title: Phytochrome B regulates Heading date 1 (Hd1)-mediated expression of rice florigen Hd3a and critical day length in rice.
abstract: Many plants require circadian clock and light information for the photoperiodic control of flowering. In Arabidopsis, a long-day plant (LDP), flowering is triggered by the circadian clock-controlled expression of CONSTANS (CO) and light stabilization of the CO protein to induce FT (FLOWERING LOCUS T). In rice, a short-day plant (SDP), the CO ortholog Heading date 1 (Hd1) regulates FT ortholog Hd3a, but regulation of Hd3a by Hd1 differs from that in Arabidopsis. Here, we report that phytochrome B (phyB)-mediated suppression of Hd3a is a primary cause of long-day suppression of flowering in rice, based on the three complementary discoveries. First, overexpression of Hd1 causes a delay in flowering under SD conditions and this effect requires phyB, suggesting that light modulates Hd1 control of Hd3a transcription. Second, a single extension of day length decreases Hd3a expression proportionately with the length of daylight. Third, Hd1 protein levels in Hd1-overexpressing plants are not altered in the presence of light. These results also suggest that phyB-mediated suppression of Hd3a expression is a component of the molecular mechanism for critical day length in rice.
authors.affiliation: Laboratory of Plant Molecular Genetics, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, 630-0192, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Ishikawa
authors.forename: Mayumi
authors.initials: M
authors.lastname: Aoki
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Kurotani
authors.forename: Shuji
authors.initials: S
authors.lastname: Yokoi
authors.forename: Tomoko
authors.initials: T
authors.lastname: Shinomura
authors.forename: Makoto
authors.initials: M
authors.lastname: Takano
authors.forename: Ko
authors.initials: K
authors.lastname: Shimamoto
mesh_terms: D002940:Circadian Rhythm; D035264:Flowers; D018506:Gene Expression Regulation, Plant; D012275:Oryza / Q000502:physiology*; D017440:Photoperiod; D051939:Phytochrome B / Q000502:physiology*; D010940:Plant Proteins / Q000502:physiology*
chemical_list: D010940:Plant Proteins; D051939:Phytochrome B