Gene Details:

Functional Descriptions:

  • Transcript levels of three flowering regulators-Ehd1, OsMADS14, and Hd3a-were decreased in these mutants, whereas those of OsGI and Hd1 were unchanged.
  • These results indicate that OsMADS51 is a flowering promoter, particularly in SDs, and that this gene functions upstream of Ehd1, OsMADS14, and Hd3a.
  • To further investigate the relationship with other flowering promoters, we generated transgenic plants in which expression of Ehd1 or OsGI was suppressed.
  • In summary, OsMADS51 is a novel flowering promoter that transmits a SD promotion signal from OsGI to Ehd1.
  • OsMADS51 is a short-day flowering promoter that functions upstream of Ehd1, OsMADS14, and Hd3a.
  • Ghd7 (Grain number, plant height and heading date 7) was acutely induced when phytochrome signals coincided with a photosensitive phase set differently by distinct photoperiods and this induction repressed Ehd1 the next morning.
  • These observations imply that OsMADS50 and OsMADS56 function antagonistically through OsLFL1-Ehd1 in regulating LD-dependent flowering.
  • Heading date gene, dth3 controlled late flowering in O. Glaberrima Steud. by down-regulating Ehd1.
  • These results provide direct evidence that phytochromes inhibit flowering by affecting both Hd1 and Ehd1 flowering pathways.
  • Early heading date1 (Ehd1), an additional rice floral activator, was also highly expressed in the s73 mutant, suggesting that SE5 represses Ehd1 in wild-type plants.
  • Since the two genes Se1 (= Hd1) and Ef1 (= Ehd1) are known to up-regulate the rice homolog of Arabidopsis FT, it is suggested that the detected epistasis may respond to diverse environments by modulating the CO/FT system conserved in flowering plants.
  • We propose that both positive (OsMADS50 and Ehd1) and negative (Hd1, phyB and Ghd7) regulators of RFT1 form a gene network that regulates LD flowering in rice.
  • Among these regulators, Ehd1, a rice-specific floral inducer, integrates multiple pathways to regulate RFT1, leading to flowering under appropriate photoperiod conditions.
  • Therefore, two key flowering time genes, Hd1 and Ehd1, can control panicle development in rice; this may affect crop yields in the field through florigen expression in leaf.
  • We further revealed that Hd1 and/or Ehd1 caused up-regulation of Terminal Flower 1-like genes and precocious expression of panicle formation-related genes at shoot apical meristems during panicle development.
  • OsCOL4 is a constitutive flowering repressor upstream of Ehd1 and downstream of OsphyB.
  • The results revealed that the combination of Heading-date 1 (Hd1) and Early heading date 1 (Ehd1) can reduce the number of primary branches in a panicle, resulting in smaller spikelet numbers per panicle; this occurs independently of the control of flowering time.
  • By regulating Ehd1, RFT1, and Hd3a, Ghd8 delayed flowering under long-day conditions, but promoted flowering under short-day conditions.
  • The comparison of the nucleotide sequences suggested that Ef1 is the same as Early heading date 1 (Ehd1).
  • 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.
  • We examined the footprints of natural and artificial selections for four major genes of the photoperiod pathway, namely PHYTOCHROME B (PhyB), HEADING DATE 1 (Hd1), HEADING DATE 3a (Hd3a), and EARLY HEADING DATE 1 (Ehd1), by investigation of the patterns of nucleotide polymorphisms in cultivated and wild rice.
  • 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).
  • The quantitative real-time PCR assay revealed that DTH8 could down-regulate the transcriptions of Ehd1 (for Early heading date1) and Hd3a (for Heading date3a; a rice ortholog of FLOWERING LOCUS T) under long-day conditions.
  • In this study, it was found that the flowering promoting gene Ehd1 and its putative downstream genes were all repressed by OsLFL1.
  • 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.
  • 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.
  • We also found that LHD1 could down-regulate the expression of several floral transition activators such as Ehd1, Hd3a and RFT1 under long-day conditions, but not under short-day conditions.
  • OsId1 regulates the expression of Ehd1 (Early heading date 1) and its downstream genes, including Hd3a (a rice ortholog of FT) and RFT1 (Rice Flowering Locus T1), under both SD and LD conditions.
