镁营养调控光合碳运输和分配促进菌根共生的生理和分子机制

与菌根真菌共生提高了作物养分效率，但也增加了根系的碳库压力。镁参与植物光合碳同化和运输，那么，镁是否会通过调控光合碳运输和分配促进菌根共生鲜有报道。在前期研究中，我们鉴定到两个施镁条件下受菌根诱导增强表达的大豆GmSWEET7和GmSWEET14基因。本项目首先研究不同镁浓度对碳消耗强度不同的丛枝菌根真菌接种效果和植株碳分配的影响，明确GmSWEET7和GmSWEET14对镁及菌根接种的表达响应；接着，利用GmSWEET7和GmSWEET14过量和敲除转基因大豆，结合13C同位素标记，研究施镁对这两个基因参与菌根植物体内光合碳运输和分配的影响；并且，通过酵母功能互补结合转基因根系分泌物鉴定，确定GmSWEET7和GmSWEET14的糖转运特性；利用启动子融合GUS转基因大豆，确定其在菌根植物中的定位。最终阐明施镁通过GmSWEETs调控植物光合碳运输和分配，促进菌根共生的生理和分子机制。

Symbiosis with arbuscular mycorrhizal fungi (AMF) plays very important roles in improvement of nutrient efficiency, but it also increases the pressure of carbon sink to plant roots. Magnesium (Mg) involves in assimilation and transport of photosynthetic carbon in plants. However, whether Mg promotes mycorrhizal symbiosis by regulating carbon transport and allocation seldom has been reported. In the previous study, GmSWEET7 and GmSWEET14 induced by mycorrhizal inoculation were identified under Mg application conditions. In this project, firstly, the effects of different Mg concentrations on inoculation efficiency of AMF with different carbon cost intensity and carbon allocation will be assessed in plants, and the expression patterns of mycorrhiza-induced GmSWEET7 and GmSWEET14 will be investigated in responses to Mg application and AMF inoculation. Subsequently, over-expressing and knock-out transgenic soybean followed by 13C labeling technique will be employed to elucidate the effect of Mg application on these two genes involved in photosynthetic carbon transport and allocation in mycorrhizal plants. Furthermore, sugar transport characteristics of GmSWEET7 and GmSWEET14 will be determined by yeast functional complementary system combined with identification of transgenic root exudates. Promoter-GUS transgenic soybean plants will be employed to analyze the localization of GmSWEET7 or GmSWEET14 in the mycorrhizal plants. The results will elucidate the physiological and molecular mechanisms of Mg application regulating photosynthetic carbon transport and allocation through GmSWEETs, and thereby promoting mycorrhizal symbiosis in plants.