Natural Long-day Conditions Research Articles

Expression of AtNF-YB1 activates early flowering, showing potential in breeding hybrid rice.

The nuclear factor Y (NF-Y) has been shown to be involved in plant growth and development in response to various environmental signals. However, the integration of these mechanisms into breeding practices for new cultivars has not been extensively investigated. In this study, the Arabidopsis gene AtNF-YB1 was introduced into rice, including inbred Kasalath and the hybrids Jinfeng × Chenghui 727 and Jinfeng × Chuanhui 907. The obtained transgenic rice showed early flowering under both natural long day (NLD) and natural short day (NSD) conditions. For the inbred Kasalath, the transgenic lines clearly showed a shorter plant height and lower grain yield, with a decrease in spike length and grain number but more productive panicles. However, the hybrids with AtNF-YB1 had much smaller or even zero reduction in spike length and grain number and more productive panicles. Thus, maintained or even increased grain yields of the transgenic hybrids were recorded under the NLD conditions. Quantitative PCR analysis indicated that the rice flowering initiation pathways were early activated via the suppression of Ghd7 induction in the transgenic rice. RNA-Seq further demonstrated that three pathways related to plant photosynthesis were markedly upregulated in both Jinfeng B and the hybrid Jinfeng × Chuanhui 907 with AtNF-YB1 expression. Moreover, physiological experiments showed an upregulation of photosynthetic rates in the transgenic lines. Taken together, this study suggests that AtNF-YB1 expression in rice not only induces early flowering but also benefits photosynthesis, which might be used to develop hybrid varieties with early ripening.

Knockout of OsWOX13 moderately delays flowering in rice under natural long-day conditions.

Plants are sensitive to photoperiods and are also equipped with systems to adjust their flowering time in response to various changes in the environment and developmental hormones. In the present study, previously generated rice OsWOX13 overexpression and newly generated OsWOX13 knockout lines constructed via CRISPR/Cas9 technology flowered 10 days earlier and 4-6 days later than the wild type, respectively. Quantitative real-time polymerase chain reaction analyses revealed that OsWOX13 might be involved in drought escape responses through the b-ZIP TRANSCRIPTION FACTOR 23 signaling pathway during rice flowering via photoperiod signaling genes such as Grain number, plant height and heading date 7, Early heading date 1, RICE FLOWERING LOCUS T1, Heading date 3a, and MADS14. Future investigations of OsWOX13 may provide insight into how plants adjust their flowering under stress conditions and how OsWOX13 could be precisely controlled to achieve maximum productivity in rice breeding.

Mutations of Two Florigen Genes have Different Effects on Controlling Flowering Time in Rice Under Natural Long-Day Conditions

Mutations of Two Florigen Genes have Different Effects on Controlling Flowering Time in Rice Under Natural Long-Day Conditions

Influence of Bradyrhizobium japonicum on the growth parameters and formation of the assimilation apparatus in E-gene isogenic lines of soybean

