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Rice (Oryza Sativa L.) Whole Grain Genome-Wide Association Study for Neutral Sugar Content


 Background Cell wall matrix polysaccharides are structurally complex and diverse, but our knowledge about their synthesis is limited. The building blocks (monosaccharides) of these polysaccharides have critical role in defining the number and the ultrastructure (size) of rice grains, and therefore would have great influence on seed vigor, yield and quality. Genome-wide association study (GWAS) is a method of choice for fine mapping of QTLs involved in defining plant cell wall structure and modifications. The monosaccharides that contribute to major cell wall matrix polysaccharides in whole grains of 197 rice accessions were quantified using acid hydrolysis and high-performance anion-exchange chromatography with pulsed amperometric detection. A GWAS of calculated monosaccharide content in rice whole grain (RWG) was carried out using 33,812 single-nucleotide polymorphisms (SNPs) to identify corresponding markers in 200 kbp flanking regions.Results In total, 49 significant SNPs contained in 19 genomic regions (QTLs) on eight chromosomes of rice were determined to be associated with monosaccharides content. The candidate genes in QTL regions included the following: arabinose content was associated with α-N-arabinofuranosidase, pectinesterase inhibitor, a glycoside hydrolase (GH) from family 16 (GH16 enzyme); xylose content was associated with ethylene-responsive element-binding protein and a pyruvate kinase; mannose content was associated with a MYB family transcription factor and S-domain receptor-like protein kinase; galactose content was associated with a glycocyltransferase (GT) from family 8 (GT8 enzyme), GRAS family transcription factor, glutathione S-transferase, GH16 and GH17 enzymes; fucose content was associated with a GH16 enzyme, lysine-rich arabinogalactan protein 19 and a receptor protein kinase; and finally rhamnose content was associated with OsFBX41, pectinesterase, COBRA-like protein, and OsSAUR13 (Auxin-responsive SAUR).Conclusion The results of this study should improve our understanding of the genetic basis of the factors that might be involved in the biosynthesis and turnover of major matrix polysaccharides present in RWG. Several QTLs were identified on different chromosomes, all are reported for first. Further, our data provide insight that will be useful in the design of future breeding programs, allowing breeders to use available genetic resources more effectively in meeting global food demand and supply.