Abstract
Monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) are the two predominant galactolipids present in the photosynthetic membrane in many photosynthetic organisms, including algae and higher plants. These galactolipids are the main constituents of thylakoid membrane and are essential for chloroplast biogenesis and photoautotrophic growth. In silico analysis revealed that rice (Oryza sativa L.) genome has three genes encoding MGDG synthase (OsMGD1, 2, and 3). Although subcellular localization analysis demonstrated that OsMGD2 is localized to chloroplast, its expression was observed mainly in anther and endosperm, suggesting that MGDG might have an important role in the development of flower and grain in rice. Knock-out mutants of OsMGD2 were generated employing the CRISPR/Cas9 system and their morphology, yield and grain quality related traits were studied. The leaf of osmgd2 mutants showed reduced MGDG (∼11.6%) and DGDG (∼9.5%) content with chlorophyll a content decreased by ∼23%, consequently affecting the photosynthesis. The mutants also exhibited poor agronomic performance with plant height and panicle length decreased by ∼12.2 and ∼7.3%, respectively. Similarly, the number of filled grains per panicle was reduced by 43.8%, while the 1000 grain weight was increased by ∼6.3% in the mutants. The milled rice of mutants also had altered pasting properties and decreased linoleic acid content (∼26.6%). Put together, the present study demonstrated that OsMGD2 is the predominantly expressed gene encoding MGDG synthase in anther and grain and plays important roles in plant growth and development, as well as in grain quality.
Highlights
Galactolipids are a major class of higher plant glycerolipids, in which galactose is bound at the glycerol sn-3 position in O-glycosidic linkage to diacylglycerol
Phylogenetic analysis indicates that AtMGD1, OsMGD1, and ZmMGD1 belong to the type-A group, while AtMGD2 AtMGD3, OsMGD2, OsMGD3, ZmMGD2, and ZmMGD3 belonging to the type-B group form a separate clade (Supplementary Figure S1B)
AtMGD2 and AtMGD3 have only a limited role in thylakoid membrane biogenesis but under phosphate (Pi)-deficient conditions, type-B MGDG synthase supply MGDG required for DGDG synthesis, which is involved in maintaining cellular homeostasis by substituting for phosphoglycerolipids (Kobayashi et al, 2009)
Summary
Galactolipids are a major class of higher plant glycerolipids, in which galactose is bound at the glycerol sn-3 position in O-glycosidic linkage to diacylglycerol. OsMGD2 Contributes Grain Development and 20% of the chloroplast lipid, respectively (Dörmann and Benning, 2002; Kalisch et al, 2016). These galactolipids form the indispensable matrix in the thylakoid membrane of chloroplast, where photochemical and electron transport reactions of oxygenic photosynthesis occur (Mizusawa and Wada, 2012; Dörmann, 2013; Kobayashi et al, 2016). MGDG synthase is the principal enzyme for the synthesis of both MGDG and DGDG and has been found crucial for plant growth and development (Dörmann and Benning, 2002; Kalisch et al, 2016)
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