FT Gene Research Articles

Endogenous phytohormones and the expression of flowering genes synergistically induce flowering in loquat

Flowering is an important process for the reproduction of higher plants. Up to this point, the studies on flowering have mostly focused on the model plant Arabidopsis thaliana, and the flowering mechanism of fruit trees remains mostly unknown. The diversity of the flowering time of loquat (Eriobotrya japonica Lindl.) makes it an ideal material to study the regulation of flowering. In this study, we first observed the inflorescence bud differentiation in two varieties of loquat that had different blooming times (cv. Dawuxing (E. japonica), that blooms in the fall and cv. Chunhua (E. japonica×Eriobotrya bengalensis Hook. f.) that blooms in the spring) and found that the starting time of inflorescence bud differentiation and the speed of inflorescence development were responsible for the difference in blooming times. The determination of endogenous phytohormones by high performance liquid chromatography (HPLC) indicated that abscisic acid (ABA), zeatin (ZT), and gibberellin (GA3) promoted flowering in loquat, while indole-3-acetic acid (IAA) was mainly involved in inflorescence bud differentiation in Chunhua. A transcription level analysis illustrated that multiple flowering-related genes could respond to different signals, integrate to the TFL1, AP1 and FT genes, and then synergistically regulate flowering in loquat. Thus, this study provides a new insight into flowering regulation mechanisms in loquat.

The HD-ZIP IV transcription factor GL2-LIKE regulates male flowering time and fertility in cucumber.

Cucumber is dioecious by nature, having both male and female flowers, and is a model system for unisexual flower development. Knowledge related to male flowering is limited, but it is reported to be regulated by transcription factors and hormone signals. Here, we report functional characterization of the cucumber (Cucumis sativus) GL2-LIKE gene, which encodes a homeodomain leucine zipper (HD-ZIP) IV transcription factor that plays an important role in regulating male flower development. Spatial-temporal expression analyses revealed high-level expression of CsGL2-LIKE in the male flower buds and anthers. CsGL2-LIKE is closely related to AtGL2, which is known to play a key role in trichome development. However, ectopic expression of CsGL2-LIKE in Arabidopsis gl2-8 mutant was unable to rescue the gl2-8 phenotype. Interestingly, the silencing of CsGL2-LIKE delayed male flowering by inhibiting the expression of the florigen gene FT and reduced pollen vigor and seed viability. Protein-protein interaction assays showed that CsGL2-LIKE interacts with the jasmonate ZIM domain protein CsJAZ1 to form a HD-ZIP IV-CsJAZ1 complex. Collectively, our study indicates that CsGL2-LIKE regulates male flowering in cucumber, and reveals a novel function of a HD-ZIP IV transcription factor in regulating male flower development of cucumber.

Molecular cloning and functional characterization of CmFT (FLOWERING LOCUS T) from Cucumis melo L.

CmFT homologous gene in muskmelon was obtained by homologous cloning, introducing CmFT gene by Agrobacterium mediated transformation. The results of subcellular localization showed that CmFT protein was expressed in cytoplasm and nucleus. qRTPCR results showed that the expression levels of AtLFY, AtFT, AtCO, AtFLC, AtSOC1 and AtAP1 were upregulated in the 35S::MeFT Arabidopsis line. The CmFT gene was introduced into wild-type Arabidopsis by Agrobacterium-mediated transformation, and the growth status of T2 transgenic Arabidopsis thaliana and wild-type A. thaliana was observed. The results showed that wild-type Arabidopsis began to bolt on the 25th day after sowing, we can initially confirm that the FT gene of melon can promote the early flowering of melon in the growth and development of melon.

An Insertion Mutation in Bra032169 Encoding a Histone Methyltransferase Is Responsible for Early Bolting in Chinese Cabbage (Brassica rapa L. ssp. pekinensis).