The study investigated the impact of the interaction between soybean and rhizobia on the assimilation apparatus functioning and biomass accumulation in different soybean lines with varying photoperiod sensitivity. Nearly isogenic lines (NILs) of soybean were used, with genes E1, E2, and E3 in different allelic states: Clark (e1E2E3), L80-5879 (E1e2e3), L63-3117 (e1e2E3), and L71-920 (e1e2e3). The experimental group for each line was treated with Bradyrhizobium japonicum 634b. Plants were grown under natural long-day conditions (16 hours). Growth indicators of the studied lines, such as relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), and specific leaf area (SLA), were analyzed, as well as the content of chlorophylls A and B in the V3 and V5 developmental stages. The results demonstrate that the influence of rhizobia on the functioning of the assimilation apparatus and biomass accumulation depends on the soybean line genotype. In the study, RGR, which characterizes the biomass accumulation rate, has similar trends to those observed with NAR, characterizing the assimilation apparatus's functioning. However, each line showed its own tendencies. For instance, in the short-day variety Clark, under bacterial influence, the value of RGR and NAR decreased. Additionally, LAR and SLA values indicated a reduction in the total photosynthetic surface area and leaf dry matter. Bacterial inoculation did not significantly affect the content of photosynthetic pigments in Clark leaves. Another short-day line, L80-5879, showed no significant impact of bacterial inoculation on biomass accumulation. However, soybean interaction with Bradyrhizobium japonicum 634b led to a decrease in leaf surface area and dry matter content. Probably, bacterial inoculation supported assimilation processes by increasing auxiliary chlorophyll b in photosystem I. A general trend of significant RGR reduction in neutral-day soybean lines, L63-3117 and L71-920, was identified under bacterial influence. The interaction with rhizobia differently affected LAR and SLA values, indicating distinct adaptive mechanisms to the interactions. In conditions of almost zero plant biomass accumulation, Bradyrhizobium japonicum 634b caused a decrease in the total photosynthetic surface area and chlorophyll a and b content in the L63-3117 line. In L71-920, bacterial inoculation had no effect on the total photosynthetic surface area, while leaf dry matter and photosynthetic pigment content decreased. The obtained results demonstrate that interaction with rhizobia can influence the functioning of the assimilation apparatus in soybeans with varying photoperiod sensitivity that is determined by genotype. It is important in improving soybean productivity and its application in agricultural practices.

Low temperature-mediated repression and far-red light-mediated induction determine morning FLOWERING LOCUS T expression levels.

In order to flower in the appropriate season, plants monitor light and temperature changes and alter downstream pathways that regulate florigen genes such as Arabidopsis (Arabidopsis thaliana) FLOWERING LOCUS T (FT). In Arabidopsis, FT messenger RNA levels peak in the morning and evening under natural long-day conditions (LDs). However, the regulatory mechanisms governing morning FT induction remain poorly understood. The morning FT peak is absent in typical laboratory LDs characterized by high red:far-red light (R:FR) ratios and constant temperatures. Here, we demonstrate that ZEITLUPE (ZTL) interacts with the FT repressors TARGET OF EATs (TOEs), thereby repressing morning FT expression in natural environments. Under LDs with simulated sunlight (R:FR = 1.0) and daily temperature cycles, which are natural LD-mimicking environmental conditions, FT transcript levels in the ztl mutant were high specifically in the morning, a pattern that was mirrored in the toe1 toe2 double mutant. Low night-to-morning temperatures increased the inhibitory effect of ZTL on morning FT expression by increasing ZTL protein levels early in the morning. Far-red light counteracted ZTL activity by decreasing its abundance (possibly via phytochrome A (phyA)) while increasing GIGANTEA (GI) levels and negatively affecting the formation of the ZTL-GI complex in the morning. Therefore, the phyA-mediated high-irradiance response and GI play pivotal roles in morning FT induction. Our findings suggest that the delicate balance between low temperature-mediated ZTL activity and the far-red light-mediated functions of phyA and GI offers plants flexibility in fine-tuning their flowering time by controlling FT expression in the morning.

Influence of genotype and bacterization on growth, development, and soluble carbohydrate content in soybean E-genes isogenic lines

Photoperiod, which regulates the duration of vegetative and generative development, and the plant-microorganism interaction, which influences the metabolic status of plant organisms, are important factors in the regulating plant growth and development. The aim of the study was to determine the influence of Glycine max (L.) Merr. genotype and seed pre-bacterization with a virulent and active strain of Bradyrhizobium japonicum 634b on the plant growth and development, and on the soluble carbohydrate content in leaves of isogenic by E-genes lines under field conditions. Nearly isogenic lines (NILs) of soybean, in which the E1, E2, and E3 genes are located at different allelic loci, were used. Sterile seeds were pretreated with distilled water (control) and Bradyrhizobium japonicum 634b cell suspension (experiment). Plants were grown under natural long-day conditions (16 hours). The growth and development of the soybean were evaluated by phenological observations, morphometric indicators fixed at the V3 and V5 developmental stages, relative growth rate (RGR), and the content of soluble sugars ‒ mono- and oligosaccharides. The effect of the factors studied (genotype, bacterization, and their interaction) was calculated. The results of the experiment and the calculation of the effect of the factor showed that the isoline genotype has the greatest effect on seed germination, phenological development of the plant and duration of the VE-R1 phase, growth of the root system in the V3 and V5 phases, and the content of monosaccharides involved in forming the plant-microorganism interaction. The effect of bacterization is most evident in the RGR, shoot development, and the oligosaccharide content of the leaves of NILs in the V3 and V5 phases. Among the isolines studied, L 80-5879, which has the E1 gene (flowering repressor) in a dominant state, was characterized by minimal sensitivity to bacterization. It was found that bacterization and genotype interaction didn't influence the VE-R1 duration stage and the shoot and root length. The results obtained therefore prove that the E-series genes, which determine the photoperiodic sensitivity of soya beans, can also be indirectly involved in establishing plant-microorganism interactions.

