Hd1, Ghd7, and DTH8 synergistically determine the rice heading date and yield-related agronomic traits

Heading date determines the seasonal and regional adaptation of rice (Oryza sativa L.) varieties and is mainly controlled by photoperiod sensitivity (PS). The core heading date genes Hd1, Ghd7, DTH8, and PRR37 act synergistically in regulating the PS. In this study, we systematically analyze the heading date, PS, and agronomic traits of eight homozygous lines with various combinations of Hd1, Ghd7, and DTH8 alleles in the prr37 background under long-day (LD) and short-day (SD) conditions, respectively. We find that Hd1 alone promotes heading, regardless of the day length. However, under LDs, Hd1 suppresses flowering, in coordination with functional Ghd7 or with Ghd7 and DTH8. These loci cooperate to negatively regulate the Ehd1-Hd3a/RFT1 pathway and delay heading. Under SDs, Hd1 competes with various heading suppressors to promote heading. Therefore, the dual function of Hd1 is vital for PS. The lines carrying Hd1 alone show reduced plant height with fewer primary and secondary branches in panicles. Lines carrying Ghd7 and DTH8 (with hd1) show delayed heading and improve agronomic traits. Overall, our results reveal the regulation of rice PS flowering by the core heading date genes and their effects on agronomic traits, providing valuable information for the selection of rice varieties for adaptation to different light and temperature conditions.     

Ef7 encodes an ELF3-like protein and promotes rice flowering by negatively regulating the floral repressor gene Ghd7 under both short- and long-day conditions

Much progress has been made in our understanding of photoperiodic flowering of rice and the mechanisms underlying short-day (SD) promotion and long-day (LD) repression of floral induction. In this study, we identified and characterized the Ef7 gene, one of the rice orthologs of Arabidopsis EARLY FLOWERING 3 (ELF3). The ef7 mutant HS276, which was induced by γ-irradiation of the japonica rice cultivar 'Gimbozu', flowers late under both SD and LD conditions. Expression analyses of flowering time-related genes demonstrated that Ef7 negatively regulates the expression of Ghd7, which is a repressor of the photoperiodic control of rice flowering, and consequently up-regulates the expression of the downstream Ehd1 and FT-like genes under both SD and LD conditions. Genetic analyses with a non-functional Ghd7 allele provided further evidence that the delayed flowering of ef7 is mediated through the Ghd7 pathway. The analysis of light-induced expression of Ghd7 revealed that the ef7 mutant was more sensitive to red light than the wild-type plant, but the gate of Ghd7 expression was unchanged. Thus, our results show that Ef7 functions as a floral promoter by repressing Ghd7 expression under both SD and LD conditions.     

Diversified mechanisms for regulating flowering time in a short-day plant rice

Flowering in rice is influenced by not only endogenous factors that comprise an autonomous pathway, but also environmental effects, such as photoperiod, water availability, and temperature just before floral initiation. Recent molecular genetics studies have elucidated the functional roles of genes involved in the photoperiod pathway, e.g., photoreceptors, circadian clock components, and short-day (SD) promotion factors. Although these molecular players are well conserved between rice andArabidopsis, their actual genetic functions are distinct. This is exemplified byHd1 (aCO counterpart) and phytochromes, in particular, ricePHYA. Hd1 has a dual role in regulating flowering time and the expression ofHd3a (anFT counterpart) repression under long-day (LD) conditions while promotion under SDs. Models have been proposed to explain these photoperiod-dependent antagonistic activities. Some regulatory factors are present in only one of the model systems, e.g.,FLC inArabidopsis orEhd1 in rice. Furthermore, epistatic relationships vary among such flowering regulators asHd3a (FT), OsMADS50 (SOCT), andOsMADS14 (AP1). Further experiments to probe these differences will be essential to enlarging our understanding of the diversified flowering regulation mechanisms in rice.     