Bolting is an important agronomic character of the Chinese cabbage, but premature bolting can greatly reduce its commercial value, yield, and quality. Here, early-bolting mutant 1 (ebm1) was obtained from a Chinese cabbage doubled haploid (DH) line “FT,” by using an isolated microspore culture and ethyl methanesulfonate (EMS) mutagenesis. The ebm1 was found to bolt extremely earlier than the wild type “FT.” Genetic analysis indicated that the phenotype of the ebm1 was controlled by a single recessive nuclear gene. Using a mapping population of 1,502 recessive homozygous F2 individuals with the ebm1 phenotype, the ebm1 gene was mapped to between the markers SSRhl-53 and SSRhl-61 on chromosome A04 by using SSR markers, and its physical distance was 73.4 kb. Seven genes were predicted in the target region and then cloned and sequenced; the only difference in the sequences of the ebm1 and “FT” genes was with Bra032169. Unlike that in “FT,” the Bra032169 in ebm1 had a novel 53 bp insertion that caused the termination of amino acid coding. The mutation was not consistent with EMS mutagenesis, and thus, may have been caused by spontaneous mutations during the microspore culture. Based on the gene annotation information, Bra032169 was found to encode the histone methyltransferase CURLY LEAF (CLF) in Arabidopsis thaliana. CLF regulates the expression of flowering-related genes. Further genotyping revealed that the early-bolting phenotype was fully co-segregated with the insertion mutation, suggesting that Bra032169 was the most likely candidate gene for ebm1. No significant differences were noted in the Bra032169 expression levels between the ebm1 and “FT.” However, the expression levels of the flowering-related genes FLC, FT, AG, and SEP3 were significantly higher in the ebm1 than in the “FT.” Thus, the mutation of Bra032169 is responsible for the early-bolting trait in Chinese cabbage. These results provide foundation information to help understand the molecular mechanisms of bolting in the Chinese cabbage.

Increased BnaMFT-transcript level is associated with secondary dormancy in oilseed rape (Brassica napus L.)

Brassica napus cultivars have little or no primary dormancy; however, they are prone to secondary dormancy induction. Secondary dormant seeds can produce volunteer plants, which can result in genetic contamination, reduced quality and biosafety issues. However, information regarding the molecular mechanism underlying secondary dormancy is limited. The MOTHER OF FT AND TFL1 (MFT) gene, which is evolutionarily conserved in the plant kingdom, acts in a complex gene network in the seed dormancy or germination processes. In this study, we identified four B. napus genes that share high homology with AtMFT, named as BnaMFT. Analyses of cis-acting elements showed that BnaMFT promoters contain multiple seed-specific regulatory elements, and various stress- and hormone-responsive elements. Further experiments validated that BnaMFTs were specifically expressed during seed maturation and in the dry seed, with peaks at 35–42 days after pollination. BnaMFTs were not sufficient for primary dormancy; however, they were significantly enhanced by secondary dormancy induction with PEG6000 treatment. Moreover, BnaMFT transcripts were elevated by treatment with abscisic acid (ABA), which is known to be accumulated during secondary dormancy. These results collectively suggest that increased BnaMFT transcription levels are associated with secondary dormancy induction in an ABA-dependent manner in B. napus.

QTL analysis of shoot elongation before winter in relation to vernalization requirement in the doubled haploid population L16\u2009\xd7\u2009Express617 (Brassica napus L.)

In winter oilseed rape shoot elongation before winter is considered as a critical component of the complex trait winter hardiness. Genotypes with an enhanced shoot length before winter are very much prone to frost damage. However, it is not known to which extent shoot elongation before winter is related to vernalization requirement. Shoot length measured 3 months after sowing of winter oilseed rape in spring has been shown to be a good quantitative estimator for vernalization requirement. The main objective of this study was to analyze inheritance of shoot elongation before winter and in spring-sown field experiments using a doubled haploid population derived from the cross between two inbred lines. A SNP based molecular marker map was used to map QTL for shoot length and flowering time. Significant genotypic effects were detected for shoot length before winter and in the spring-sown environment, but there was no correlation between both traits. Six QTL for shoot length before winter contributed 49.2% to the phenotypic variance. For shoot length in the spring-sown environment three QTL were detected that explained 68% of the phenotypic variance. Flowering time genes CONSTANS (BnaC09g41980D), FLC (BnaC09g42060D) and FT (BnaA02g12130D) were identified within C09 and A02 QTL confidence intervals. No collocation of QTL for shoot length before winter and for shoot length in the spring-sown environment was found. Results show that selection for reduced shoot length before winter would be effective and that this trait is inherited largely independent of vernalization requirement.

