Effect of the strigolactone analogs methyl phenlactonoates on spore germination and root colonization of arbuscular mycorrhizal fungi

Strigolactones (SLs), a novel class of plant hormones, are key regulator of plant architecture and mediator of biotic interactions in the rhizosphere. Root-released SLs initiate the establishment of arbuscular mycorrhizal (AM) symbiosis by inducing spore germination and hyphal branching in AM fungi (AMF). However, these compounds also trigger the germination of root parasitic weeds, paving the way for deleterious infestation. Availability of SLs is required for investigating of their functions and also for application in agriculture. However, natural SLs are difficult to synthesize due to their complex structure and cannot be isolated at large scale, as they are released at very low concentrations. Therefore, there is a need for synthetic SL analogs. Recently, we reported on the development of simple SL analogs, methyl phenlactonoates (MPs), which show high SL activity in plants. Here, we investigate the effect of MP1, MP3 and the widely used SL-analog GR24 on AMF spore germination and host root colonization. Our results show that MP1 and MP3 inhibit AMF spore germination, but promote the intra-radical root colonization, both more efficiently than GR24. These results indicate that field application of MP1 and MP3 does not have negative impact on mycorrhizal fungi. In conclusion, our data together with the previously reported simple synthesis, high activity in regulating plant architecture and inducing Striga seed germination, demonstrate the utility of MP1 and MP3 as for field application in combating root parasitic weeds by inducing germination in host's absence

The apocarotenoid metabolite zaxinone regulates growth and strigolactone biosynthesis in rice

Strigolactone and abscisic acid are carotenoid-derived plant hormones. Here the authors describe the identification of zaxinone, a further apocarotenoid metabolite, which down-regulates strigolactone content and is required for normal growth and development in rice

Methylation at the C-3′ in D-Ring of Strigolactone Analogs Reduces Biological Activity in Root Parasitic Plants and Rice

Strigolactones (SLs) regulate plant development and induce seed germination in obligate root parasitic weeds, e.g. Striga spp. Because organic synthesis of natural SLs is laborious, there is a large need for easy-to-synthesize and efficient analogs. Here, we investigated the effect of a structural modification of the D-ring, a conserved structural element in SLs. We synthesized and investigated the activity of two analogs, MP13 and MP26, which differ from previously published AR8 and AR36 only in the absence of methylation at C-3′. The de-methylated MP13 and MP26 were much more efficient in regulating plant development and inducing Striga seed germination, compared with AR8. Hydrolysis assays performed with purified Striga SL receptor and docking of AR8 and MP13 to the corresponding active site confirmed and explained the higher activity. Field trials performed in a naturally Striga-infested African farmer’s field unraveled MP13 as a promising candidate for combating Striga by inducing germination in host’s absence. Our findings demonstrate that methylation of the C-3′ in D-ring in SL analogs has a negative impact on their activity and identify MP13 and, particularly, MP26 as potent SL analogs with simple structures, which can be employed to control Striga, a major threat to global food security

Nitro-Phenlactone, a Carlactone Analog with Pleiotropic Strigolactone Activities

International audienceStrigolactones (SLs) are novel phytohormones that shape plant architecture by inhibiting shoot branching and regulating root growth, besides their established functions in stimulating seed germination of root-parasitic weeds, such as Striga and Phelipanche species, and inducing hyphal branching in arbuscular mycorrhizal (AM) fungi (Al-Babili and Bouwmeester, 2015). Canonical SLs are divided into strigol- and orobanchol-like subfamilies with a typical structure consisting of a tricyclic (ABC-ring) and a monocyclic lactone (D-ring), which are connected by an enol ether bridge (Figure 1A and Supplemental Figure 1). SLs are synthesized from carotenoids via carlactone, which lacks the B/C-ring (Alder et al., 2012). In Arabidopsis, carlactone (Figure 1A) is converted by MAX1, a member of the CYP711 family, into carlactonoic acid, after methylation, which, can bind to SL receptor (Abe et al., 2014). In rice, a MAX1 homolog, the carlactone oxidase, introduces B/C-rings into carlactone, yielding 4-deoxyorobanchol (Supplemental Figure 1) (Zhang et al., 2014), the precursor of canonical orobanchol-like SLs. SL perception involves an α/β-fold hydrolase (D14 in rice) that acts as a receptor and the SCF-type ubiquitin ligase MAX2 (D3 in rice) that mediates degradation of target proteins, such as members of the SMAX1-LIKE (SMXL; D53 in rice) family of chaperonin-like proteins (Bennett and Leyser, 2014). By interacting with D14 homolog KAI2, MAX2 mediates also signal transduction of karrikins, smoke-derived compounds that act as growth regulators inhibiting hypocotyl growth and inducing seed germination in Arabidopsis but not in root-parasitic weeds (Smith and Li, 2014)