Effects of Monogalactoglycerolipid Deficiency and Diacylglycerol Acyltransferase Overexpression on Oil Accumulation in Transgenic Tobacco

Engineering accumulation of triacylglycerol (TAG) in vegetative tissues has been recently proposed as a promising strategy for increasing plant oil production. However, little is known about regulatory mechanisms involved in increasing oil production in plant vegetative tissues. In this study, expression of NtMGD1 encoding a major biosynthetic enzyme for the chloroplast membrane lipid was inhibited by RNAi interference in tobacco. Furthermore, AtDGAT1 , a rate-regulating gene involved in TAG biosynthesis, was ectopically overexpressed. Results showed that leaf TAG accumulations were significantly increased both by NtMGD1 RNAi and AtDGAT1 overexpression. However, combination of AtDGAT1 overexpression with NtMGD1 RNAi did not result in additive increase in TAG accumulation in leaves than AtDGAT1 overexpression or NtMGD1 RNAi alone. In addition, reduction of monogalactosyldiacylglycerol (MGDG) biosynthesis by NtMGD1 RNAi was relieved by AtDGAT1 overexpression. Expression of lipid transfer protein (LTP) was upregulated both by AtDGAT1 overexpression and NtMGD1 RNAi and correlated with increased oil accumulation in leaves. Our results indicated that fatty acids deesterified from chloroplast membrane galactolipids could be redirected into TAG. TAG is an energy-dense molecule that might act as a storage pool for carbohydrate. This membrane lipid remodeling may represent an adaptive response that enables plant cells to avoid toxic effects of free fatty acids.