Molecular process of arbuscular mycorrhizal associations and the symbiotic stabilizing mechanisms

Abstract

AM fungi are coenocytic and heterokaryotic can recognize various plant hosts. During the development of arbuscular mycorrhizal (AM) symbiosis, AM fungus at first senses the signals exuded by host plants, and then secretes corresponding Myc factors to dialogize with the plants. The host plant discriminates the Myc factors by superficial receptors located on the epidermal cells, and then initiates the symbiotic cascade, triggering the release of calcium from nuclear membrane, which leads to the calcium oscillations in perinuclear region. After decodes calcium oscillations, a nuclear-localized calcium and calmodulin- dependent protein kinase (CCaMK) phosphorylates corresponding substrates and then activates transcription factors, inducing the expression of symbiosis-related genes. Different genes induced at different symbiotic stages work together to arrive at the final goal of forming AM. Such a symbiosis has evolved hundreds of millions of years, and has reached a high overall coordination. Cooperation between different species is intrinsically unstable. Rather, the mutualism is evolutionarily stable, because the partners cooperate to stabilize this joint through a fair resource partitioning mechanisms or beyond, which let AM coevolves from past to the future. Here, we give a comprehensive view about the molecular process of AM formation and the stabilizing mechanisms of this system. Key words: Arbuscular mycorrhizal fungi, symbionts, symbiosis stability, lipochitooligosaccharide, calcium oscillations.