Determinate growth habit of grain legumes: role in domestication and selection, genetic control

This review is devoted to the analysis of molecular genetic mechanisms of controlling the type of growth habit of grain legumes (pea, soybean, common bean, vigna); it provides information about known homologous genes TFL1, LFY, AP1, FUL, FT, and FD. Significant changes in plant architecture were during domestication of grain legumes. Many wild relatives of legumes are characterized by an indeterminate growth habit type, cultivated plants are characterized by indeterminate and determinate types. In plants with a determinate growth habit type, terminal inflorescence is formed at transition from the vegetative phase to the reproductive phase. These plants are characterized by a complex of features: simultaneous maturation of beans, resistance to lodging, etc. In indeterminate type of growth habit, the apical shoot meristem remains active during plant life. The main genes responsible for the plant transition to flowering are the homologs of the Arabidopsis genes LFY, TFL1, AP1. TFL1 gene is responsible for maintenance of growth of the shoot apical meristem; its homologs were identified in pea (PsTFL1a), soybean (Dt1/GmTFL1), common bean (PvTFL1y), cowpea (VuTFL1). The identification and characterization of the genes responsible for the type of stem growth habit are necessary for the successful selection of modern varieties suitable for mechanized cultivation. Design of molecular markers that diagnose this important breeding trait at early plant development stages, will help to determine the type of stem growth habit.

Flowering in Persian walnut: patterns of gene expression during flower development

BackgroundFlower development and sufficient fruit set are important parameters with respect to walnut yield. Knowledge about flowering genes of fruit trees can help to conduct better molecular breeding programs. Therefore, this study was carried out to investigate the expression pattern of some flowering genes (FT, SOC1, CAL, LFY and TFL1) in Persian walnut (cv. Chandler) during the growing season and winter dormancy.ResultsThe results showed that walnut flower induction and initiation in Shahmirzad, Iran occurred in early June and late September, respectively. After meeting chilling and heat requirement, flower differentiation and anthesis occurred in late-March and mid-April to early-May, respectively. Study of flowering gene expression showed that the expression of the FT gene increased in three stages including before breaking of bud dormancy, from late March to late April (coincided with flower differentiation and anthesis) and from late May to mid-June (coincided with flower induction). Like FT, the expression of SOC1 gene increased during flower induction and initiation (mid-May to early-August) as well as flower anthesis (mid-April to early-May). LFY and CAL genes as floral meristem identity genes are activated by FT and SOC1 genes. In contrast with flowering stimulus genes, TFL1 showed overexpression during winter dormancy which prevented flowering.ConclusionThe expression of FT gene activated downstream floral meristem identity genes including SOC1, CAL and LFY which consequently led to release bud dormancy as well as flower anthesis and induction. Also, TFL1 as a flowering inhibitor gene in walnut showed overexpression during the bud dormancy. Chilling accumulation reduced TFL1 gene expression and increased the expression of flowering genes which ultimately led to overcome dormancy.

The Floral Repressor GmFLC-like Is Involved in Regulating Flowering Time Mediated by Low Temperature in Soybean

Soybean is an important crop that is grown worldwide. Flowering time is a critical agricultural trait determining successful reproduction and yields. For plants, light and temperature are important environmental factors that regulate flowering time. Soybean is a typical short-day (SD) plant, and many studies have elucidated the fine-scale mechanisms of how soybean responds to photoperiod. Low temperature can delay the flowering time of soybean, but little is known about the detailed mechanism of how temperature affects soybean flowering. In this study, we isolated GmFLC-like from soybean, which belongs to the FLOWERING LOCUS C clade of the MADS-box family and is intensely expressed in soybean leaves. Heterologous expression of GmFLC-like results in a delayed-flowering phenotype in Arabidopsis. Additional experiments revealed that GmFLC-like is involved in long-term low temperature-triggered late flowering by inhibiting FT gene expression. In addition, yeast one-hybrid, dual-luciferase reporter assay, and electrophoretic mobility shift assay revealed that the GmFLC-like protein could directly repress the expression of FT2a by physically interacting with its promoter region. Taken together, our results revealed that GmFLC-like functions as a floral repressor involved in flowering time during treatments with various low temperature durations. As the only the FLC gene in soybean, GmFLC-like was meaningfully retained in the soybean genome over the course of evolution, and this gene may play an important role in delaying flowering time and providing protective mechanisms against sporadic and extremely low temperatures.

