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Annotated Information

Hd16, a gene for casein kinase I, is involved in the control of rice flowering time by modulating the day-length response


Under long sunshine condition,Hd16 enhances its function by phosphorylation Ghd7 to down regulation Ehd1 and its downstream genes' transcription levels such as Hd3a and RFT1. At last, it lead to delay flowering. Biochemical characterization indicated that the functional Hd16 recombinant protein specifically phosphorylated Ghd7. These results demonstrate that Hd16 acts as an inhibitor in the rice flowering pathway by enhancing the photoperiod response as a result of the phosphorylation of Ghd7.[1] EL1 is a key regulatory factors involved in GA response. SLR1, one of the DELLA proteins, negatively regulates of GA signaling through phosphorylation.[3] Furthermore, expression of homeotic EL1 is negatively regulated by the transcription factors of HOX1.[2]


Hd16 is constitutively expressed. All tissues and developmental stages can be detected. GUS staining results showed that Hd16 had a higher expression level in the vascular tissue of the leaves and stems and root primordia. Map‐based cloning revealed that the rice flowering‐time quantitative trait locus (QTL) Heading date 16 (Hd16) encodes a casein kinase‐I protein.By using near‐isogenic lines with functional or deficient alleles of several rice flowering‐time genes, we observed significant digenetic interactions between Hd16 and four other flowering‐time genes (Ghd7, Hd1, DTH8 and Hd2). In a near‐isogenic line with the weak‐photoperiod‐sensitivity allele of Hd16, transcription levels of Ehd1, Hd3a, and RFT1 increased under long‐day conditions, and transcription levels of Hd3a and RFT1 decreased under short‐day conditions. Expression analysis under continuous light and dark conditions showed that Hd16 was not likely to be associated with circadian clock regulation. [1]. el1 had an enhanced GA response, consistent with the suppression of EL1 expression by exogenous GA3. [3]Overexpression of rice homeobox gene HOX1a resulted in enhanced gibberellin (GA) response, indicating a positive effect of HOX1a in GA signaling. HOX1a is induced by GA and encodes a homeobox transcription factor with transcription repression activity. In addition, HOX1a suppresses the transcription of early flowering1 (EL1), a negative regulator of GA signaling, and further electrophoretic mobility shift assay and chromatin immunoprecipitation analysis revealed that HOX1a directly bound to the promoter region of EL1 to suppress its expression and stimulate GA signaling. [2]


One non-synonymous substitution in Hd16 resulted in decreased photoperiod sensitivity in rice, and this substitution occurred naturally in an old rice cultivar.[1]

Labs working on this gene

We performed map-based cloning of a flowering-time quantitative trait locus (QTL),Heading date 16(Hd16), and revealed that Hd16encodes a casein kinase-I protein. One non-synonymous substitution in Hd16changes the photoperiod sensitivity. The functional Hd16 recombinant protein phosphorylated Ghd7in vitro. Our results suggested thatHd16is involved in the photoperiodic flowering pathway by means of its phosphorylation of Ghd7. Our findings provided evidence for a new phosphorylation-related function of Hd16/EL1 (i.e. the phosphorylation of Ghd7) in the photoperiod response pathway that controls rice flowering.


1. Kiyosumi Hori;Eri Ogiso-Tanaka;Kazuki Matsubara;Utako Yamanouchi;Kaworu Ebana;Masahiro Yano

 Hd16, a gene for casein kinase I, is involved in the control of rice flowering time by modulating the day-length response
 The Plant Journal, 2013, 76(1):36-46

2. Bi-Qing Wen;Mei-Qing Xing;Hua Zhang;Cheng Dai;Hong-Wei Xue

 Rice Homeobox Transcription Factor HOX1a Positively Regulates Gibberellin Responses by Directly Suppressing EL1
 Journal of Integrative Plant Biology, 2011, 53(11): 869-878

3. Cheng Dai;Hong-Wei Xue

 Rice early flowering1, a CKI, phosphorylates DELLA protein SLR1 to negatively regulate gibberllin signalling
 The EMBO Journal, 2010, 29(11): 1916-1927

Structured Information