title: Detection of Novel QTLs Regulating Grain Size in Extra-Large Grain Rice (Oryza sativa L.) Lines.
abstract: BACKGROUND
  Grain size is an important trait that affects rice yield. Although many genes that contribute to grain size have been cloned from mutants or by quantitative trait locus (QTL) analysis based on bi-parental mapping, the molecular mechanisms underlying grain-size determination remain poorly understood. In this study, we identified the lines with the largest grain size and detected novel QTLs affecting the grain size.
  
  
  RESULTS
  We screened the National Institute for Agrobiological Sciences Genebank database and identified two rice lines, BG23 with the widest grain and LG10 with the longest grain. Using these two lines, we performed QTL analysis for grain size. Eight QTLs were detected during the QTL analyses using F2 populations derived from crosses between the large-grain lines BG23 or LG10 and the middle-size grain cultivars Nipponbare and Kasalath. Both BG23 and LG10 possessed large-grain alleles of four major QTLs: GW2, GS3, qSW5/GW5, and GW8. Other three minor QTLs were derived from BG23. However, these QTLs did not explain the differences in grain size between these two lines. Additionally, four QTLs for grain length or width were detected in an F2 population derived from a cross between BG23 and LG10; this population lacked the strong effects of the four major QTLs shared by both parent plants. Of these newly detected QTLs, the effects of two QTLs, GL3b and GL6, were confirmed by progeny testing. Comparison of the length of inner epidermal cells in plants homozygous for BG23 and LG10 alleles indicated that GL3b and GL6 genes regulate cell elongation and cell division, respectively.
  
  
  CONCLUSIONS
  In this study, we detected 12 loci including 14 QTLs regulating grain size from two lines with largest grains available in Japanese stock. Of these loci, we confirmed the effect of two gene loci and mapped their candidate region. Identification of novel genes regulating grain size will contribute to our understanding of the molecular mechanisms controlling grain size.
authors.affiliation: Fukui Prefectural University, Faculty of Biotechnology, 4-1-1 Kenjojima, Matsuoka, Eiheiji-cho, Yoshida-gun, Fukui, 910-1195, Japan.|Japan Society for the Promotion of Science, Chiyoda-ku, Tokyo, 102-8472, Japan.
authors.forename: Shuhei
authors.initials: S
authors.lastname: Segami
authors.affiliation: Fukui Prefectural University, Faculty of Biotechnology, 4-1-1 Kenjojima, Matsuoka, Eiheiji-cho, Yoshida-gun, Fukui, 910-1195, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: Fukui Prefectural University, Faculty of Biotechnology, 4-1-1 Kenjojima, Matsuoka, Eiheiji-cho, Yoshida-gun, Fukui, 910-1195, Japan.
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Oki
authors.affiliation: Bioscience and Biotechnology Center, Nagoya University, Furo-cho, Chikusa, Nagoya, Aichi, 464-8601, Japan.
authors.forename: Tomonori
authors.initials: T
authors.lastname: Noda
authors.affiliation: Agrogenomics Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kanamori
authors.affiliation: Agrogenomics Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Harumi
authors.initials: H
authors.lastname: Sasaki
authors.affiliation: Agrogenomics Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Satomi
authors.initials: S
authors.lastname: Mori
authors.affiliation: Bioscience and Biotechnology Center, Nagoya University, Furo-cho, Chikusa, Nagoya, Aichi, 464-8601, Japan.
authors.forename: Motoyuki
authors.initials: M
authors.lastname: Ashikari
authors.affiliation: Bioscience and Biotechnology Center, Nagoya University, Furo-cho, Chikusa, Nagoya, Aichi, 464-8601, Japan.
authors.forename: Hidemi
authors.initials: H
authors.lastname: Kitano
authors.affiliation: Agrogenomics Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki, 305-8602, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Katayose
authors.affiliation: Fukui Prefectural University, Faculty of Biotechnology, 4-1-1 Kenjojima, Matsuoka, Eiheiji-cho, Yoshida-gun, Fukui, 910-1195, Japan. iwasaki@fpu.ac.jp.
authors.forename: Yukimoto
authors.initials: Y
authors.lastname: Iwasaki
authors.affiliation: Fukui Prefectural University, Faculty of Biotechnology, 4-1-1 Kenjojima, Matsuoka, Eiheiji-cho, Yoshida-gun, Fukui, 910-1195, Japan. miura-k@fpu.ac.jp.
authors.forename: Kotaro
authors.initials: K
authors.lastname: Miura
keywords: Grain size; QTL; Rice (Oryza sativa L.)