Optimization of the KK5 Scaffold and Biological Evaluation of KK5 Derivatives to Identify Potent Strigolactone Biosynthesis Inhibitors

Strigolactones (SLs) are germination stimulants for root-parasitic weeds, such as <i>Striga</i> spp., <i>Orobanche</i> spp., and <i>Phelipanche</i> spp., which cause significant damage to agricultural crops. Manipulation of SL biosynthesis using SL biosynthesis inhibitors can suppress the damage caused by these root-parasitic weeds. Therefore, in this study, we aimed to optimize the structure of the previously reported SL biosynthesis inhibitor KK5 and evaluate the effects of its derivatives on SL biosynthesis. A structure-activity relationship study revealed that 4-(2-phenoxyethoxy)-1-phenyl-3-(1<i>H</i>-1,2,4-triazol-1-yl)butanone (KeIKK5) inhibited 4-deoxyorobanchol biosynthesis in rice more potently than KK5. Additionally, germination assays revealed that KeIKK5 treatment inhibited the germination of root-parasitic weeds. Overall, our data highlight KeIKK5 as a potent SL biosynthesis inhibitor that suppresses the damage caused by root-parasitic weeds.