Arbuscular Mycorrhizal Fungi Regulate MAPK Pathway Genes Expression and Enhance Drought Tolerance of Populus Simonii × P. Nigra Seedlings

Abstract

Background: Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with host plants, which can promote plants to absorb more water and nutrients, and thus improve the stress resistance of plants. Our study aimed to investigate the effects of Rhizophagus irregularis on Populus simonii × P. nigra seedlings under drought stress. Results: The experiment was a completely random design with two water conditions (well-watered or drought stress) and two AMF treatments (inoculated with or without R. irregularis). Our results showed that mycorrhizal seedlings performed less oxidative damage and stronger tolerance of drought, which recorded higher photosynthesis and less concentrations of Malondialdehyde (MDA), H2O2, and proline under drought stress versus non-mycorrhizal seedlings. Under drought stress, AMF inoculation reduced soluble sugar concentration in leaves but promoted its accumulation in roots. The superoxide dismutase (SOD) activity in leaves and roots, and catalase (CAT) activity in roots of mycorrhizal seedlings were lower than non-mycorrhizal seedlings, but CAT activity in leaves of mycorrhizal seedlings was higher than non-mycorrhizal seedlings under drought stress. Drought stress and AMF inoculation both induced the expressions of MAPKs of P. simonii × P. nigra, but the expression patterns of MAPKs under four treatments were obviously different.Conclusions: Overall, our results demonstrated that mycorrhizal seedlings had less oxidative damage and stronger tolerance to drought. MAPKs expressions of P. simonii×P. nigra (PsnMAPKs) were induced by drought stress and AMF inoculation, and the expression patterns of PsnMAPKs in response to drought stress were different between mycorrhizal and non-mycorrhizal seedlings. Non-mycorrhizal seedlings may be adapted to drought by up-regulating MAPKs expressions leading to stomatal closure. Drought stress decreased serval PsnMAPKs expressions induced by AMF inoculation, which may be associated with mycorrhizal colonization.