Regioselective and stereospecific hydroxylation of GR24 by Sorghum bicolor and evaluation of germination inducing activities of hydroxylated GR24 stereoisomers toward seeds of Striga species

Abstract

Bioconversion of GR24, the most widely used synthetic strigolactone (SL), by hydroponically grown sorghum (Sorghum bicolor) and biological activities of hydroxylated GR24 stereoisomers were studied. Analysis of extracts and exudates of sorghum roots previously fed with a racemic and diastereomeric mixture of GR24, using liquid chromatography-tandem mass spectrometry with multiple reaction monitoring (MRM), confirmed uptake of GR24 and suggested its conversion to mono-hydroxylated products. Two major GR24 metabolites, 7-hydroxy-GR24 and 8-hydroxy-GR24, were identified in the root extracts and exudates by direct comparison of chromatographic behavior with a series of synthetic mono-hydroxylated GR24 analogues. Separate feeding experiments with each of the GR24 stereoisomers revealed that the hydroxylated products were derived from 2'-epi-GR24, an evidence of sterical recognition of the GR24 molecule by sorghum. Trans-4-hydroxy-GR24 isomers derived from all GR24 stereoisomers were detected in the exudates as minor metabolites. The synthetic hydroxy-GR24 isomers induced germination of Striga hermonthica in decreasing order of C-8>C-7>C-6>C-5>C-4. In contrast the stereoisomers having the same configuration of orobanchol, irrespective of position of hydroxylation, induced germination of Striga gesnerioides. The results confirm previous reports on structural requirements of SLs and ascribe a critical role to hydroxylation, but not to the position of the hydroxyl group in the AB part of the molecule, in induction of S. gesnerioides seed germination.

Bioconversion of 5-deoxystrigol stereoisomers to monohydroxylated strigolactones by plants

“…3) will decrease the activities of exogenous SLs, since the activities of HO-SLs were lower than those of deoxy-SLs on the inhibition of shoot branching in rice 35) and the induction of seed germination against Striga hermonthica. 36) The production of endogenous SL was little inhibited by the administration of deoxy-SLs in both the red bell pepper and the sunflower. This result implies the possibility that hydroxylation of exogenous deoxy-SLs is a metabolic reaction distinct from endogenous SL biosynthesis.…”

Hybrid‐type strigolactone analogues derived from auxins

“…published 3′‐methyl‐GR24 having an EC 50 value one order of magnitude higher than that of GR24 on P. ramosa and comparable with GR24 for O. minor . Several hydroxylated analogues of GR24 showed germination‐stimulating activity at 0.1 μ m , but results at lower concentrations were not tested …”

“…51 Several hydroxylated analogues of GR24 showed germination-stimulating activity at 0.1 μM, but results at lower concentrations were not tested. 52 Pest Manag Sci 2019; 75: 3113-3121 © 2019 The Authors.…”

Strategies for the synthesis of canonical, non-canonical and analogues of strigolactones, and evaluation of their parasitic weed germination activity

“…Given that this tricyclic intermediate can be synthesized in 55% yield following route A in Scheme 10, the global yield for synthesis of 28 is 4.4% (1.8% in the case of 29). In a subsequent study, 28 showed activity in the germination of S. hermonthica (but only limited activity for Striga gesnerioides), and was found to be more active than the GR24 analogue epimer at C-4 (Ueno et al 2015). Similarly, the study by Malik et al (2011) presents the synthesis of similar analogues hydroxylated or acetylated at C-4, as well as others containing a ketone group.…”

“…After butenolide ring addition, the two analogues PLN655 and PLN655a were obtained in 43% and 48% overall yield respectively. The former, together with its nonnitrogen-containing derivative PLC655, which was also synthesized, were tested on O. aegyptiaca as racemates and their activity levels found to be higher than those for GR24: both were highly active at 10 -4 and 10 -6 M, with percentages of around 80-90%, and PLN655 retained this level down to 10 -8 M. Ueno et al (2015) synthesized the GR24 analogues monohydroxylated at each aromatic position of the A-ring (C-5, C-6, C-7 or C-8; Scheme 19). The starting materials in this case were four hydroxylated indan-1one derivatives isolated from root exudates of hydroponically grown Sorghum bicolor.…”