Ehd3, encoding a plant homeodomain finger-containing protein, is a critical promoter of rice flowering.

Oryza sativa (rice) flowers in response to photoperiod, and is a facultative short-day (SD) plant. Under SD conditions, flowering is promoted through the activation of FT-like genes (rice florigens) by Heading date 1 (Hd1, a rice CONSTANS homolog) and Early heading date 1 (Ehd1, with no ortholog in the Arabidopsis genome). On the other hand, under long-day (LD) conditions, flowering is delayed by the repressive function of Hd1 on FT-like genes and by downregulation of Ehd1 by the flowering repressor Ghd7 - a unique pathway in rice. We report here that an early heading date 3 (ehd3) mutant flowered later than wild-type plants, particularly under LD conditions, regardless of the Hd1-deficient background. Map-based cloning revealed that Ehd3 encodes a nuclear protein that contains a putative transcriptional regulator with two plant homeodomain (PHD) finger motifs. To identify the role of Ehd3 within the gene regulatory network for rice flowering, we compared the transcript levels of genes related to rice flowering in wild-type plants and ehd3 mutants. Increased transcription of Ghd7 under LD conditions and reduced transcription of downstream Ehd1 and FT-like genes in the ehd3 mutants suggested that Ehd3 normally functions as an LD downregulator of Ghd7 in floral induction. Furthermore, Ehd3 ghd7 plants flowered earlier and show higher Ehd1 transcript levels than ehd3 ghd7 plants, suggesting a Ghd7-independent role of Ehd3 in the upregulation of Ehd1. Our results demonstrate that the PHD-finger gene Ehd3 acts as a promoter in the unique genetic pathway responsible for photoperiodic flowering in rice.

[1]  L. Holm,et al.  The Pfam protein families database , 2011, Nucleic Acids Res..

[2]  M. Yano,et al.  A pair of floral regulators sets critical day length for Hd3a florigen expression in rice , 2010, Nature Genetics.

[3]  S. Yokoi,et al.  A gene network for long-day flowering activates RFT1 encoding a mobile flowering signal in rice , 2009, Development.

[4]  S. Park,et al.  OsMADS50 and OsMADS56 function antagonistically in regulating long day (LD)-dependent flowering in rice. , 2009, Plant, cell & environment.

[5]  V. Irish.  Evolution of petal identity. , 2009, Journal of experimental botany.

[6]  B. Trevaskis,et al.  The molecular biology of seasonal flowering-responses in Arabidopsis and the cereals. , 2009, Annals of botany.

[7]  Kosuke M. Teshima,et al.  Variations in Hd1 proteins, Hd3a promoters, and Ehd1 expression levels contribute to diversity of flowering time in cultivated rice , 2009, Proceedings of the National Academy of Sciences.

[8]  E. Davidson,et al.  The evolution of hierarchical gene regulatory networks , 2009, Nature Reviews Genetics.

[9]  Y. Xuan,et al.  Rice Indeterminate 1 (OsId1) is necessary for the expression of Ehd1 (Early heading date 1) regardless of photoperiod. , 2008, The Plant journal : for cell and molecular biology.

[10]  J. Dubcovsky,et al.  Genetic and Molecular Characterization of the VRN2 Loci in Tetraploid Wheat1[W][OA] , 2008, Plant Physiology.

[11]  Alexandra M. E. Jones,et al.  A PHD-Polycomb Repressive Complex 2 triggers the epigenetic silencing of FLC during vernalization , 2008, Proceedings of the National Academy of Sciences.

[12]  M. Yano,et al.  Ehd2, a Rice Ortholog of the Maize INDETERMINATE1 Gene, Promotes Flowering by Up-Regulating Ehd11[C][W] , 2008, Plant Physiology.

[13]  Qifa Zhang,et al.  RID1, encoding a Cys2/His2-type zinc finger transcription factor, acts as a master switch from vegetative to floral development in rice , 2008, Proceedings of the National Academy of Sciences.

[14]  Lei Wang,et al.  Natural variation in Ghd7 is an important regulator of heading date and yield potential in rice , 2008, Nature Genetics.

[15]  F. Turck,et al.  Regulation and identity of florigen: FLOWERING LOCUS T moves center stage. , 2008, Annual review of plant biology.

[16]  Shojiro Tamaki,et al.  Hd3a and RFT1 are essential for flowering in rice , 2008, Development.

[17]  S. Lin,et al.  Detection of quantitative trait loci controlling extremely early heading in rice , 2008, Theoretical and Applied Genetics.

[18]  D. Weigel,et al.  Move on up, it's time for change--mobile signals controlling photoperiod-dependent flowering. , 2007, Genes & development.

[19]  T. Izawa,et al.  Adaptation of flowering-time by natural and artificial selection in Arabidopsis and rice. , 2007, Journal of experimental botany.

[20]  M. Nei,et al.  MEGA4: Molecular Evolutionary Genetics Analysis (MEGA) software version 4.0. , 2007, Molecular biology and evolution.

[21]  Shoichi Matsuo,et al.  Hd3a Protein Is a Mobile Flowering Signal in Rice , 2007, Science.

[22]  J. Dubcovsky,et al.  Wheat VIN3-like PHD finger genes are up-regulated by vernalization , 2007, Molecular Genetics and Genomics.