Comparison of rice flowering-time genes under paddy conditions

Heading date is one of most important agronomic traits in rice. Flowering regulatory mechanisms have been elucidated in many cultivars through various approaches. Although study about flowering has been extensively examined in rice, but contributions of floral regulators had been poorly understood in a common genetic background for rice grown under paddy conditions. Thus, we compared the expression of 10 flowering-time genes — OsMADS50, OsMADS51, OsVIL2, OsPhyA, OsPhyB, OsPhyC, Ghd7, Hd1, OsGI, and OsTrx1 — in the same genetic background for ‘Dongjin’ rice (Oryza sativa) grown under paddy conditions when days were longer than 13.5 h. Whereas the wild type (WT) rice flowered 105 days after sowing, the latest mutant to do so was ostrx1, flowering 53 d later. This indicated that the gene is the strongest inducer among all of those examined. Mutations in OsMADS50 delayed flowering by 45 d when compared with the WT, suggesting that this MADS gene is another strong positive element. The third positive element was OsVIL2; mutations in the gene caused plants to flower 27 d late. In contrast, the double phytochrome mutant osphyA osphyB flowered 44 d earlier than the WT. The single mutant osphyB and the double mutant osphyB osphyC did the same, although not as early as the osphyA osphyB double mutant. These results demonstrated that phytochromes are major inhibitors under paddy conditions. Mutations in Ghd7 accelerated flowering by 34 d, indicating that the gene is also a major inhibitor. The hd1 mutants flowered 16 d earlier than the WT while a mutation in OsGI hastened flowering by 10 d, suggesting that both are weak flowering repressors. Of the two florigen genes (Hd3a being the other one), RFT1 played a major role under paddy conditions. Its expression was strongly promoted by Ehd1, which was negatively controlled by Ghd7. Here we show that phytochromes strongly inhibit flowering and OsTrx1 and OsMADS50 significantly induce flowering under paddy conditions through Ghd7-Ehd1-RFT1 pathway. Thus, we may be able to control heading date under paddy conditions through manipulating those genes, Ghd7, Ehd1 and RFT1.     

Flowering time genes Heading date 1 and Early heading date 1 together control panicle development in rice

Although flowering time is often associated with plant size, little is known about how flowering time genes affect plant architecture. We grew four rice lines having different flowering time genotypes (hd1 ehd1, hd1 Ehd1, Hd1 ehd1 and Hd1 Ehd1) under distinct photoperiod conditions. By using genotype-treatment combinations that resulted in similar flowering times, we were able to compare the effects of flowering time genes on traits related to plant architecture. 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. 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. 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. 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.     

Combinations of Hd2 and Hd4 genes determine rice adaptability to Heilongjiang Province,northern limit of China

Heading date is a key trait in rice domestication and adaption, and a number of quantitative trait loci (QTLs) have been identified. The rice (Oryza sativa L.) cultivars in the Heilongjiang Province, t...     

Se14, Encoding a JmjC Domain-Containing Protein,Plays Key Roles in Long-Day Suppression of Rice Flowering through the Demethylation of H3K4me3 of RFT1

Floral transition from the vegetative to the reproductive growth phase is a major change in the plant life cycle and a key factor in reproductive success. In rice (Oryza sativa L.), a facultative short-day plant, numerous flowering time and flower formation genes that control floral transition have been identified and their physiological effects and biochemical functions have been clarified. In the present study, we used a Se14-deficient mutant line (HS112) and other flowering mutant lines to investigate the photoperiodic response, chromosomal location and function in the photoperiod sensitivity of the Se14 gene. We also studied the interactive effects of this locus with other crucial flowering time genes. We found that Se14 is independent of the known photoperiod-sensitive genes, such as Hd1 and Ghd7, and is identical to Os03g0151300, which encodes a Jumonji C (JmjC) domain-containing protein. Expression analysis revealed that the expressions of RFT1, a floral initiator known as a “florigen-like gene”, and Ehd1 were up-regulated in HS112, whereas this up-regulation was not observed in the original variety of ‘Gimbozu’. ChIP assays of the methylation states of histone H3 at lysine 4 (H3K4) revealed that the trimethylated H3K4 in the promoter region of the RFT1 chromatin was significantly increased in HS112. We conclude that Se14 is a novel photoperiod-sensitivity gene that has a suppressive effect on floral transition (flowering time) under long day-length conditions through the modification of chromatin structure by H3K4me3 demethylation in the promoter region of RFT1.     

水稻开花光周期调控相关基因研究进展

水稻开花调控是一个极其复杂的生命过程,由自身遗传因素和外界环境共同决定。光周期途径是调控水稻开花的关键途径,在这个途径中成花素基因Hd3a和RTF1处于核心地位,其上游调控途径主要包括Hd1依赖途径、Ehd1依赖途径及不依赖于Hd1和Ehd1的途径。这3条途径在汇集了光信号的各种信息后,将信号在Hd3a和RTF1处整合,并通过成花素形式将信息传递给下游开花基因,调控水稻开花。本文从成花素、光信号感受基因和昼夜节律基因、成花素上游调控基因、互作蛋白和下游调控基因等几方面阐述水稻开花光周期调控相关基因的研究现状,为水稻开花调控的深入研究提供参考。