Signaling in the Arbuscular Mycorrhizal Symbiosis

Abstract

Many microorganisms form symbioses with plants that range, on a continuous scale, from parasitic to mutualistic. Among these, the most widespread mutualistic symbiosis is the arbuscular mycorrhiza, formed between arbuscular mycorrhizal (AM) fungi and vascular flowering plants. These associations occur in terrestrial ecosystems throughout the world and have a global impact on plant phosphorus nutrition. The arbuscular mycorrhiza is an endosymbiosis in which the fungus inhabits the root cortical cells and obtains carbon provided by the plant while it transfers mineral nutrients from the soil to the cortical cells. Development of the symbiosis involves the differentiation of both symbionts to create novel symbiotic interfaces within the root cells. The aim of this review is to explore the current understanding of the signals and signaling pathways used by the symbionts for the development of the AM symbiosis. Although the signal molecules used for initial communication are not yet known, recent studies point to their existence. Within the plant, there is evidence of arbuscular mycorrhiza-specific signals and of systemic signaling that influences phosphate-starvation responses and root development. The landmark cloning of three plant signaling proteins required for the development of the symbiosis has provided the first insights into a signaling pathway that is used by AM fungi and by rhizobia for their symbiotic associations with legumes.

Mycorrhizal responses to biochar in soil – concepts and mechanisms

“…The rhizosphere is a zone of intense signaling between microbes, including mycorrhizal fungi, and plant roots (Bais et al 2004;Harrison 2005;Bais et al 2006;Paszkowski 2006). For example, experiments conducted using both field soils and in vitro cultures show that compounds (e.g.…”

Indole-3-acetic acid: A widespread physiological code in interactions of fungi with other organisms

“…AM obtain carbon provided by the host plant while it transfers mineral nutrients from the soil to the cortical cells. 63 Symbiosis development involves the differentiation of both symbionts to create novel symbiotic interfaces within the root cells. Phytohormone-mediated signaling through hormones, such as auxin, gibberellin, and abscisic acid, is potentially involved in the establishment of AM symbiosis.…”

Cloning and characterisation of a maize carotenoid cleavage dioxygenase (ZmCCD1) and its involvement in the biosynthesis of apocarotenoids with various roles in mutualistic and parasitic interactions

“…For example, there are a number of reports showing that plants colonised by AM fungi are protected against subsequent infection with nematodes and plant pathogenic fungi (Borowicz 2001;Johansson et al 2004). This protection has been suggested to be due to improved nutritional status of the host but there is ample evidence that this cannot be the (only) explanation (Johansson et al 2004;Harrison 2005). Several studies have shown that during mycorrhizal symbiosis defence-related genes are induced (Pozo et al 2002;Kuster et al 2004).…”