Structural requirements of strigolactones for germination induction and inhibition of Striga gesnerioides seeds

Abstract

Structure-activity relationship studies of strigolactones and Striga gesnerioides seed germination revealed strict structural requirements for germination induction and a new function of the plant hormones as germination inhibitors. Stereoisomers of the naturally occurring strigolactones, strigol, sorgolactone, orobanchol, sorgomol and 5-deoxystrigol, 36 in total, were prepared and screened for the ability to induce and/or inhibit the germination of Striga hermonthica and Striga gesnerioides seeds collected from mature plants that parasitized on sorghum and cowpea, respectively. All of the compounds induced S. hermonthica seed germination, albeit displayed differential activities. On the other hand, only a limited number of the compounds induced significant germination in S. gesnerioides, thus indicating strict structural requirements. Strigolactones inducing high germination in S. gesnerioides induced low germination in S. hermonthica. Strigolactones with the same configuration at C3a, C8b and C2' as that in 5-deoxystrigol (9a) induced high germination of S. hermonthica seeds, but most of them inhibited the germination of S. gesnerioides. The differential response of S. gesnerioides to strigolactones may play an important role in the survival of the species. However, the compounds could be used as means of control if mixed cropping of cowpea and sorghum is adopted.

Securing Important Strigolactone Key Structures: Orobanchol and 5‐Deoxystrigol

“…One of these stereoisomers was subjected to X-ray diffraction analysis, which identified the structure of this compound as isomer 12b. Gratifyingly, the X-ray structure (Figure 4) was in full agreement with the structure assigned by CD spectra applying Welzel's rule, [23,26,28] i.e., the (3aS,8bR,2′R) configuration, with a negative Cotton effect in the 270 nm region of the CD spectrum, thus corresponding to (-)-ent-2′-epi-5-deoxystrigol. Having determined the absolute configuration of stereoisomer 12b, the remaining peaks in the chiral HPLC chromatograms could be attributed to the enantiopure 5-deoxystrigol stereoisomers 1b, 11b, and 12a, respectively, using the CD correlation diagrams (Figure 3).…”

“…[1,6] ). [14,22,23,28] Biosynthetically, (+)-5-deoxystrigol originates from carlactone, [24,25] and it plays a key role in SL research. Note that carlactone is not an SL, but is accepted as a precursor of SLs.…”

Mutation in sorghum LOW GERMINATION STIMULANT 1 alters strigolactones and causes Striga resistance

“…In a comparison of all possible stereoisomers of the SLs previously reported in sorghum root exudates, strigol, sorgolactone, sorgomol, and 5-deoxystrigol, it was shown that S. hermonthica germination was much higher when exposed to these SLs in their natural (β-oriented C-ring) form than when treated with their α-oriented enantiomers (16). Furthermore, Yoneyama et al (28) predicted that SLs containing a hydroxyl group directly on the A-(e.g., strigol) or B-ring (e.g., orobanchol) would be prone to ring-destroying nucleophilic attack and therefore be less persistent in the soil.…”

Strigolactone Hormones and Their Stereoisomers Signal through Two Related Receptor Proteins to Induce Different Physiological Responses in Arabidopsis

“…, show the greatest activity toward stimulating germination of Striga hermonthica seed, with their enantiomers inducing a lower response (Thuring et al, 1997;Sugimoto et al, 1998;Nomura et al, 2013;Zwanenburg and Pospísil, 2013). However, germination in Striga gesnerioides is inhibited by isomers that promote germination in S. hermonthica and stimulated by orobanchol-type analogs .…”

“…However, such studies have not been reported for O. minor. To allow direct comparison with the work by Nomura et al (2013), we tested deoxySL stereoisomers at 10 nM and 1 mM on O. minor seed germination. As previously reported (Nelson et al, 2009), rac-GR24 stimulated O. minor seed germination, whereas KAR 1 did not (Fig.…”