Phenotypic and Candidate Gene Analysis of a New Floury Endosperm Mutant (osagpl2-3) in Rice

A floury endosperm mutant, osagpl2-3, was isolated from the M-2 generation of japonica rice cultivar Nipponbare following ethyl methane sulfonate mutagenesis. The osagpl2-3 mutant produced a white-core endosperm compared to the transparent endosperm of the wild type (WT). The results from scanning electron microscope showed that the osagpl2-3 mutant grains comprised of round and loosely packed starch granules, some of which were compounded. The analysis for cooking and nutrition quality traits indicated that the values of gel consistency, gelatinization temperature, and rapid viscosity analysis profile of osagpl2-3 grains were lower than those of the WT. Besides, the protein content, the contents of nine different amino acids, and the thermodynamic parameters of T (p) and Delta T (1/2) in osagpl2-3 were also different from those of the WT. Genetic analysis revealed that osagpl2-3 mutation was controlled by a single recessive gene. The osagpl2-3 gene was mapped between InDel markers R1M30 and ID1-12 on rice chromosome 1. In the candidate region of the Nipponbare genome, an annotated gene, LOC_Os01g44220 which encodes a large subunit of putative ADP-glucose pyrophosphrylase named OsAPL2 was considered the optimal candidate. Cloning and sequencing of LOC_Os01g44220 in different plants of the osagpl2-3 mutants revealed a single nucleotide mutation (G -> A) in the open reading frame region, which led to a substitution of an acidic amino acid Glu (E) by a basic amino acid Lys (K) accordingly. Furthermore, the mutant site is close to the functional domain which interacts with the ADP-Glc. In brief, these results suggested that the osagpl2-3 is a new mutant of OsAPL2.