Photoperiod and gravistimulation-associated Tiller Angle Control 1 modulates dynamic changes in rice plant architecture.

TAC1 is involved in photoperiodic and gravitropic responses to modulate rice dynamic plant architecture likely by affecting endogenous auxin distribution, which could explain TAC1 widespread distribution in indica rice. Plants experience a changing environment throughout their growth, which requires dynamic adjustments of plant architecture in response to these environmental cues. Our previous study demonstrated that Tiller Angle Control 1 (TAC1) modulates dynamic changes in plant architecture in rice; however, the underlying regulatory mechanisms remain largely unknown. In this study, we show that TAC1 regulates plant architecture in an expression dose-dependent manner, is highly expressed in stems, and exhibits dynamic expression in tiller bases during the growth period. Photoperiodic treatments revealed that TAC1 expression shows circadian rhythm and is more abundant during the dark period than during the light period and under short-day conditions than under long-day conditions. Therefore, it contributes to dynamic plant architecture under long-day conditions and loose plant architecture under short-day conditions. Gravity treatments showed that TAC1 is induced by gravistimulation and negatively regulates shoot gravitropism, likely by affecting auxin distribution. Notably, the tested indica rice containing TAC1 displayed dynamic plant architecture under natural long-day conditions, likely explaining the widespread distribution of TAC1 in indica rice. Our results provide new insights into TAC1-mediated regulatory mechanisms for dynamic changes in rice plant architecture.

The FLOWERING LOCUS T gene expression is controlled by high-irradiance response and external coincidence mechanism in long days in Arabidopsis.

In natural long days, the florigen gene FLOWERING LOCUS T (FT) shows a bimodal expression pattern with morning and dusk peaks in Arabidopsis. This pattern differs from the one observed in the laboratory, and little is known about underlying mechanisms. A red : far-red (R : FR) ratio difference between sunlight and fluorescent light causes this FT pattern mismatch. We showed that bimodal FT expression patterns were induced in a day longer than 14 h with sunlight R : FR (= c. 1) conditions. By circadian gating experiments, we found that cumulative exposure of R : FR-adjusted light (R : FR ratio was adjusted to 1 with FR supplement) spanning from the afternoon to the next morning required full induction of FT in the morning. Conversely, only 2 h of R : FR adjustment in the late afternoon was sufficient for FT induction at dusk. We identified that phytochrome A (phyA) is required for the morning FT expression in response to the R : FR adjustment on the previous day. As a part of this mechanism, we showed that PHYTOCHROME-INTERACTING FACTOR 7 contributes to FT regulation. Our results suggest that phyA-mediated high-irradiance response and the external coincidence mechanism contribute to morning FT induction under natural long-day conditions.

