The overexpression of rice ACYL‐CoA‐BINDING PROTEIN2 increases grain size and bran oil content in transgenic rice

Summary As Oryza sativa (rice) seeds represent food for over three billion people worldwide, the identification of genes that enhance grain size and composition is much desired. Past reports have indicated that Arabidopsis thaliana acyl‐CoA‐binding proteins ( ACBP s) are important in seed development but did not affect seed size. Herein, rice Os ACBP 2 was demonstrated not only to play a role in seed development and germination, but also to influence grain size. Os ACBP 2 mRNA accumulated in embryos and endosperm of germinating seeds in qRT ‐ PCR analysis, while β‐glucuronidase ( GUS ) assays on Os ACBP 2pro:: GUS rice transformants showed GUS expression in embryos, as well as the scutellum and aleurone layer of germinating seeds. Deletion analysis of the Os ACBP 2 5’‐flanking region revealed five copies of the seed cis‐ element, Skn‐I‐like motif (−1486/−1482, −956/−952, −939/−935, −826/−822, and −766/−762), and the removal of any adversely affected expression in seeds, thereby providing a molecular basis for Os ACBP 2 expression in seeds. When Os ACBP 2 function was investigated using osacbp2 mutants and transgenic rice overexpressing Os ACBP 2 (Os ACBP 2‐ OE ), osacbp2 was retarded in germination, while Os ACBP 2‐ OE s performed better than the wild‐type and vector‐transformed controls, in germination, seedling growth, grain size and grain weight. Transmission electron microscopy of Os ACBP 2‐ OE mature seeds revealed an accumulation of oil bodies in the scutellum cells, while confocal laser scanning microscopy indicated oil accumulation in Os ACBP 2‐ OE aleurone tissues. Correspondingly, Os ACBP 2‐ OE seeds showed gain in triacylglycerols and long‐chain fatty acids over the vector‐transformed control. As dietary rice bran contains beneficial bioactive components, Os ACBP 2 appears to be a promising candidate for enriching seed nutritional value.