Overexpression OsMGD In Tobacco Enhances The Tolerance To Multiple Stresses

Monogalactosyldiacylglycerol （MGDG） is an important seed plants galactolipid,which with digalactosyldiacylglycerol （DGDG） mainly exists in the photosyntheticmembrane and account for photosynthetic membrane galactolipid more than80%.MGDG and DGDG were not only involved in the constrction of a plant plastidmembranes and membrane formation of photosynthetic complexes, under thecondition of phosphorus deficiency can also replace missing phospholipids in plant.Monogalactosyldiacylglycerol synthetase （MGD） is a key enzyme for the synthesisof MGDG, so it is also considered as the key enzyme of photosynthetic membraneformation. Under the condition of phosphorus deficiency MGD activity is activated,the expression of MGD is increased under the drought and salt stress conditions.These show that MGD can improve the tolerance abilities of plants under multiplestresses. In this study, transgenic tobacco that overexpressing OsMGD and itsnon-transgenic control plant were used as materials and the hydroponics and the potculture were combined to study on whether overexpression of OsMGD in tobaccocan improve its tolerance in phosphorus deficiency, high salt and aluminum poisonconditions. In further, the function of OsMGD was initially explored. And then wegot these results as following:We cloned gene MGD from rice FR13A named OsMGD, and obtained thetransgenic tobacco plants by overexpression vector construction and Agrobacterium-mediated transformation and then measured its physiological indicators.Western blot analysis showed that MGD was expressed in tobacco, the MGDactivity in transgenic tobacco was significantly increased; Observation of the structure of chloroplast, transferred OsMGD makes the number of grana thylakoids significant increase in transgenic tobacco chloroplasts. Phospholipids （PC,PE and PG）, galactolipids （MGDG and DGDG） and fatty acid content in theoverexpression OsMGD tobacco leaves was significantly higher than that in the wild-type tobacco plants.Using overexpression OsMGD tobacco plants and the wild-type strain as experimental material, the plants were cultured for7days in nutrient solutionof low-phosphorus containing5μM NH₄H₂PO₄. We found that chlorophyll content in transgenic tobacco leaves was significantly higher than in wild-type plants under P deficiency, old leaves of transgenic plants does not appear chlorosis phenomenon which had been in wild-type leaves. Transgenic tobacco rootfresh weight and root to shoot ratio were both significantly higher than thewild-type. The plants were treated with200mM NaCl for10days in pots, and we found that the overall growth situation of transgenic tobacco is significantly better than the wild-type. Meanwhile, the aboveground biomass, chlorophyll content and photosynthetic rate were all significantly higher than wild-typeplants. Thylakoid membranes of the wild-type plants were completely destroyed after salt treatment, but it was observed that there were complete grana thylakoids in the transgenic plants. After plants were treated with500μM AlCl3in culture nutrition for24hours, we found that transgenic tobacco apical cell membrane integrity was significantly better than the wild-type tobacco through Evans blue staining; and the transgenic tobacco conductivity value was significantly lower than the wild-type tobacco. After recovery in the normal nutrient solution for3days, the recovery degree of the transgenic tobacco roots issignificantly better than the wild-type, and the root biomass was significantlyhigher than that of wild-type tobacco.From the above results, we can obtain: MGD was cloned from rice andsuccessfully transferred into the tobacco, with increased synthesis of transgenictobacco MGD, grana thylakoids number of leaves, and the contents of phospholipids,MGDG, DGDG and fatty acids are significantly increased. The increase ofphospholipids content in transgenic plants, which can still maintain the cellmembrane phospholipids on the level after the plant treated with phosphorusdeficiency, MGDG and DGDG substitute for lack of phospholipids increased thestability of cell membrane, improve the plant tolerance to low phosphorus. Becausegrana thylakoid number increased in transgenic plants, it can still maintain highphotosynthetic rate under the salt stress and then the tolerance of plants to salt stresswas improved. The increase of cell membrane stability in transgenic tobacco alsoimproved the tolerance of plants to aluminum toxicity. In conclusion, overexpressionOsMGD tobacco plant enhances its tolerance in the environment of phosphorus, saltstress and aluminum toxicity through changes in the molecular levels.