CRISPR/Cas9-engineered mutation to identify the roles of phytochromes in regulating photomorphogenesis and flowering time in soybean

Soybean (Glycine max) responds to ambient light variation by undergoing multiform morphological alterations, influencing its yield potential and stability in the field. Phytochromes (PHYs) are plant-specific red (R) and far-red (FR) light photoreceptors mediating photomorphogenesis and photoperiodic flowering. As an ancient tetraploid, soybean harbors four PHYA, two PHYB, and two PHYE paralogs. Except for GmPHYA2/E4 and GmPHYA3/E3, which have been identified as photoperiod-dependent flowering repressors, the functions of GmPHYs are still largely unclear. We generated a series of individual or combined mutations targeting the GmPHYA or GmPHYB genes using CRISPR/Cas9 technology. Phenotypic analysis revealed that GmPHYB1 mediates predominantly R-light induced photomorphogenesis, whereas GmPHYA2/E4 and GmPHYA3/E3, followed by GmPHYA1 and GmPHYB2, function redundantly and additively in mediating FR light responses in seedling stage. GmPHYA2/E4 and GmPHYA3/E3, with weak influence from GmPHYA1 and GmPHYA4, delay flowering time under natural long-day conditions. This study has demonstrated the diversified functions of GmPHYAs and GmPHYBs in regulating light response, and provides a core set of phytochrome mutant alleles for characterization of their functional mechanisms in regulating agronomic traits of soybean.

OsVQ1 links rice immunity and flowering via interaction with a mitogen-activated protein kinase OsMPK6.

Knocking out OsVQ1 in rice released OsMPK6 for activation and in turn promoted H2O2 accumulation, which repressed the expression of flowering-promoting genes, thus delaying rice flowering but enhancing disease resistance. The valine-glutamine (VQ) protein family, which contains the conserved motif FxxxVQxLTG ("x" represents any amino acid), plays a crucial role in plant growth and immunity along with mitogen-activated protein kinase (MAPK) cascades. However, only a few rice VQ proteins have been functionally characterized, and the roles of the MAPK-VQ module in rice biological processes are not fully understood. Here, we investigated the role of OsVQ1 in rice disease resistance and the control of flowering time. The OsVQ1-knock out (KO) mutants exhibited increased resistance to Xanthomonas oryzae pathovars, accumulated high levels of hydrogen peroxide (H2O2), and showed a late flowering phenotype under natural long-day conditions, while the OsVQ1-overexpressing plants showed phenotypes similar to that of the wild type. Further studies revealed that OsVQ1 physically interacted with and inhibited OsMPK6 activity. In addition, OsVQ1 expression was downregulated by the pathogen-induced OsMPKK10.2-OsMPK6-OsWRKY45 cascade, suggesting a feedback loop between OsVQ1 and OsMPK6. Moreover, the OsVQ1-KO/osmpk6 double-mutant exhibited increased susceptibility to X. oryzae infection and showed an early flowering phenotype, which may partially be attributed to the reduced accumulation of H2O2 and the consequent up-expression of flowering-promoting genes. These results suggested that the OsVQ1-OsMPK6 module was involved in rice immunity and flowering.

OsPRR37 Alternatively Promotes Heading Date Through Suppressing the Expression of Ghd7 in the Japonica Variety Zhonghua 11 under Natural Long-Day Conditions

Heading date is an important agronomic trait of rice (Oryza sativa L.) and is regulated by numerous genes, some of which exhibit functional divergence in a genetic background-dependent manner. Here, we identified a late heading date 7 (lhd7) mutant that flowered later than wild-type Zhonghua 11 (ZH11) under natural long-day (NLD) conditions. Map-based cloning facilitated by the MutMap strategy revealed that LHD7 was on the same locus as OsPRR37 but exhibited a novel function as a promoter of heading date. A single-nucleotide mutation of G-to-A in the coding region caused a substitution of aspartic acid for glycine at site 159 within the pseudo-receiver (PR) domain of OsPRR37. Transcriptional analysis revealed that OsPRR37 suppressed Ghd7 expression in both ZH11 background under NLD conditions and the Zhenshan 97 background under natural short-day conditions. Consistently, the expression of Ehd1, Hd3a and RFT1 was enhanced by OsPRR37 in the ZH11 background. Genetic analysis indicated that the promotion of heading date and reduction in grain yield by OsPRR37 were partially dependent on Ghd7. Further investigation showed that the alternative function of OsPRR37 required an intact Ghd7-related regulatory pathway involving not only its upstream regulators OsGI and PhyB but also its interacting partner Hd1. Our study revealed the distinct role of OsPRR37 in the ZH11 background, which provides a more comprehensive understanding of OsPRR37 function and enriches the theoretical bases for improvement of rice heading date in the future.

