Hd3a

Gene Details

MSU gene ID: LOC_Os06g06320
RAPdb gene ID: Os06g0157700
Gene Symbol: Hd3a
Genome: MSU7 , IRGSP-1.0
Species: Oryza sativa

Functional Descriptions

Hd3a, a rice ortholog of the Arabidopsis FT gene, promotes transition to flowering downstream of Hd1 under short-day conditions.
NB acts by downregulating Heading date 3a (Hd3a) expression.
The RNA levels of Heading date 3a (Hd3a), encoding a floral activator, are highly correlated with flowering time, and there is a high degree of polymorphism in the Heading date 1 (Hd1) protein, which is a major regulator of Hd3a expression.
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.
s73 mutant plants show a number of alterations in the characteristic diurnal expression patterns of master genes involved in photoperiodic control of flowering, resulting in up-regulation of the floral integrator Heading date3a (Hd3a).
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).
Genetic dissection of a genomic region for a quantitative trait locus, Hd3, into two loci, Hd3a and Hd3b, controlling heading date in rice.
Our results suggest that OsCO3 primarily controls flowering time under SD conditions by negatively regulating Hd3a and FTL expression, independent of the SD-promotion pathway.
RICE FLOWERING LOCUS T 1 (RFT1/FT-L3) is the closest homologue of Heading date 3a (Hd3a), which is thought to encode a mobile flowering signal and promote floral transition under short-day (SD) conditions.
These results indicate that Hd3a and RFT1 act as floral activators under SD conditions, and that RFT1 expression is partly regulated by chromatin modification.
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.
This suggests that the divergent functions of paralogs RFT1 and Hd3a, and of MADS50 and MADS51, are in part due to differential H3K36me2/3 deposition, which also correlates with higher expression levels of MADS50 and RFT1 in flowering promotion in rice.
By regulating Ehd1, RFT1, and Hd3a, Ghd8 delayed flowering under long-day conditions, but promoted flowering under short-day conditions.
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.
Because phytochrome B mutants do not respond to NB and their flowering time is not affected even under NB conditions, phyB is required for the suppression of Hd3a expression.
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.
A pair of floral regulators sets critical day length for Hd3a florigen expression in rice.
The expression patterns of Hd1 and Hd3a were also analyzed in different photoperiod and temperature conditions, revealing that Hd1 mRNA levels displayed similar expression patterns for different photoperiod and temperature treatments, with high expression levels at night and reduced levels in the daytime.
Hd3a mRNA was present at a very low level under low temperature conditions regardless of the day-length.
This result suggests that suppression of Hd3a expression is a principle cause of late heading under low temperature and long-day conditions.
We show that the protein encoded by Hd3a, a rice ortholog of FT, moves from the leaf to the shoot apical meristem and induces flowering in rice.
Here, we show that, unlike the Arabidopsis florigen gene FT, the rice florigen gene Hd3a (Heading date 3a) is toggled by only a 30-min day-length reduction.
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.
Suppression of the floral activator Hd3a is the principal cause of the night break effect in rice.
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.
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.
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.
These results suggested that OsDof12 might regulate flowering by controlling the expression of Hd3a and OsMADS14.
Furthermore, the expression of two regulators of flowering, Hd3a and OsMADS1, was also affected in the nl1 mutant.
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.
Phytochrome B regulates Heading date 1 (Hd1)-mediated expression of rice florigen Hd3a and critical day length in rice.
Expression analyses of flowering marker genes show that Rbs1 overexpression represses the expression of Hd3a under SD and LD conditions.
These results suggest that GF14c acts as a negative regulator of flowering by interacting with Hd3a.
The 14-3-3 protein GF14c acts as a negative regulator of flowering in rice by interacting with the florigen Hd3a.
A single NB strongly suppressed the mRNA of Hd3a, a homolog of Arabidopsis thaliana FLOWERING LOCUS T (FT), whereas the mRNAs of OsGI and Hd1 were not affected.
The phyB mutation abolished the NB effect on flowering and Hd3a mRNA, indicating that the NB effect was mediated by phytochrome B.