[23]  C. Dean,et al.  The PHD Finger Protein VRN5 Functions in the Epigenetic Silencing of Arabidopsis FLC , 2007, Current Biology.

[24]  Robert J. Schmitz,et al.  A PHD finger protein involved in both the vernalization and photoperiod pathways in Arabidopsis. , 2006, Genes & development.

[25]  S. Kay,et al.  Photoperiodic control of flowering: not only by coincidence. , 2006, Trends in plant science.

[26]  M. Robertson,et al.  The Arabidopsis thaliana vernalization response requires a polycomb-like protein complex that also includes VERNALIZATION INSENSITIVE 3 , 2006, Proceedings of the National Academy of Sciences.

[27]  S. Oka,et al.  Early infection of scutellum tissue with Agrobacterium allows high-speed transformation of rice. , 2006, The Plant journal : for cell and molecular biology.

[28]  Anjanabha Saha,et al.  ING2 PHD domain links histone H3 lysine 4 methylation to active gene repression , 2006, Nature.

[29]  Thomas A. Milne,et al.  A PHD finger of NURF couples histone H3 lysine 4 trimethylation with chromatin remodelling , 2006, Nature.

[30]  V. Verkhusha,et al.  Molecular mechanism of histone H3K4me3 recognition by plant homeodomain of ING2 , 2006, Nature.

[31]  B. Trevaskis,et al.  HvVRN2 Responds to Daylength, whereas HvVRN1 Is Regulated by Vernalization and Developmental Status1 , 2006, Plant Physiology.

[32]  T. Ishizuka,et al.  Distinct and Cooperative Functions of Phytochromes A, B, and C in the Control of Deetiolation and Flowering in Rice[W][OA] , 2005, The Plant Cell Online.

[33]  안진흥.  Functional analyses of the flowering time gene OsMADS50, the putagive SUPPRESSOR OF OVEREXPRESSION OF CO 1/AGAMOUS-LIKE 20 (SOC1/AGL20) ortholog in rice , 2004 .

[34]  G. Coupland,et al.  The Molecular Basis of Diversity in the Photoperiodic Flowering Responses of Arabidopsis and Rice , 2004, Plant Physiology.

[35]  Kazuyuki Doi,et al.  Ehd1, a B-type response regulator in rice, confers short-day promotion of flowering and controls FT-like gene expression independently of Hd1. , 2004, Genes & development.

[36]  J. Bennetzen,et al.  The Wheat VRN2 Gene Is a Flowering Repressor Down-Regulated by Vernalization , 2004, Science.

[37]  R. Amasino,et al.  Vernalization in Arabidopsis thaliana is mediated by the PHD finger protein VIN3 , 2004, Nature.

[38]  G. Simpson.  Evolution of flowering in response to day length: flipping the CONSTANS switch. , 2003, BioEssays : news and reviews in molecular, cellular and developmental biology.

[39]  G. Coupland,et al.  EARLY BOLTING IN SHORT DAYS Is Related to Chromatin Remodeling Factors and Regulates Flowering in Arabidopsis by Repressing FT Article, publication date, and citation information can be found at www.plantcell.org/cgi/doi/10.1105/tpc.012153. , 2003, The Plant Cell Online.

[40]  M. Yano,et al.  Adaptation of photoperiodic control pathways produces short-day flowering in rice , 2003, Nature.

[41]  M. Yano,et al.  Comparative biology comes into bloom: genomic and genetic comparison of flowering pathways in rice and Arabidopsis. , 2003, Current opinion in plant biology.

[42]  Takashi Araki,et al.  Hd3a, a rice ortholog of the Arabidopsis FT gene, promotes transition to flowering downstream of Hd1 under short-day conditions. , 2002, Plant & cell physiology.

[43]  M. Yano,et al.  Phytochrome mediates the external light signal to repress FT orthologs in photoperiodic flowering of rice. , 2002, Genes & development.

[44]  M. Yano,et al.  Genetic control of flowering time in rice, a short-day plant. , 2001, Plant physiology.

[45]  M. Yano,et al.  Ti-Plasmid Vectors Useful for Functional Analysis of Rice Genes , 2001 .

[46]  J. Franco-Zorrilla,et al.  early bolting in short days: An Arabidopsis Mutation That Causes Early Flowering and Partially Suppresses the Floral Phenotype of leafy , 2001, Plant Cell.

[47]  M. Yano,et al.  Hd1, a Major Photoperiod Sensitivity Quantitative Trait Locus in Rice, Is Closely Related to the Arabidopsis Flowering Time Gene CONSTANS , 2000, Plant Cell.

[48]  H. Kitano,et al.  A Recessive Heterochronic Mutation, plastochron1, Shortens the Plastochron and Elongates the Vegetative Phase in Rice , 1998, Plant Cell.

[49]  J. Seemann,et al.  An efficient method for isolation of RNA from tissue cultured plant cells. , 1991, Nucleic acids research.

[50]  R. Laskey,et al.  Two interdependent basic domains in nucleoplasmin nuclear targeting sequence: Identification of a class of bipartite nuclear targeting sequence , 1991, Cell.

[51]  N. Saitou,et al.  The neighbor-joining method: a new method for reconstructing phylogenetic trees. , 1987, Molecular biology and evolution.