Genetic and genomic approaches to address rapid rancidity of rice bran

Rice bran is an invaluable by-product of paddy processing industry. It is rich in minerals, protein, lipids, and crude fiber. In addition, it also possesses compounds with anti-oxidant, anti-allergic, anti-diabetic, and anti-cancer properties. It forms a basis for the extraction of rice bran oil and preparation of various functional foods with health benefits and potential to prevent chronic health issues. Nevertheless, the rapid deterioration of bran upon storage acts as a major limitation in exploiting the full potential of rice bran. In this review, we have discussed three strategies to address rapid rancidity of rice bran and enhance its shelf life and storability vis-a-vis emphasizing the importance of rice bran in terms of its nutritional composition. One strategy is through exploitation of the null mutations in the genes governing lipases and lipoxygenases leading to nonfunctional enzymes (enzyme deficient approach), another strategy is through reducing the PUFA content that is more prone to oxidation (substrate deficient approach) and a third strategy is through enhancing the antioxidant content that effectively terminate the lipid peroxidation by donating the hydrogen atom.

A Conserved Glycine Is Identified to be Essential for Desaturase Activity of IpFAD2s by Analyzing Natural Variants from Idesia polycarpa

High amounts of polyunsaturated fatty acids (PUFAs) in vegetable oil are not desirable for biodiesel or food oil due to their lower oxidative stability. The oil from Idesia polycarpa fruit contains 65⁻80% (mol%) linoleic acid (C18:2). Therefore, development of Idesia polycarpa cultivars with low PUFAs is highly desirable for Idesia polycarpa oil quality. Fatty acid desaturase 2 (FAD2) is the key enzyme converting oleic acid (C18:1) to C18:2. We isolated four FAD2 homologs from the fruit of Idesia polycarpa. Yeast transformed with IpFAD2-1, IpFAD2-2 and IpFAD2-3 can generate appreciable amounts of hexadecadienoic acid (C16:2) and C18:2, which are not present in wild-type yeast cells, revealing that the proteins encoded by these genes have Δ12 desaturase activity. Only trace amounts of C18:2 and little C16:2 were detected in yeast cells transformed with IpFAD2-4, suggesting IpFAD2-4 displays low activity. We also analyzed the activity of several FAD2 natural variants of Idesia polycarpa in yeast and found that a highly conserved Gly376 substitution caused the markedly reduced products catalyzed by IpFAD2-3. This glycine is also essential for the activity of IpFAD2-1 and IpFAD2-2, but its replacement in other plant FAD2 proteins displays different effects on the desaturase activity, suggesting its distinct roles across plant FAD2s proteins.

The FAD2 Gene in Plants: Occurrence, Regulation, and Role

Vegetable oils rich in oleic acid are more desirable than oils rich in polyunsaturated and saturated fatty acids. The biological switch of oleic acid to linoleic acid is facilitated by fatty acid desaturase 2 enzyme that is further classified into FAD2-1, FAD2-2, FAD2-3, and FAD2-4. The genes coding these enzymes have high sequence similarity, but differ mostly in their expression patterns. The seed-type FAD2 genes had evolved independently after segregation by duplication from constitutively expressed FAD2 genes. Temperature, light and wounding effectively regulate FAD2 expression in plants. FAD2 genes are expressed differently in different tissues of the plant, and the over-expression of FAD2 modifies physiological and vegetative characteristics. The activity of FAD2 leads to an increase in the content of dienoic fatty acids, and hence increases the resistance toward cold and salt stress. The thorough study of the FAD2 gene is important for understanding the expression, regulation and mechanism that will help in improving the quality of oil and stress resistance in plants.