Because expression of the other FT-like genes was very low and not appreciably affected by NB, our results strongly suggest that the suppression of Hd3a mRNA is the principal cause of the NB effect on flowering in rice.
In rice, OsGI, Hd1 and Hd3a were identified as orthologs of GI, CO and FT, respectively, and are also important regulators of flowering.
Heading date 3a (Hd3a) has been detected as a heading-date-related quantitative trait locus in a cross between rice cultivars Nipponbare and Kasalath.
Many other features of the photoperiod genes revealed domestication signatures, which included high linkage disequilibrium (LD) within genes, the occurrence of frequent and recurrent non-functional Hd1 mutants in cultivated rice, crossovers between subtropical and tropical alleles of Hd1, and significant LD between Hd1 and Hd3a in japonica and indica.
Spin1 overexpression causes late flowering independently of daylength; expression analyses of flowering marker genes in these lines suggested that SPIN1 represses flowering by downregulating the flowering promoter gene Heading date3a (Hd3a) via Hd1-dependent mechanisms in short days and by targeting Hd1-independent factors in long days.
Here we show that the rice FT homologue Hd3a interacts with 14-3-3 proteins in the apical cells of shoots, yielding a complex that translocates to the nucleus and binds to the Oryza sativa (Os)FD1 transcription factor, a rice homologue of Arabidopsis thaliana FD.
Hd3a Protein Is a Mobile Flowering Signal in Rice.
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.
OsMADS51 is a short-day flowering promoter that functions upstream of Ehd1, OsMADS14, and Hd3a.
Our results suggest that quantitative effect of light on flowering in rice NB is mediated by the regulation of Hd3a transcription by phyB.
Phytochrome dependent quantitative control of Hd3a transcription is the basis of the night break effect in rice flowering.
Furthermore, the precocious flowering phenotype caused by the overexpression of Hd3a, a rice florigen gene, was weakened in pap2-1 mutants.
Ehd1 and Hd3a can also be down-regulated by the photoperiodic flowering genes Ghd7 and Hd1 (a rice ortholog of CONSTANS).
This indicates that LHD1 may delay flowering by repressing the expression of Ehd1, Hd3a and RFT1 under long-day conditions.
Although RFT1 RNAi plants flowered normally, double RFT1-Hd3a RNAi plants did not flower up to 300 days after sowing (DAS), indicating that Hd3a and RFT1 are essential for flowering in rice.
RFT1 expression was very low in wild-type plants, but there was a marked increase in RFT1 expression by 70 DAS in Hd3a RNAi plants, which flowered 90 DAS.
Hd3a and RFT1 are essential for flowering in rice.
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.
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.
Finally, we show that Hd3a promotes branching independently from strigolactone and FC1, a transcription factor that inhibits branching in rice.
Hd3a protein produced in the phloem reached the axillary meristem in the lateral bud, and its transport was required for promotion of branching.
Hd3a promotes lateral branching in rice.
We show here that Hd3a protein accumulated in axillary meristems to promote branching and that FAC formation was required.
Analysis of transgenic plants revealed that Hd3a promotes branching through lateral bud outgrowth.
Moreover, mutant Hd3a proteins defective in FAC formation but competent in transport failed to promote branching.
Together, these results suggest that Hd3a functions as a mobile signal for branching in rice.
Here, we confirm that Hd3a coexists, in the same regions of the rice shoot apex, with the other components of the florigen activation complex and its transcriptional targets.
The 14-3-3 proteins mediate the interaction of Hd3a with the transcription factor OsFD1 to form a ternary structure called the florigen activation complex on the promoter of OsMADS15, a rice APETALA1 ortholog.
Thus, the downregulation of Hd3a expression and the interaction between Cry1Ab/c and Hd3a interfere with Hd3a protein expression and might cooperatively delay HH1 flowering time.
We quantified the following: the expression of five major flowering genes in HH1, T1C-19, and MH63; florigen Hd3a protein expression levels in HH1 and MH63; interactions between Cry1Ab/c and the five main flowering proteins; and the effects of E3s ubiquitin ligase-mediated Cry1Ab/c expression on florigen Hd3a.
Foreign Cry1Ab/c Delays Flowering in Insect-Resistant Transgenic Rice via Interaction With Hd3a Florigen.

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