Mechanisms of phytohormones in regulating arbuscular mycorrhiza development

Abstract:

Arbuscular mycorrhiza (AM) is a symbiont formed by the interaction and mutual recognition of soil-born AM fungi and the roots of most vascular plants in the long-term evolution. The development and function of AM, limited by environmental conditions, especially the soil nutrient level, drought, and salinity, depend on the precise "molecular dialogue" between AM fungi and host plants. Phytohormones are low-molecular-weight organics with low concentration and act as crucial signaling molecules in the regulation of AM symbiosis. There are mainly nine phytohormones participating in regulating AM development with different effects. Strigolactones (SLs) act at the first symbiotic recognition between AM fungi and host plants. At the early stage, abscisic acid (ABA) and brassinosteroid (BR) promote the fungal invasion, whereas salicylic acid (SA) and ethylene (ET) inhibit the fungal invasion. Auxin (Aux), ABA, and BR promote the subsequent arbuscule formation, whereas ET and gibberellin (GA) suppress the arbuscule formation. Jasmonic acid (JA) may have both positive and negative regulating effects on fungal invasion and arbuscule formation. However, the role of cytokinin (CTK) remains unclear in AM development. In addition, the signaling crosstalk among phytohormones normally determines AM development. This review summarized the characteristics of different phytohormones and their associated signaling crosstalk (synergistic or antagonistic) in regulating AM development, and the possible regulation mechanisms of different phytohormone signals involved in AM development under stress conditions. The profound research and systematical illustration of the physiological/molecular mechanisms of phytohormones in regulating the symbiotic relationships between AM fungi and host plants, will help the study on symbiology and the application of mycorrhizal technology.