DHD4, a CONSTANS-like family transcription factor, delays heading date by affecting the formation of the FAC complex in rice

Heading date (or flowering time) is one of the most important agronomic traits in rice, influencing its regional adaptability and crop yield. Many major-effect genes for rice heading date have been identified, but in practice they are difficult to be used for rice molecular breeding because of their dramatic effects on heading date. Genes with minor effects on heading date, which are more desirable for fine-tuning flowering time without significant yield penalty, were seldom reported. In this study, we identified a new minor-effect heading date repressor, Delayed Heading Date 4 (DHD4). The dhd4 mutant shows a slightly earlier flowering phenotype without a notable yield penalty compared with wild-type plants under natural long-day conditions. DHD4 encodes a CONSTANS-like transcription factor localized in the nucleus. Molecular, biochemical, and genetic assays show that DHD4 can compete with 14-3-3 to interact with OsFD1, thus affecting the formation of the Hd3a-14-3-3-OsFD1 tri-protein FAC complex, resulting in reduced expression of OsMADS14 and OsMADS15, and ultimately delaying flowering. Taken together, these results shed new light on the regulation of flowering time in rice and provide a promising target for fine-tuning flowering time to improve the regional adaptability of rice.

Genetic Interactions Among Ghd7, Ghd8, OsPRR37 and Hd1 Contribute to Large Variation in Heading Date in Rice

BackgroundHeading date is crucial for rice reproduction and geographic expansion. Many heading date genes are sensitive to photoperiod and jointly regulate flowering time in rice. However, it is not clear how these genes coordinate rice heading.ResultsHere, we performed a genetic interaction analysis among four major rice heading date genes Ghd7, Ghd8, OsPRR37/Ghd7.1 (hereafter PRR37) and Hd1 in the near-isogenic background under both natural long-day (NLD) and natural short-day (NSD) conditions. The 4-gene segregating population exhibited a large heading date variation with more than 95 days under NLD and 42 days under NSD conditions. Tetragenic, trigenic and digenic interactions among these four genes were observed under both conditions but more significant under NLD conditions. In the functional Hd1 backgrounds, the strongest digenic interaction was Ghd7 by Ghd8 under NLD but was Ghd7 by PRR37 under NSD conditions. Interestingly, PRR37 acted as a flowering suppressor under NLD conditions, while it functioned alternatively as an activator or a suppressor under NSD conditions depending on the status of the other three genes. Based on the performances of 16 homozygous four-gene combinations, a positive correlation between heading date and spikelets per panicle (SPP) was found under NSD conditions, but changed to a negative correlation when heading date was over 90 days under NLD conditions.ConclusionsThese results demonstrate the importance of genetic interactions in the rice flowering regulatory network and will help breeders to select favorable combinations to maximize rice yield potential for different ecological areas.

Early heading 7 interacts with DTH8, and regulates flowering time in rice.

EH7/Ghd7 interacts with DTH8, and regulates heading date by controlling the expression of Ehd1 in rice. Heading date, or flowering time, an important agronomic trait, influences regional adaptability and yield of crops. Many genes related to heading date in rice have been identified, and a preliminary regulatory network has been established, but the relationships between proteins involved are poorly understood. We identified a flowering suppressor EH7 (Early heading 7) that represses flowering under long-day (LD) conditions. The eh7 allele caused earlier heading, shorter plant height and less grain per main panicle than did the wild type (WT), but the tiller number and 1000-grain weight were not significantly affected under natural long-day conditions. Biochemical assays showed that EH7 interacts with DTH8. Quantitative PCR showed that EH7 inhibited heading date by downregulating the expression of Ehd1, Hd3a and RFT1. We propose that EH7 interacts with DTH8 to control flowering time by regulating the expression of Ehd1, Hd3a and RFT1.

Importance of the Interaction between Heading Date Genes Hd1 and Ghd7 for Controlling Yield Traits in Rice.

