Search

Fenquinotrione is a novel herbicide that can control a wide range of broadleaf and sedge weeds with excellent rice selectivity. We revealed that fenquinotrione potently inhibited the 4-hydroxyphenylpyruvate dioxygenase (HPPD) activity in Arabidopsis thaliana with an IC(50) of 44.7 nM. The docking study suggested that the 1,3-diketone moiety of fenquinotrione formed a bidentate interaction with Fe(II) at the active site. Furthermore, π–π stacking interactions occurred between the oxoquinoxaline ring and the conserved Phe409 and Phe452 rings, indicating that fenquinotrione competes with the substrate, similar to existing HPPD inhibitors. A more than 16-fold difference in the herbicidal activity of fenquinotrione in rice and the sedge, Schoenoplectus juncoides, was observed. However, fenquinotrione showed high inhibitory activity against rice HPPD. Comparative metabolism study suggested that the potent demethylating metabolism followed by glucose conjugation in rice was responsible for the selectivity of fenquinotrione.

Fenoxasulfone is a novel rice herbicide that was discovered and developed by Kumiai Chemical Industry Co., Ltd. It displays excellent herbicidal activity against Echinochloa spp. and other annual weeds at 150-200 g a.i./ha with long residual activity and has a favorable toxicological, ecotoxicological, and environmental profile. Fenoxasulfone's mode of action was investigated, and it has been shown to inhibit the biosynthesis of very-long-chain fatty acids in plants. Fenoxasulfone was registered in Japan in 2014, and various products containing fenoxasulfone have been launched. With its high efficacy and long residual activity, we believe that fenoxasulfone will contribute to efficient food production in the future.

The action mechanism of fenoxasulfone was studied by examining the inhibitory effects of this herbicide on the biosynthesis of very-long-chain fatty acids (VLCFAs). Fenoxasulfone treatment decreased VLCFAs, such as C20:0, C20:1, C22:0, C24:0, C24:1 and C26:0 fatty acids, in barnyard millet cultured cells, and increased long-chain-fatty acids and medium-chain-fatty acids, such as C18:0 and C15:0, which are precursors of VLCFAs. Fenoxasulfone potently inhibited activities of VLCFA elongase (VLCFAE) in the microsomal fraction of etiolated barnyard millet seedlings, which catalyzed the elongation steps from C22:0 to C24:0 and C24:0 to C26:0, respectively. These results strongly suggested that fenoxasulfone is a potent inhibitor of plant VLCFAEs and should be categorized within the K3 group of the Herbicide Resistance Action Committee. VLCFAE activity of recombinant Fatty Acid Elongation 1 (FAE1) of Arabidopsis that catalyzes the elongation step from C18:1 to C20:1, was inhibited by fenoxasulfone in a time-dependent manner, which has been shown in the inhibition of VLCFAEs by other well-known VLCFAE-inhibiting herbicides. On the other hand, VLCFAE activity of the microsomal fraction of etiolated barnyard millet seedlings, which catalyzes the elongation step from C24:0 to C26:0, was inhibited by fenoxasulfone in a time-independent manner. This time-independent inhibition raised a new inhibition mechanism of VLCFAE by fenoxasulfone likely with pyroxasulfone, which is classified in the same chemical class as fenoxasulfone.

Pyroxasulfone has been shown to be a potent inhibitor of very-long-chain fatty acid elongase (VLCFAE) of plants; therefore, it is categorized within the K3 group of herbicides. In this paper, we studied the properties of pyroxasulfone as a VLCFAE inhibitor in more detail by examination of its inhibitory effects on VLCFAEs from some plants. Pyroxasulfone inhibited microsomal VLCFAE activities of rice, Italian ryegrass, barnyard millet, wheat, corn and soybean with time-independent reversible inhibition. There were differences in the inhibitory potencies against VLCFAEs between pyroxasulfone-susceptible plants (rice, Italian ryegrass and barnyard millet) and pyroxasulfone-tolerant plants (wheat, corn and soybean). This result confirmed that the difference in the sensitivities of VLCFAEs to pyroxasulfone was one of the factors involved in the selectivity of pyroxasulfone between crops and weeds. We succeeded in preparing recombinant VLCFAEs of Arabidopsis (FAE1) and rice (Q6F365) using yeast and rice cultured cells and constructed each assay system. VLCFAE activities of FAE1 and Q6F365 were potently inhibited by pyroxasulfone; however, a critical difference was found in the inhibition manner between FAE1 and Q6F365. Pyroxasulfone inhibited FAE1 in a time-dependent manner, whereas it inhibited Q6F365 in a time-independent manner. The time-independent reversible inhibition of rice Q6F365 and microsomal VLCFAEs of plants proposes a new inhibition mechanism of VLCFAEs by 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.

Coenzyme Q (CoQ), also called ubiquinone, is an electron transfer molecule in the respiratory chain; it is also a lipid-soluble antioxidant. Most cereal crops produce mainly CoQ9, which has nine isoprene units, whereas humans produce mainly CoQ10, with 10 isoprene units. CoQ10 is a very popular food supplement. Using the cultivar Nipponbare, we previously produced CoQ10-enriched rice plants (Nipponbare-type CoQ10-enriched rice plants) by introduction of the gene for decaprenyl diphosphate synthase (DdsA). In Nipponbare-type CoQ10-enriched rice plants, seed CoQ10 content per weight was increased to up to 10 times that of wild-type rice. However, seed CoQ10 level of those rice plants is still insufficient for practical use, and further 10-times increase in CoQ10 content have been expected. Here, we confirmed preferential accumulation of CoQ in bran and germ of rice seed, and produced improved CoQ10-enriched rice plants by using 2 kinds of giant embryo rice lines, Haiibuki and Chukei-toku 70 (Toku 70). In giant embryo line-type CoQ10-enriched rice plants, seed CoQ10 content per weight was increased to up to 1.4 times (Haiibuki-type) or 1.8 times (Toku 70-type) that in Nipponbare-type CoQ10-enriched rice plants, demonstrating that use of giant embryo rice lines is effective to increase seed CoQ10 content per weight.