Overexpression of Rice Monogalactosyldiacylglycerol Synthase OsMGD Leads to Enhanced Salt Tolerance in Rice

Monogalactosyldiacylglycerol (MGDG) is the most abundant lipid on earth and constitutes about 50% of the polar lipids in the thylakoid membrane of higher plants. MGDG synthase (MGD) is the key enzyme responsible for MGDG synthesis in plants. However, so far, the function of the MGD gene in plant stress responses is still unknown, especially in crop plants. In this study, the performances of wild-type rice (Oryza sativa L. Nipponbare), OsMGD overexpression, and RNA interference lines were analyzed under salt stress to clarify the role of OsMGD in rice under salt stress. The results showed that, after 6 days of NaCl treatment, OsMGD-overexpressing rice seedlings had higher biomass than the wild-type rice, with significantly lower Na+ content and Na+ to K+ ratio in the shoots. Meanwhile, overexpression lines showed a significant increase in the contents of chlorophyll a and carotenoid and photosynthetic capabilities, including the net photosynthetic rate, maximal quantum yield (Fv/Fm), effective PSII quantum yield (Phi(PSII)), electron transport rate (ETR), and coefficient of photochemical quenching (qP), compared with the wild-type line. Also, OsMGD overexpression lines contained higher MGDG and 18:3 unsaturated fatty acid levels under salt stress. These results indicate that OsMGD participates in the regulation of improving salt tolerance through protecting photosynthetic capabilities and ion balance in rice.