Appropriate flowering time is crucial for successful grain production, which relies on not only the action of individual heading date genes, but also the gene-by-gene interactions. In this study, influences of interaction between Hd1 and Ghd7 on flowering time and yield traits were analyzed using near isogenic lines derived from a cross between indica rice cultivars ZS97 and MY46. In the non-functional ghd7ZS97 background, the functional Hd1ZS97 allele promoted flowering under both the natural short-day (NSD) conditions and natural long-day (NLD) conditions. In the functional Ghd7MY46 background, Hd1ZS97 remained to promote flowering under NSD conditions, but repressed flowering under NLD conditions. For Ghd7, the functional Ghd7MY46 allele repressed flowering under both conditions, which was enhanced in the functional Hd1ZS97 background under NLD conditions. With delayed flowering, spikelet number and grain weight increased under both conditions, but spikelet fertility and panicle number fluctuated. Rice lines carrying non-functional hd1MY46 and functional Ghd7MY46 alleles had the highest grain yield under both conditions. These results indicate that longer growth duration for a larger use of available temperature and light does not always result in higher grain production. An optimum heading date gene combination needs to be carefully selected for maximizing grain yield in rice.

Gene diagnosis and targeted breeding for blast-resistant Kongyu 131 without changing regional adaptability

The fungus Magnaporthe oryzae threatens the rice production of Kongyu 131 (KY131), a leading japonica variety in Northeast China. In this study, two rice lines, KP1 and KP2-Hd1, were obtained by introgressing the blast resistance genes Pi1 and Pi2 into KY131, respectively. However, both lines headed later than KY131. RICE60K SNP array analysis showed that Hd1 closely linked to Pi2 was introgressed into KP2-Hd1, and the linkage drag of Hd1 was broken by recombination. On the other hand, no known flowering genes were introgressed into KP1. Gene diagnosis by resequencing six flowering genes showed that KP1 carried functional Hd16 and Ghd8 alleles. Due to its suppression role in heading under long-day conditions, Ghd8 was chosen as the target for gene editing to disrupt its function. Four sgRNAs targeting different sites within Ghd8 were utilized to induce large-deletion mutations, which were easy to detect via agarose gel electrophoresis. All the ghd8-mutated KP1 lines were resistant to rice blast disease and headed earlier than the control KP1, even than KY131, under natural long-day conditions, which ensures its growth in Northeast China. This study confirmed that a combination of gene diagnosis and targeted gene editing is a highly efficient way to quickly eliminate undesired traits in a breeding line.

Molecular basis of flowering under natural long-day conditions in Arabidopsis.

Plants sense light and temperature changes to regulate flowering time. Here we show that expression of the Arabidopsis florigen gene, FLOWERING LOCUS T (FT), peaks in the morning during spring, a different pattern than we observe in the lab. Providing our lab growth conditions with a red/far-red light ratio similar to open field conditions and daily temperature oscillation is sufficient to mimic the FT expression and flowering time in natural long days. Under the adjusted growth conditions, key light signaling components, such as phytochrome A (phyA) and EARLY FLOWERING 3 (ELF3), play important roles in morning FT expression. These conditions stabilize CONSTANS (CO) protein, a major FT activator, in the morning, which is likely a critical mechanism for photoperiodic flowering in nature. Refining the parameters of our standard growth conditions to more precisely mimic plant responses in nature can provide a powerful method for improving our understanding of seasonal response.

The Oryza sativa Regulator HDR1 Associates with the Kinase OsK4 to Control Photoperiodic Flowering.

