Plant Physiology Preview
Published on September 12, 2008; 10.1104/pp.108.125542
Received July 7, 2008
Accepted September 5, 2008
Ehd2, a rice ortholog of the maize ID1 gene, promotes flowering by upregulating Ehd1
Kazuki Matsubara , Utako Yamanouchi , Zi-Xuan Wang , Yuzo Minobe , Takeshi Izawa , and Masahiro Yano *
National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan; Plant Genome Center, Tsukuba, Ibaraki 305-0856, Japan
* Corresponding author; email: myano{at}affrc.go.jp.
Recent research into the flowering of rice (Oryza sativa) has revealed both unique and conserved genetic pathways in the photoperiodic control of flowering, compared with those in Arabidopsis thaliana. We discovered an early heading date 2 (ehd2) mutant that shows extremely late flowering under both short- and long-day conditions in a line with a background deficient in Heading date 1 (Hd1), a rice CONSTANS ortholog that belongs to the conserved pathway. This phenotype in the ehd2 mutants suggests that Ehd2 is pivotal for the floral transition in rice. Map-based cloning revealed that Ehd2 encodes a putative transcription factor with zinc finger motifs, orthologous to the INDETERMINATE1 (ID1) gene, which promotes flowering in maize (Zea mays). Ehd2 mRNA in rice tissues accumulated most abundantly in developing leaves, but was present at very low levels around the shoot apex and in roots, patterns that are similar to those of ID1. To assign the position of Ehd2 within the flowering pathway of rice, we compared transcript levels of previously isolated flowering-time genes, such as Early heading date 1 (Ehd1, a member of the unique pathway), Hd3a, and Rice FT-like 1 (RFT1) (rice florigens), between the wild-type plants and the ehd2 mutants. Severely reduced expression of these genes in ehd2 under both short- and long-day conditions suggests that Ehd2 acts as a flowering promoter mainly by upregulating Ehd1, and by upregulating the downstream Hd3a and RFT1 genes in the unique genetic network of photoperiodic flowering in rice.
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