Mobilization of storage lipid reserve and expression analysis of lipase and lipoxygenase genes in rice (Oryza sativa var. Pusa Basmati 1) bran during germination

Storage lipid mobilization by lipases and lipoxygenases (LOXs) in response to developmental cues take place during seed germination. After rice grain milling, the endogenous lipases and LOXs present in the bran fraction come in contact with the storage lipid reserve or triacylglycerol (TAG). Lipases catalyze the hydrolysis of TAGs to non-esterified fatty acids (NEFAs) and glycerol. The NEFAs, especially linoleic acid (18:2) produced, are further subjected to oxidative rancidity via peroxidation reaction catalyzed by LOXs. This results in the production of conjugated hydroperoxides of 18:2 that influence the off-flavors in rice bran lipids. The aim of this study is to understand how lipid mobilization and expression of lipase and LOX genes occur in the bran of germinating rice grains ( Oryza sativa var. Pusa Basmati 1 ). Our results show that the primary source of storage lipids in bran is TAG, and its mobilization starts at 4 days after imbibition (4 DAI). Using publically available RNA-seq data and phylogeny analyses, we selected a total of 18 lipase and 16 LOX genes in rice for their expression profiles during onset of lipid mobilization. Gene expression analyses revealed OsLip1 , OsLip9 , and OsLip13 ; and OsLOX3 and OsLOX14 as the predominantly expressed genes in bran of germinating rice grains. This study explores two important events in the germinating rice grains, namely, mobilization of storage lipids and expression pattern of lipase and LOX genes. The information generated in this study can be used to efficiently manipulate the genes to enhance the shelf-stability of bran lipid reserve. Lipases and lipoxygenases (LOX) decompose the storage lipid reserve in rice bran. Lipid mobilization and expression pattern of lipase and LOX genes were studied in bran fraction of germinating rice grains. • During rice grain germination, mobilization of stored lipid reserves in bran started after 4 DAI. • Lipases and LOXs were highly expressed in bran and coincided with lipid mobilization. • OsLip1 , OsLip9 , and OsLip13 ; and OsLOX3 and OsLOX14 showed elevated transcript expression pattern in rice bran.