Rice is a facultative short-day plant (SDP), and the regulatory pathways for flowering time are conserved, but functionally modified, in Arabidopsis and rice. Heading date 1 (Hd1), an ortholog of Arabidopsis CONSTANS (CO), is a key regulator that suppresses flowering under long-day conditions (LDs), but promotes flowering under short-day conditions (SDs) by influencing the expression of the florigen gene Heading date 3a (Hd3a). Another key regulator, Early heading date 1 (Ehd1), is an evolutionarily unique gene with no orthologs in Arabidopsis, which acts as a flowering activator under both SD and LD by promoting the rice florigen genes Hd3a and RICE FLOWERING LOCUST 1 (RFT1). Here, we report the isolation and characterization of the flowering regulator Heading Date Repressor1 (HDR1) in rice. The hdr1 mutant exhibits an early flowering phenotype under natural LD in a paddy field in Beijing, China (39°54'N, 116°23'E), as well as under LD but not SD in a growth chamber, indicating that HDR1 may functionally regulate flowering time via the photoperiod-dependent pathway. HDR1 encodes a nuclear protein that is most active in leaves and floral organs and exhibits a typical diurnal expression pattern. We determined that HDR1 is a novel suppressor of flowering that upregulates Hd1 and downregulates Ehd1, leading to the downregulation of Hd3a and RFT1 under LDs. We have further identified an HDR1-interacting kinase, OsK4, another suppressor of rice flowering under LDs. OsK4 acts similarly to HDR1, suppressing flowering by upregulating Hd1 and downregulating Ehd1 under LDs, and OsK4 can phosphorylate HD1 with HDR1 presents. These results collectively reveal the transcriptional regulators of Hd1 for the day-length-dependent control of flowering time in rice.

Rice FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (OsFKF1) promotes flowering independent of photoperiod.

In the facultative long-day (LD) plant Arabidopsis thaliana, FLAVIN-BINDING, KELCH REPEAT, F-BOX 1 (FKF1) is activated by blue light and promotes flowering through the transcriptional and post-translational regulation of CONSTANS under inductive LD conditions. By contrast, the facultative short day (SD) plant rice (Oryza sativa) flowers early under inductive SD and late under non-inductive LD conditions; the regulatory function of OsFKF1 remains elusive. Here we show that osfkf1 mutants flower late under SD, LD and natural LD conditions. Transcriptional analysis revealed that OsFKF1 up-regulates the expression of the floral activator Ehd2 and down-regulates the expression of the floral repressor Ghd7; these regulators up- and down-regulate Ehd1 expression, respectively. Moreover, OsFKF1 can up-regulate Ehd1 expression under blue light treatment, without affecting the expression of Ehd2 and Ghd7. In contrast to the LD-specific floral activator Arabidopsis FKF1, OsFKF1 likely acts as an autonomous floral activator because it promotes flowering independent of photoperiod, probably via its distinct roles in controlling the expression of rice-specific genes including Ehd2, Ghd7 and Ehd1. Like Arabidopsis FKF1, which interacts with GI and CDF1, OsFKF1 also interacts with OsGI and OsCDF1 (also termed OsDOF12). Thus, we have identified similar and distinct roles of FKF1 in Arabidopsis and rice.

EF8 is involved in photoperiodic flowering pathway and chlorophyll biogenesis in rice.

A DTH8/Ghd8 allele suppresses flowering by altering the expression patterns of the 'florigen' genes, but also negatively regulates chlorophyll biogenesis. Flowering time is a critical agronomic trait determining the growing season, regional adaptation and yield potential in rice (Oryza sativa L.). We characterized a mutant named early flowering 8 (ef8) selected from an ethyl methanesulfonate (EMS)-treated population of indica cultivar 93-11. It showed earlier flowering, less grains per main panicle and slightly darker green leaves than the wild-type 93-11 under natural long-day conditions, but was not significantly different from 93-11 under natural short-day conditions. We isolated the Early Flowering 8 (EF8) gene by map-based cloning. EF8 encodes a putative HAP3 subunit of the CCAAT-box-binding transcription factor, which is localized to the nucleus. EF8 was expressed in various tissues, especially in leaves, with a rhythmic expression pattern. Our data showed that EF8 delayed flowering time under long-day conditions by altering the rhythmic expression patterns of 'florigen' genes Hd3a and RFT1. We also found that EF8 negatively regulates the expression of chlorophyll biosynthetic genes to reduce the chlorophyll content. Our data indicate that EF8 plays an important role in rice photoperiodic flowering pathway as well as yield potential and chlorophyll biogenesis and will be an important target for rice breeding programs.