Structure and function of natural and synthetic signalling molecules in parasitic weed germination

Abstract

The structures of naturally occurring germination stimulants for seeds of the parasitic weeds Striga spp. and Orobanche spp. are described. The bioactiphore in this strigolactone family of stimulants is deduced from a structure-activity relationship and shown to reside in the CD part of the stimulant molecule. A molecular mechanism for the initial stages of seed germination is proposed. The influence of stereochemistry on the stimulant activity is significant. Combining this molecular information leads to a model for the design of synthetic strigolactones. Nijmegen-1 is a typical example of a highly active, newly designed synthetic stimulant. The occurrence of natural stimulants not belonging to the strigolactone family, such as cotylenin and parthenolide, is briefly described. The biosynthesis of natural strigolactones from beta-carotene is analysed in terms of isolated and predicted stimulants. This scheme will be helpful in the search for new strigolactones from root exudates. Protein fishing experiments to isolate and characterise the receptor protein using biotin-labelled GR 24 are described. A receptor protein of 60 kD was identified by this method. Nijmegen-1 has been tested as a suicidal germination agent in field trials on tobacco infested by Orobanche ramosa L. The preliminary results are highly rewarding. Finally, some future challenges in synthesis are described. These include synthesising new natural and synthetic stimulants and establishing the molecular connection between strigolactones as germination stimulants, as the branching factor for arbuscular mycorrhizal fungi and as an inhibitor of shoot branching.

The Role of Root-Produced Volatile Secondary Metabolites in Mediating Soil Interactions

“…or Orobanche spp. population (Zwanenburg et al 2009). Furthermore, root volatiles might also have positive effects on neighboring plants.…”

Tomato strigolactones

“…1A). It has been reported that this enol ether bridge is not only essential for parasitic seed germination, 12,13 but is also required for the induction of AM branching 14 and their hormonal activity in planta. 15 Although the main structure of strigolactones is rather similar, their A-and B-ring decoration and stereochemistry can vary substantially (Fig.…”

Strigolactone Involvement in Root Development, Response to Abiotic Stress, and Interactions with the Biotic Soil Environment

“…A number of publications have discussed their implementation as inducers of suicidal seed germination of parasitic plant (Zwanenburg et al, 2009(Zwanenburg et al, , 2013Vurro and Yoneyama, 2012). However, strigolactones may be used in additional approaches for the development of new agricultural methodologies and technologies compatible with emerging concepts of sustainable agriculture.…”

“…Strigolactone inhibitors may be used to enhance rooting of plant cuttings (Rasmussen et al, 2012), potentially promoting the propagation of woody plants for the industry and conservation of endangered species. Today's new strigolactone analogs and mimics, which are under development or being synthesized (Zwanenburg et al, 2009;Prandi et al, 2011), are likely to substantially promote the ability to use strigolactones to the benefit of agriculture. Received June 9, 2014;accepted July 14, 2014;published July 18, 2014. LITERATURE CITED…”