Several triazole-containing chemicals have previously been shown to act as efficient inhibitors of cytochrome P450 monooxygenases. To discover a strigolactone biosynthesis inhibitor, we screened a chemical library of triazole derivatives to find chemicals that induce tiller bud outgrowth of rice seedlings. We discovered a triazole-type chemical, TIS13 [2,2-dimethyl-7-phenoxy-4-(1H-1,2,4-triazol-1-yl)heptan-3-ol], which induced outgrowth of second tiller buds of wild-type seedlings, as observed for non-treated strigolactone-deficient d10 mutant seedlings. TIS13 treatment reduced strigolactone levels in both roots and root exudates in a concentration-dependent manner. Co-application of GR24, a synthetic strigolactone, with TIS13 canceled the TIS13-induced tiller bud outgrowth. Taken together, these results indicate that TIS13 inhibits strigolactone biosynthesis in rice seedlings. We propose that TIS13 is a new lead compound for the development of specific strigolactone biosynthesis inhibitors.
Nine-cis-epoxycarotenoid dioxygenase (NCED), belonging to the family of carotenoid-cleaving dioxygenases (CCDs), is the ratelimiting step in the abscisic acid (ABA) biosynthetic pathway in plants. Abamine is the first reported abscisic acid biosynthesis inhibitor to target NCED. Its utility has also been considered in the inhibition of other enzymes. As CCDs other than NCED are also involved in the strigolactone biosynthetic pathway, abamine may affect strigolactone biosynthesis. In this study, we found that abamine decreases the level of strigolactones in several plant species and reduces the germination rate of Orobanche minor seeds co-grown with tobacco. Taken together, these data suggest that abamine may be used as a scaffold for the development of specific regulators of strigolactone production.
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