On improving strigolactone mimics for induction of suicidal germination of the root parasitic plant Striga hermonthica
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aBIOTECH
R E S E A RC H A RT I C L E
On improving strigolactone mimics for induction of suicidal germination of the root parasitic plant Striga hermonthica Ikuo Takahashi1 , Kosuke Fukui1 , Tadao Asami1& 1
Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
Received: 2 July 2020 / Accepted: 10 October 2020
Abstract
Strigolactones (SLs) are plant hormones that regulate the branching of plants and seed germination stimulants of root parasitic plants. As root parasites are a great threat to agricultural production, the use of SL agonists could be anticipated to provide an efficient method for regulating root parasites as suicidal germination inducers. A series of phenoxyfuranone-type SL mimics, termed debranones, has been reported to show potent bioactivities, including reduction of the tiller number on rice, and stimulation of seed germination in the root parasite Striga hermonthica. To exert both activities, two substituents on the phenyl ring of the molecules were important but at least a substituent at the 2-position must be an electron-withdrawing group. However, little is known about the effect of the properties of the substituents at the 2-position on bioactivities. Here, we found that different substituents at the 2-position give different preferences for bioactivities. Halogenated debranones were more effective than the others and SL agonist GR24 for inhibiting rice tiller but far less effective in the induction of S. hermonthica germination. Meanwhile, nitrile and methyl derivatives clearly stimulated the germination of S. hermonthica seeds. Although their IC50 values were 100 times higher than that of GR24 in the receptor competitive binding assay, their physiological activities were approximately 1/10 of GR24. These differences could be due to their uptake in plants and/or their physicochemical stability under our experimental conditions. These findings could support the design of more potent and selective SL agonists that could contribute to solving big agricultural issues.
Keywords Agonist, Rice, Root parasitic weed, Seed germination, Strigolactone, Tillering
INTRODUCTION The root parasitic Orobanchaceae plants Striga, Orobanche, and Phelipanche spp. infect economically important crops and inflict severe damage to agricultural production around the world. The economic loss caused by Striga amounts to approximately 200 million US dollars per year and increases by 30 million US dollars annually (Rodenburg et al. 2016). The infestation of root parasitic plants is a widespread concern in sub-Saharan Africa, where a 40–100% yield reduction has been reported in fields infested with root parasites, & Correspondence: [email protected] (T. Asami)
with an annual loss from rice cultivation estimated at 60–700 million US dollars (Rodenburg et al. 2011; Schut et al. 2015). Striga infests more than 40% of sub-Saharan Africa’s crop-producing areas, affecting the lives of 100 million people (Scholes and Press 2008). Almost all of the root parasitic Orobanchaceae
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