Phytohormone Mimics for the Study of Striga

　Striga is a parasitic plant called “witchweed” that has been significantly reducing the amount of grains yield especially in Africa.¹⁾ Striga germinates by detecting strigolactone, a plant hormone produced from a host plant but the strigolactone receptor had not been identified and the detailed mechanism had not been revealed. Then Hagiwara et al. developed Yoshimulactone Green (YLG, 1),²⁾ a fluorescent agonist which act on strigolactone receptor. 1 binds to a protein ShHTL which is a strigolactone receptor, and strong green fluorescent products are generated after being hydrolyzed by ShHTL.

　Tsuchiya et al. established an assay to measure IC₅₀ of YLG against ShHTL, and they explored and screened compounds which strongly binds to ShHTL. Finally they discovered Sphynolactone-7 (SPL7, 2), a strigolactone mimic which binds very strongly to ShHTL7, and they found that it can force Striga to germinate and wither in soil without the host plant as a nutrient source.³⁾ The activity of SPL7 against Striga germination is extremely high compared with other existing strigolactone analogs like GR24,⁴⁾ but SPL7 binds specifically to the strigolactone receptor of Striga. Furthermore, SPL7’s bioactivity as other plants’ hormone is very weak. So it is expected to be used as a revolutionary control method against Striga.