Action mechanism of a novel herbicide, pyroxasulfone

The mechanism of action of pyroxasulfone was studied by examination of the inhibitory effects of this herbicide on the biosynthesis of very-long-chain fatty acids (VLCFAs) both in vivo and in vitro. Pyroxasulfone treatment drastically reduced the biosynthesis of VLCFAs and caused a buildup of fatty acid precursors in cultured rice cells. Pyroxasulfone specifically inhibited the elongation steps from C18:0 to C20:0, C20:0 to C22:0, C22:0 to C24:0, C24:0 to C26:0 and C26:0 to C28:0, catalyzed by VLCFA elongases (VLCFAEs) in plants including rice. These results suggested that pyroxasulfone is a potent inhibitor of VLCFA biosynthesis, and should be categorized within the K3 group of herbicides. Twenty putative VLCFAEs of rice were identified by blastp search with the amino acid sequences of Arabidopsis VLCFAEs. Oligo microarray and real time RT-PCR analysis revealed that Q5Z6S3 and Q8H7Z0, which were identified by their Uniplot ID number, might play important roles during the biosynthesis of C28:0 and C30:0 VLCFAs in shoot formation, and biosynthesis of C20:1 and C22:1 VLCFAs in cell proliferation, respectively. These VLCFAEs are likely targets for pyroxasulfone.