OsCOL4 is a constitutive flowering repressor upstream of Ehd1 and downstream of OsphyB.
Plants recognize environmental factors to determine flowering time. CONSTANS (CO) plays a central role in the photoperiod flowering pathway of Arabidopsis, and CO protein stability is modulated by photoreceptors. In rice, Hd1, an ortholog of CO, acts as a flowering promoter, and phytochromes repress Hd1 expression. Here, we investigated the functioning of OsCOL4, a member of the CONSTANS-like (COL) family in rice. OsCOL4 null mutants flowered early under short or long days. In contrast, OsCOL4 activation-tagging mutants (OsCOL4-D) flowered late in either environment. Transcripts of Ehd1, Hd3a, and RFT1 were increased in the oscol4 mutants, but reduced in the OsCOL4-D mutants. This finding indicates that OsCOL4 is a constitutive repressor functioning upstream of Ehd1. By comparison, levels of Hd1, OsID1, OsMADS50, OsMADS51, and OsMADS56 transcripts were not significantly changed in oscol4 or OsCOL4-D, suggesting that OsCOL4 functions independently from previously reported flowering pathways. In osphyB mutants, OsCOL4 expression was decreased and osphyB oscol4 double mutants flowered at the same time as the osphyB single mutants, indicating OsCOL4 functions downstream of OsphyB. We also present evidence for two independent pathways through which OsPhyB controls flowering time. These pathways are: (i) night break-sensitive, which does not need OsCOL4; and (ii) night break-insensitive, in which OsCOL4 functions between OsphyB and Ehd1.
Lee
Yang-Seok
YS
Department of Life Science, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Korea.
Jeong
Dong-Hoon
DH
Lee
Dong-Yeon
DY
Yi
Jakyung
J
Ryu
Choong-Hwan
CH
Kim
Song L
SL
Jeong
Hee J
HJ
Choi
Sang C
SC
Jin
Ping
P
Yang
Jungil
J
Cho
Lae-Hyeon
LH
Choi
Heebak
H
An
Gynheung
G
D004269:DNA, Bacterial / Q000235:genetics; D035264:Flowers / Q000254:growth & development*; D018506:Gene Expression Regulation, Plant; D016254:Mutagenesis, Insertional; D009154:Mutation; D012275:Oryza / Q000235:genetics* / Q000378:metabolism; D017440:Photoperiod; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018749:RNA, Plant / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism
D004269:DNA, Bacterial; D010940:Plant Proteins; D018749:RNA, Plant; D012097:Repressor Proteins; C036483:T-DNA