A New SNP in AGPL2, Associated with Floury Endosperm in Rice, Is Identified Using a Modified MutMap Method

The floury endosperm mutants of rice can not only be used to uncover the molecular mechanisms involved in regulating starch synthesis and grain development but are also suitable for dry milling to produce rice flour of good quality. In this study, we identified and characterized a rice floury endosperm mutant, M10, from a mutant pool induced by EMS. The total starch content in the M10 seeds significantly decreased, while the soluble sugar content demonstrably increased. The grain hardness of M10 was lower than that of the wild type because of the spherical and loosely packed starch granules. The modified MutMap analysis demonstrated that AGPL2 on chromosome 1 is most likely to be the candidate gene causing a floury endosperm. The genome sequences of AGPL2 in M10 carried a single nucleotide substitution of guanine (G) to adenine (A) in the seventh exon, leading to a missense mutation from glycine (Gly) to glutamic acid (Glu) at the 251st amino acid. Allele test confirmed that AGPL2 is the gene responsible for the M10 phenotype. Both transcriptional and protein levels of AGPL2 in M10 were obviously higher than those in the developing endosperm of wild type, indicating a positive feedback regulation is caused by AGPL2 mutation. Together, our results suggest that AGPL2 plays a critical role in starch synthesis and that the modified MutMap method is feasible for identifying floury endosperm mutant genes in rice.

Automated summary

The rice floury endosperm mutant M10 was identified and characterized, showing decreased total starch content and increased soluble sugar content. The mutated AGPL2 gene on chromosome 1 was found to be responsible for the floury endosperm phenotype. The AGPL2 mutation led to higher transcriptional and protein levels and a positive feedback regulation in M10. Overall, AGPL2 plays a critical role in starch synthesis and the MutMap method is effective for identifying floury endosperm mutant genes in rice.