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. 2021 Sep 17:12:725949.
doi: 10.3389/fpls.2021.725949. eCollection 2021.

Synthesis and Evaluation of New Halogenated GR24 Analogs as Germination Promotors for Orobanche cumana

Yuchao Chen  1   2   3 , Yi Kuang  4 , Liyang Shi  4 , Xing Wang  4 , Haoyu Fu  4 , Shengxiang Yang  4 , Diego A Sampietro  5 , Luqi Huang  1   2 , Yuan Yuan  2
Affiliations

Synthesis and Evaluation of New Halogenated GR24 Analogs as Germination Promotors for Orobanche cumana

Yuchao Chen et al. Front Plant Sci. .

Abstract

Orobanche and Striga are parasitic weeds extremely well adapted to the life cycle of their host plants. They cannot be eliminated by conventional weed control methods. Suicidal germination induced by strigolactones (SLs) analogs is an option to control these weeds. Here, we reported two new halogenated (+)-GR24 analogs, named 7-bromo-GR24 (7BrGR24) and 7-fluoro-GR24 (7FGR24), which were synthesized using commercially available materials following simple steps. Both compounds strongly promoted seed germination of Orobanche cumana. Their EC50 values of 2.3±0.28×10-8M (7BrGR24) and 0.97±0.29×10-8M (7FGR24) were 3- and 5-fold lower, respectively, than those of (+)-GR24 and rac-GR24 (EC50=5.1±1.32-5.3±1.44×10-8; p<0.05). The 7FGR24 was the strongest seed germination promoter tested, with a stimulation percentage of 62.0±9.1% at 1.0×10-8M and 90.9±3.8% at 1.0×10-6M. It showed higher binding affinity (IC50=0.189±0.012μM) for the SL receptor ShHTL7 than (+)-GR24 (IC50=0.248±0.032μM), rac-GR24 (IC50=0.319±0.032μM), and 7BrGR24 (IC50=0.521±0.087μM). Molecular docking experiments indicated that the binding affinity of both halogenated analogs to the strigolactone receptor OsD14 was similar to that of (+)-GR24. Our results indicate that 7FGR24 is a promising agent for the control of parasitic weeds.

Keywords: GR24 analogs; Orobanche cumana; parasitic weeds; strigolactones; suicidal germination.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Synthesis of (+)-GR24.
Figure 2
Figure 2
Synthesis of (−)-epi-GR24.
Figure 3
Figure 3
Synthesis of 7-bromo-GR24 (7BrGR24) and 7-fluoro-GR24 (7FGR24), respectively.
Figure 4
Figure 4
Relative fluorescence unit (FU) values were recorded for rac-GR24, (+)-GR24, and the halogenated (+)-GR24 analogs when tested at several concentrations in the yoshimulactone green (YLG) assay. IC50 values for these strigolactone (SL) analogs were calculated. Values represent means±SD (n=4).
Figure 5
Figure 5
Docking modes of (−)-epi-GR24 and the halogenated (+)-GR24 analogs with OsD14. (A) Pocket location of OsD14 when 7FGR24 combined on it. (B) Spatial position and interaction force between 7FGR24 and important amino acid residues in the active pocket. (C) The distance of the polar connection between the 7FGR24/(+)-GR24 and Ser 97 and His 247. (D) The halogenated (+)-GR24 analogs in the active pocket (the yellow sticks in the pocket are SER97). (E) 2D view of 7FGR24 in the catalytic site of OsD14. (F) Comparison of binding postures of 7FGR24, 7BrGR24, and (+)-GR24. (G) Two ways of connecting (−)-epi-GR24 to active pocket. The (−)-epi-GR24 is shown as yellow and purple sticks, 7BrGR24 as orange sticks, 7FGR24 as blue sticks, and the original ligand of OsD14 – (+)-GR24 as green sticks.
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