Abstract
Rice bran, a by-product after milling, is a rich source of phytonutrients like oryzanols, tocopherols, tocotrienols, phytosterols, and dietary fibers. Moreover, exceptional properties of the rice bran oil make it unparalleled to other vegetable oils. However, a lipolytic enzyme Phospholipase D alpha1 (OsPLDα1) causes rancidity and ‘stale flavor’ in the oil, and thus limits the rice bran usage for human consumption. To improve the rice bran quality, sequence based allele mining at OsPLDα1 locus (3.6 Kb) was performed across 48 accessions representing 11 wild Oryza species, 8 accessions of African cultivated rice, and 7 Oryza sativa cultivars. From comparative sequence analysis, 216 SNPs and 30 InDels were detected at the OsPLDα1 locus. Phylogenetic analysis revealed 20 OsPLDα1 cDNA variants which further translated into 12 protein variants. The O. officinalis protein variant, when compared to Nipponbare, showed maximum variability comprising 22 amino acid substitutions and absence of two peptides and two β-sheets. Further, expression profiling indicated significant differences in transcript abundance within as well as between the OsPLDα1 variants. Also, a new OsPLDα1 transcript variant having third exon missing in it, Os01t0172400-06, has been revealed. An O. officinalis accession (IRGC101152) had lowest gene expression which suggests the presence of novel allele, named as OsPLDα1-1a (GenBank accession no. MF966931). The identified novel allele could be further deployed in the breeding programs to overcome rice bran rancidity in elite cultivars.
Highlights
Rice (Oryza sativa L.) bran, a by-product after milling, is composed of pericarp, aleurone, seed coat, nucellus along with the germ and a small portion of endosperm[1,2]
Across all the selected wild species accessions and cultivars, maximum number of single nucleotide polymorphism (SNPs) (73) were present in the species belonging to the O. officinalis complex (O. officinalis, O. australiensis, O. punctata, O. minuta, and O. latifolia)
Of the total SNPs identified in O. officinalis complex, a few SNPs were observed in the two AA genome species viz. O. meridionalis (T1135C, T1153C, T1207C, C1156T, A1747, A2099T, A2855G, and C1810T) and O. longistaminata (A1639G, A1747G, A2099T, and A2855G)
Summary
Rice (Oryza sativa L.) bran, a by-product after milling, is composed of pericarp, aleurone, seed coat, nucellus along with the germ and a small portion of endosperm[1,2] It constitutes about 10% of the weight of rough rice, and is comprised of 12–23% oil, 14–16% protein, and 8–10% crude fibre. Lipoxygenases act on the FFAs which contain a 1, 4-pentadiene structure, such as linoleic and linolenic acids, and lead to their conversion into low molecular-weight volatile products which cause a stale flavor in the product[14,15] It has been revealed by the the earlier studies that PLD acts as a trigger for the initiation of lipid decomposition which further leads to deterioration of the rice grain and rice bran fractions. Validation of the identified OsPLDα1 allelic variants was conducted using quantitative reverse-transcription expression analysis
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