Control of grain protein contents through SEMIDWARF1 mutant alleles: sd1 increases the grain protein content in Dee-geo-woo-gen but not in Reimei

A new possibility for genetic control of the protein content of rice grains was suggested by the allele differences of the SEMIDWARF1 ( SD1 ) mutation. Two quantitative trait loci— qPROT1 and qPROT12 —were found on chromosomes 1 and 12, respectively, using backcrossed inbred lines of Sasanishiki/Habataki//Sasanishiki///Sasanishiki. One of them, qPROT1, increased almost all grain proteins instead of only certain proteins in the recessive Habataki allele. Fine mapping of qPROT1 revealed that two gene candidates—Os01g0883800 and Os01g0883900—were included in this region. Os01g0883800 encoded Gibberellin 20 oxidase 2 as well as SD1 , the dwarf gene used in the so-called ‘Green Revolution’. Mutant analyses as well as sequencing analysis using the semi-dwarf mutant cultivars Dee-geo-woo-gen and Calrose 76 revealed that the sd1 mutant showed significantly higher grain protein contents than their corresponding wild-type cultivars, strongly suggesting that the high protein contents were caused by sd1 mutation. However, the sd1 mutant Reimei did not have high grain protein contents. It is possible to control the grain protein content and column length separately by selecting for sd1 alleles. From this finding, the genetic control of grain protein content, as well as the column length of rice cultivars, might be possible. This ability might be useful to improve rice nutrition, particularly in areas where the introduction of semi-dwarf cultivars is not advanced.