusulfinam than rice of wild type. Furthermore, molecular docking analyses revealed that flusulfinam formed effective bonds with the HPPD active site via the nitrogen atom of the oxadiazole ring and the oxygen atom of the amide group, with distances of 2.0 Å and 2.4 Årespectively, which engaged in bidentate coordination with the Fe²⁺ ion, with a binding energy of -8.7 kcal mol^-1, and HPPD-flusulfinam complex showed low root-mean square deviation values of less than 2 Å in molecular dynamics tests. This study provides the first evidence of the molecular targets of flusulfinam.