High-precision genome sequences and various molecular markers have allowed mapping and identification of hundreds of QTLs

associated with grain traits in rice (http://www.gramene.org/). Many QTLs have been identified from different rice germplasms by a map-based cloning approach and these accomplishments imply the promise to help understand the molecular mechanisms underlying seed development and find ways to improve rice yield. GS3, a major QTL for grain weight and length with a minor role in grain width and thickness, was recently fine mapped to a genomic region of 7.9 kb on chromosome 3 using 5,740 BC3F2 plants [4]. GS3 selleck chemicals encodes a putative transmembrane protein composed of four domains, and each functions differently in regulating grain size [5]. Sequence analyses showed that large grains are due to an early stop codon from a substitution in the second exon and, suggesting that GS3 functions as a negative regulator of grain size. Similarly, loss of GS3 leads to grain enlargement, which is true for GW2 [6], qSW5 [7] and TGW6 [8]. The major QTL for thousand-grain weight, TGW6, is mapped on chromosome 6 and encodes a novel

protein with indole-3-acetic acid (IAA)-glucose hydrolase activity. Deletion of 1-bp in TGW6 exon results in a premature stop codon to prevent the production of Torin 1 in vivo the mature protein. It has been shown that function loss of the TGW6 allele results in simultaneous increase of grain weight

and yield [8]. Furthermore, GS5 is a recently cloned QTL, Doxorubicin nmr which variation is associated with grain size diversity in rice, thus may be useful in improving yield in rice and, potentially, other crops [9]. Its spatial expression patterns demonstrate that higher expression of GS5 results in larger grains, suggesting that GS5 is a positive regulator of grain size [9]. Another QTL affecting grain width and yield, GW8, encodes a protein to positively regulate grain size. The GW8 function on grain is attributable to a critical deletion polymorphism in the promoter region. In contrast, a loss-of-function mutation brings about a better quality of appearance [10]. In this study, we report the identification and fine mapping of GS2 candidate gene. Our results demonstrated that GS2 was a novel gene involved in the regulation of grain length and width in rice. The identification and functional characterization of GS2 will help breed high-yield rice varieties and understand the underlying molecular mechanisms to control grain shape in rice and other crops. Big-grain rice line CDL was crossed with a medium-grain line R1126. The resultant F1 plants were selfed to yield a F2 population of 1000 individuals, and the following recombined inbred lines (RIL). A differentiation of grain shape was observed in RIL28 line of F6, indicating heterozygous. The individual plants of RIL28 were selfed to generate a F7 population.