Deciphering molecular mechanisms regarding enhanced drought tolerance in plants by arbuscular mycorrhizal fungi

Soil drought, an important abiotic stress, seriously inhibits plant growth and physiological activities. However, arbuscular mycorrhizal (AM) fungi in soil can enhance plant adaptability and tolerance to drought stress after establishing mycorrhizal symbiosis with plant roots. Studies on AM fungi-enhanced host drought tolerance are involved in physiological, morphological and molecular levels, with a focus on physiological mechanisms. Study on the molecular mechanisms explaining how arbuscular mycorrhizae enhance plant drought tolerance has being lagging behind that on the physilogical mechanisms, however, increasingly accumulated experiments have focused on the molecular mechanisms during the past decade. This review addresses the question of which functional and regulatory genes in host plants are involved in AM fungi-modulated drought tolerance of host plants, and highlights how these genes play the role in physiological activities such as osmoregulation, water and nutrient transport, hormones, and signal transduction under mycorrhization. The review also outlines how mycorrhizal plants modulate plant drought tolerance through the regulation of transcription factors (GRAS, MYB and AP2/ERF), and prospects an outlook for future research in exploring the interaction of signal pathways in gene regulation of mycorrhizal plants.