Selective Mimics of Strigolactone Actions and Their Potential Use for Controlling Damage Caused by Root Parasitic Weeds

Strigolactones (SLs) are a novel class of plant hormones and rhizosphere communication signals, although the molecular mechanisms underlying their activities have not yet been fully determined. Nor is their application in agriculture well developed. The importance of plant hormone agonists has been demonstrated in both basic and applied research, and chemicals that mimic strigolactone functions should greatly facilitate strigolactone research. Here, we report our discovery of a new phenoxyfuranone compound, 4-Br debranone (4BD), that shows similar activity to that of the major strigolactone (SL) analog GR24 in many aspects of a biological assay on plants. 4BD strongly inhibited tiller bud outgrowth in the SL-deficient rice mutant d10 at the same concentration as GR24, with no adverse effects, even during prolonged cultivation. This result was also observed in the Arabidopsis thaliana SL-deficient mutants max1, max3, and max4. However, the application of 4BD to the Arabidopsis SL-insensitive mutant max2 induced no morphological changes in it. The expression of SL biosynthetic genes was also reduced by 4BD treatment, probably via negative feedback regulation. However, in a seed germination assay on Striga hermonthica, a root parasitic plant, 4BD showed far less activity than GR24. These results suggest that 4BD is the first plant-specific strigolactone mimic.