Plant & Animal Genomes XIII Conference

January 15-19, 2005
Town & Country Convention Center
San Diego, CA

Genetic Control Of Flowering Time In Rice

Masahiro Yano¹ , Takeshi Izawa¹ , Utako Yamanouchi¹ , Hitoshi Nakagawa¹ , Eri Ogiso² , Kazuki Matsubara¹ , Yasunori Nonoue³ , Shin-ichi Yamamoto¹ , Takuji Sasaki¹

¹  National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan

²  Institute of Biological Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan

³  Institute of the Society for Techno-Innovation of Agriculture, Forestry and Fisheries, Tsukuba, Ibaraki 305-0854, Japan

A large amount of naturally occurring variation is observed in the photoperiodic response of flowering among rice cultivars. QTL analyses have revealed that more than 15 loci are involved in flowering time. Nearly isogenic lines have been developed by marker-assisted selection and used for the analysis of epistatic interaction among QTLs. Map-based cloning has been performed on several QTLs. We have demonstrated that Hd1 is an ortholog of CONSTANS in Arabidopsis and is involved in the promotion and inhibition of heading under short-day (SD) and long-day (LD) conditions, respectively. Hd6 is involved in inhibition under LD conditions and encodes the alpha-subunit of protein kinase CK2. Hd3a shows a high level of similarity to Arabidopsis FT and functions as a flowering inducer. Ehd1 promotes flowering mainly under SD conditions and encodes a B-type response regulator. Hd5 is involved in inhibition under LD conditions and encodes a putative subunit of a CCAAT-box-binding protein. Lhd4 is involved in inhibition under LD conditions and encodes a protein with a CCT motif. Combining information from these genetic and sequencing analyses has revealed that combinations of natural alleles with loss or gain of function at particular QTLs seem to generate a wide range of variation in photoperiodic flowering. We propose a genetic control pathway for photoperiodic flowering and have revealed the hierarchical relationship of these genes in the pathway. Comparison of molecular mechanisms between rice (an SD plant) and Arabidopsis (an LD plant) reveals evolutionarily conserved and divergent features in the photoperiodic control of flowering.