  • In rice, the expression of Ehd1 is also controlled by the photoperiodic flowering genes OsGI (a rice ortholog of GI) and OsMADS51.
  • This study demonstrates that the activation of Ehd1 by OsId1 is required for the promotion of flowering.
  • In addition, OsELF3-1 is involved in blue light signaling by activating early heading date 1 (Ehd1) expression to promote rice flowering under short-day (SD) conditions.
  • Here, we report isolation and characterization of a positive regulator of Ehd1, Early heading date 4 (Ehd4).
  • Ehd1 and Hd3a can also be down-regulated by the photoperiodic flowering genes Ghd7 and Hd1 (a rice ortholog of CONSTANS).
  • Thus, two distinct gating mechanisms–of the floral promoter Ehd1 and the floral repressor Ghd7–could enable manipulation of slight differences in day length to control Hd3a transcription with a critical day-length threshold.
  • Here, we report that the rice Early heading date 1 (Ehd1) gene, which confers SD promotion of flowering in the absence of a functional allele of Hd1, encodes a B-type response regulator that might not have an ortholog in the Arabidopsis genome.
  • Ehd1 mRNA was induced by 1-wk SD treatment, and Ehd1 may promote flowering by inducing FT-like gene expression only under SD conditions.
  • Ehd1, a B-type response regulator in rice, confers short-day promotion of flowering and controls FT-like gene expression independently of Hd1.
  • As observed from osvil2, a null mutation of OsEMF2b caused late flowering by increasing OsLFL1 expression and decreasing Ehd1 expression.
  • In addition, expression of the Hd3a and Rice Flowering-locus T 1 (RFT1) florigen genes was up-regulated in leaves of the Hd1 Ehd1 line at the time of the floral transition.
  • To assign the position of Ehd2 within the flowering pathway of rice, we compared transcript levels of previously isolated flowering-time genes, such as Ehd1, a member of the unique pathway, Hd3a, and Rice FT-like1 (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 up-regulating Ehd1 and by up-regulating the downstream Hd3a and RFT1 genes in the unique genetic network of photoperiodic flowering in rice.
  • Ehd2, a rice ortholog of the maize INDETERMINATE1 gene, promotes flowering by up-regulating Ehd1.
  • We also found that the type of Hd3a promoter and the level of Ehd1 expression contribute to the diversity in flowering time and Hd3a expression level.
  • Variations in Hd1 proteins, Hd3a promoters, and Ehd1 expression levels contribute to diversity of flowering time in cultivated rice.
  • Knockdown of OsSAMS1, 2 and 3 led to distinguished late flowering and greatly reduced the expression of the flowering key genes, Early heading date 1 (Ehd1), Hd3a and RFT1 (rice FT-like genes).
  • Rice Indeterminate 1 (OsId1) is necessary for the expression of Ehd1 (Early heading date 1) regardless of photoperiod.
  • We grew four rice lines having different flowering time genotypes (hd1 Ehd1, hd1 Ehd1, Hd1 Ehd1 and Hd1 Ehd1) under distinct photoperiod conditions.
  • This indicates that LHD1 may delay flowering by repressing the expression of Ehd1, Hd3a and RFT1 under long-day conditions.
  • However, in rice, there is a unique Ehd1-dependent flowering pathway that is Hd1-independent.
  • We conclude that Ehd4 is a novel Oryza-genus-specific regulator of Ehd1, and it plays an essential role in photoperiodic control of flowering time in rice.
  • The expression of Hd3a and FTL decreased in these transgenic plants, whereas the expression of Hd1, Early heading date 1 (Ehd1), OsMADS51, and OsMADS50 did not significantly change.
  • Hd3a expression is induced by Ehd1 (Early heading date 1) expression when blue light coincides with the morning phase set by OsGIGANTEA(OsGI)-dependent circadian clocks.
  • The Early heading date 1 (Ehd1) which promotes the RFT1, was up-regulated by DTH3 in both LD and SD conditions.
  • We identified a nonfunctional RFT1 allele (rft1); the lines carrying homozygous Ehd1 and Hd3a/rft1 failed to induce the floral transition under SD and LD conditions.
  • Both Hd1 and Ehd1 are important for artificial selection of flowering time in cultivated rice.
  • Both Hd1 and Ehd1 may be important during artificial selection for flowering time, especially in a subtropical region such as Taiwan.

