OsAAP8 mutation leads to significant improvement in the nutritional quality and appearance of rice grains.

Members of the permease gene family are responsible for important biological functions in the growth and development of rice. Here, we show that OsAAP8 is a constitutive expression gene, and its translated protein is localized on the cell membrane. Mutation of the OsAAP8 can promote the expression of genes related to protein and amylopectin synthesis, and also promote the enlargement of protein bodies in its endosperm, leading to an increase in the protein, amylopectin, and total amino acid content of grains in OsAAP8 mutants. Seeds produced by the OsAAP8 mutant were larger, and the chalkiness traits of the OsAAP8 mutants were significantly reduced, thereby improving the nutritional quality and appearance of rice grains. The OsAAP8 protein is involved in the transport of various amino acids; OsAAP8 mutation significantly enhanced the root absorption of a range of amino acids and might affect the distribution of various amino acids. Therefore, OsAAP8 is an important quality trait gene with multiple biological functions, which provides important clues for the molecular design of breeding strategies for developing new high-quality varieties of rice. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-024-01473-w.

OsNAC74 affects grain protein content and various biological traits by regulating OsAAP6 expression in rice.

The grain protein content is an important quality trait in cereals, and the expression level of the OsAAP6 can significantly affect the grain protein content in rice. Through site-directed mutagenesis, we found that the position from -7 to -12 bp upstream of the transcription start site of the OsAAP6 was the functional variation site. By using the yeast single hybrid test, point-to-point in yeast, and the local surface plasmon resonance test, the OsNAC74 was screened and verified to be a regulator upstream of OsAAP6. The OsNAC74 is a constitutively expressed gene whose product is located on the cell membrane. The OsAAP6 and the genes related to the seed storage in the Osnac74 mutants were downregulated, and grain protein content was significantly reduced. In addition, OsNAC74 had a significant impact on quality traits such as grain chalkiness and gel consistency in rice. Although the Osnac74 mutant seeds were relatively small, the individual plant yield was not decreased. Therefore, OsNAC74 is an important regulatory factor with multiple biological functions. This study provides important information for the later use of OsNAC74 gene for molecular design and breeding in rice. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-023-01433-w.

OsG6PGH1 affects various grain quality traits and participates in the salt stress response of rice.

Cytoplasmic 6-phosphogluconate dehydrogenase (G6PGH) is a key enzyme in the pentose phosphate pathway that is involved in regulating various biological processes such as material metabolism, and growth and development in plants. However, it was unclear if OsG6PGH1 affected rice grain quality traits. We perform yeast one-hybrid experiments and reveal that OsG6PGH1 may interact with OsAAP6. Subsequently, yeast in vivo point-to-point experiments and local surface plasmon resonance experiments verified that OsG6PGH1 can bind to OsAAP6. OsG6PGH1 in rice is a constitutive expressed gene that may be localized in the cytoplasm. OsAAP6 and protein-synthesis metabolism-related genes are significantly upregulated in OsG6PGH1 overexpressing transgenic positive endosperm, corresponding to a significant increase in the number of protein bodies II, promoting accumulation of related storage proteins, a significant increase in grain protein content (GPC), and improved rice nutritional quality. OsG6PGH1 positively regulates amylose content, negatively regulates chalkiness rate and taste value, significantly affects grain quality traits such as appearance, cooking, and eating qualities of rice, and is involved in regulating the expression of salt stress related genes, thereby enhancing the salt-stress tolerance of rice. Therefore, OsG6PGH1 represents an important genetic resource to assist in the design of high-quality and multi-resistant rice varieties.