Proteomic Variability and Nutrient-Related Proteins across Pigmented and Non-Pigmented Rice Grains

Rice protein is considered an important dietary protein source. Information regarding rice nutrient-related protein expression is still scarce, hence further study investigating this aspect is highly needed. Herein, we applied sequential window acquisition of all theoretical mass spectra (SWATH-MS) for a comparative proteomic analysis across six different Malaysian rice varieties. These consisted of black rice (BR: PH9 and BALI), red rice (RR: MRQ100 and MRM16), and white rice (WR: MRQ76 and MR297). This study aimed to unravel rice nutrient-related proteins and if their expressions were significantly different across varieties. A total of 4022 quantified proteins were found to be significantly expressed across all varieties with a false discovery rate (FDR) < 1% and p < 0.05. While among 1792 differentially expressed proteins (DEPs) that were identified, 74 DEPs had functions related to nutrient biosynthesis. There were significantly higher expressions of key enzymes for the carotenoid and amylopectin biosynthesis pathways and seed storage proteins, i.e., prolamins and glutelins in RR. Glycoproteins such as cupin and germin-like protein, as well as enzymes that are involved in the biosynthesis of thiamine and anthocyanin were abundantly found in BR. WR was particularly enriched with biosynthesis enzymes for essential amino acids (methionine and arginine), vitamin B, and unsaturated fatty acid. This study provides us insights into the differential expressions of storage and functional proteins with nutrient-related properties in shaping rice grain pigmentations and plant immunity, as well as in contributing diverse health benefits as daily functional food for human consumption.