Objective MAX2 plays an important role in inhibiting plant branching and regulating strigolactone signaling pathway. MAX2 is also involved in multi-phytohormone interactions and in plant response to biotic and abiotic stresses. It has been shown that overexpression of Populus euphratica PeMAX2 can improve ionic homeostasis and the salt tolerance in transgenic plants of Arabidopsis thaliana. However, little is known about the function of PeMAX2 in drought tolerance. The objective of this study is to explore the mechanism of PeMAX2 in regulating drought tolerance of Arabidopsis thaliana.

Method P. euphratica PeMAX2 was overexpressed in A. thaliana, and the physiological and molecular mechanism underlying the osmotic and drought tolerance of transgenic plants was investigated in this study.

Result (1) The expression of PeMAX2 gene was up-regulated in P. euphratica leaves under long-term of drought stress. (2) After mannitol treatment, the seed germination rate and root length of A. thaliana overexpressing PeMAX2 were significantly higher than those of wild type and max2 mutant. The cell membrane was less damaged in PeMAX2-transgenic plants under osmotic stress compared with WT and max2. The increase of superoxide dismutase, peroxidase and catalase activities and the transcription levels of their encoding genes were higher in transgenic lines than in WT and max2 mutant under osmotic stress. As a result, the ability to regulate H₂O₂ was increased in root cells of transgenic lines. (3) A 10-d of soil drought decreased the chlorophyll content in all tested lines, and a more pronounced reduction was observed in WT and max2 mutant. Under drought stress, the maximum photochemical efficiency of PSⅡ, relative electron transport rate and actual quantum yield of photosynthesis were less inhibited in PeMAX2-overexpressed plants than in WT and max2. Meanwhile, transgenic plants had higher net photosynthetic rate and stomatal conductance under drought treatment, as compared with WT and mutant plants. This indicated that overexpression of PeMAX2 improved the photosynthetic capacity of transgenic plants under drought conditions. The recovery of chlorophyll content, fluorescence and photosynthesis of WT and mutant were significantly lower than that of transgenic lines after soil rehydration.

Conclusion Overexpression of P. euphratica PeMAX2 improves the drought tolerance of A. thaliana. This is mainly due to the increased ability to scavenge reactive oxygen species in transgenic plants. Consequently, the oxidative damage to cell membrane and the drought inhibition of photosynthesis are alleviated in PeMAX2-transgenic plants under water stress.