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Grain shape in rice is a key determinant of grain appearance, yield and market value, and thus has been widely studied. Rice mutant lines with long-grain phenotypes were previously isolated from an M2 population derived from mutagenized mature pollen grains that were treated with gamma-ray irradiation for a cultivar Ma85. To understand the genetic basis underlying the long-grain trait, two mutant lines, JF171 and JF178, were crossed with the short-grain parents JF222 and Samba, generating three F2 populations. Molecular marker-based genetic analysis was employed to detect the major QTLs that affected grain length, grain width, length-to-width ratio and grain weight. Based on the data obtained for the three populations, a joint major QTL for grain length was mapped to a 4.7 Mb region between the SSR makers RM263 and RM318 on the long arm of chromosome 2. The results suggested that the two independent mutations contained in JF171 and JF178 are likely due to alterations in the same genetic region. Furthermore, we developed a BC2F2 population using JF178 and Samba and narrowed the region to 0.6 Mb. The results of the current study will be helpful to reveal the genetic basis of the above long-grain mutant lines. In general, our results provide solid genetic data to identify the unknown gene that affects grain length by map-based cloning and practice marker-assisted breeding for long-grain rice cultivars. [ABSTRACT FROM AUTHOR]

Some outer floral organs are unique in gramineous plants, like the sterile lemma and rudimentary glume in rice. However, their development mechanisms are still poorly understood. In this study, we used 4 mutants with long sterile lemma (LSL), named JF11, JF12, JF13 and JNY-7, to be crossed with Aijiaonante (AJNT) and Nipponbare (NIP), respectively. Genetic analysis indicated that LSL trait exhibited recessive heredity and was controlled by a common allele named sl-1(t). Using the method of bulk segregant analysis and linkage analysis between SSR markers and LSL trait based on F2 populations, the sl-1(t) gene was located at the interval between RM20903 and RM20948 on chromosome 7. The interval harbors a known G1 gene, which regulates the sterile lemma trait. The findings of allelic sequencing showed an 11-base deletion in gene G1 happened in the mutants of JF11, JF12 and JF13, which led to a frame-shifting mutation, whereas the mutant of JNY-7 had a base substitution that caused the change of the amino acid residue. Eight substitutions in the ORF and 10 in the upstream region from -1 to -824 were found between Indica and Japonica rice by DNA sequence analysis, but those polymorphisms have no effect on the gene function. In conclusion, we fine mapped the LSL gene, sl-1(t), and found 2 kinds of mutant alleles conferring the gene function and the DNA polymorphisms of G1 between Indica and Japonica rice. [ABSTRACT FROM AUTHOR]

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