Literature:

Gene Resources:

Sequences:

cDNA Sequence
  • >LOC_Os10g32600.1
    ATGGCTTCAAGTGGAGACACAAATACAGTGATGAAATATGTTGCAAATGGCGCTTTTGATTTCCTGCTAAAACCTGTGAGGATCGAAGAGCTGAGCAACATTTGGCAGCACATATTCCGAAAGCAAATGCAAGATCACAAGAACAATAACATGGTTGGAAATCTCGAAAAACCCGGTCATCCTCCATCAATATTAGCCATGGCTCGTGCTACTCCGGCTACCACGAGATCAACGGCCACCGAAGCTTCGCTAGCGCCTCTAGAAAATGAGGTGAGAGATGACATGGTCAACTACAATGGCGAGATCACGGACATACGAGACCTCGGAAAGTCCAGGCTGACCTGGACCACGCAGTTGCACCGTCAGTTCATTGCAGCAGTGAACCACCTCGGAGAAGACAAGGCAGTTCCAAAGAAGATACTAGGGATAATGAAGGTCAAACATTTGACAAGAGAGCAAGTTGCCAGTCATCTGCAGGTAATATTAAATACAGGATGCAACTGAAGAAATCGATTCCAACAACAAGCAAACACGGAGCGACTTTGTCATCCACCGCTCTCGACAAAACACAAGACCACCCTTCAAGATCGCAGTATTTCAATCAAGACGGATGCAAGGAAATCATGGACTACTCTTTACCGAGAGATGACCTCTCAAGTGGCTCAGAGTGCATGCTTGAAGAACTGAACGATTACTCATCCGAAGGTTTCCAAGATTTCCGATGGGATTCAGACAAACAGGAATATGGACCATGTTTTTGGAATTTCTAG
CDS Sequence
  • >LOC_Os10g32600.1
    ATGGCTTCAAGTGGAGACACAAATACAGTGATGAAATATGTTGCAAATGGCGCTTTTGATTTCCTGCTAAAACCTGTGAGGATCGAAGAGCTGAGCAACATTTGGCAGCACATATTCCGAAAGCAAATGCAAGATCACAAGAACAATAACATGGTTGGAAATCTCGAAAAACCCGGTCATCCTCCATCAATATTAGCCATGGCTCGTGCTACTCCGGCTACCACGAGATCAACGGCCACCGAAGCTTCGCTAGCGCCTCTAGAAAATGAGGTGAGAGATGACATGGTCAACTACAATGGCGAGATCACGGACATACGAGACCTCGGAAAGTCCAGGCTGACCTGGACCACGCAGTTGCACCGTCAGTTCATTGCAGCAGTGAACCACCTCGGAGAAGACAAGGCAGTTCCAAAGAAGATACTAGGGATAATGAAGGTCAAACATTTGACAAGAGAGCAAGTTGCCAGTCATCTGCAGGTAATATTAAATACAGGATGCAACTGA
Protein Sequence
  • >LOC_Os10g32600.1
    MASSGDTNTVMKYVANGAFDFLLKPVRIEELSNIWQHIFRKQMQDHKNNNMVGNLEKPGHPPSILAMARATPATTRSTATEASLAPLENEVRDDMVNYNGEITDIRDLGKSRLTWTTQLHRQFIAAVNHLGEDKAVPKKILGIMKVKHLTREQVASHLQVILNTGCN*