Soybean adaption to high-latitude regions is associated with natural variations of GmFT2b, an ortholog of FLOWERING LOCUS T.

ABSTRACTDay length has an important influence on flowering and growth habit in many plant species. In crops such as soybean, photoperiod sensitivity determines the geographical range over which a given cultivar can grow and flower. The soybean genome contains ~10 genes homologous to FT, a central regulator of flowering from Arabidopsis thaliana. However, the precise roles of these soybean FTs are not clearly. Here we show that one such gene, GmFT2b, promotes flowering under long‐days (LDs). Overexpression of GmFT2b upregulates expression of flowering‐related genes which are important in regulating flowering time. We propose a ‘weight’ model for soybean flowering under short‐day (SD) and LD conditions. Furthermore, we examine GmFT2b sequences in 195 soybean cultivars, as well as flowering phenotypes, geographical distributions and maturity groups. We found that Hap3, a major GmFT2b haplotype, is associated with significantly earlier flowering at higher latitudes. We anticipate our assay to provide important resources for the genetic improvement of soybean, including new germplasm for soybean breeding, and also increase our understanding of functional diversity in the soybean FT gene family.

Regulatory function of EARLI1-LIKE HYBRID PROLINE-RICH PROTEIN 1 in the floral transition of Arabidopsis thaliana

The plasma membrane- and endoplasmic reticulum-localized proteins encoded by the EARLI1 (EARLY ARABIDOPSIS ALUMINUM INDUCED 1) subfamily of genes contain a signal peptide, a proline-rich domain and an eight-cysteine motif. We previously showed that knockdown of EARLI1 subfamily genes in the late-flowering background of Col-FRI-Sf2 accelerates flowering time, suggesting that EARLI1 genes participate in maintenance of vegetative growth and prevention of premature reproductive growth. We show here that ELHyPRP1 (EARLI1-LIKE HYBRID PROLINE-RICH PROTEIN 1, AT4G12490), a member of this subfamily, is induced by environmental factors such as cold and long-day photoperiod. Detailed analyses with RNA interference and overexpressing lines demonstrated that modulation of ELHyPRP1 can affect the expression of photoperiod, vernalization, gibberellin, age, and autonomous flowering pathway genes. When ELHyPRP1 and other EARLI1 subfamily genes were silenced by RNA interference, most genes participating in the promotion of flowering were activated, while suppressors of the floral transition were repressed. Downregulation of ELHyPRP1 leads to increased expression of the flowering time genes FT and SOC1, and enhanced circadian expression patterns of genes associated with the promotion of the floral transition. Together with the silencing of ELHyPRP1, the flowering repressor FLC and the GA signalling repressor RGA were inhibited. ELHyPRP1 transgenic tobacco plants displayed late-flowering phenotypes and their flowering time was remarkably delayed in comparison to the wild-type Qinyan 95 tobacco plants grown under long-day photoperiod. These results indicate that ELHyPRP1 may be involved in balancing biomass accumulation and seed proliferation.

Identification of Brassica oleracea orthologs of the PEBP family and their expression patterns in curd development and flowering in cauliflower

The PEBP family members are reported to play important roles in plant flowering and reproductive organ formation. However, this gene family has not been identified nor their functions have been analyzed in Brassica oleracea. In this study, 10 PEBP genes were identified in the B. oleracea genome. These genes were categorized as TFL1, FT and MFT subfamilies according to the phylogeny and gene structure analysis. All the 10 PEBP genes were randomly distributed on seven of the nine chromosomes in B. oleracea. The expression profiles of the 10 PEBP genes in different tissues of cauliflower were evaluated through quantitative Real-Time polymerase chain reaction (qRT-PCR), and we found that FT and TFL1 genes tend to be expressed in reproductive organs and at high levels in the meristem, whereas the MFT genes showed no or very low expression in all tested tissues. Notably, the five TFL1 genes might be sub-functionalized in cauliflower. Bol026421 and Bol032920 were specifically expressed in SAMbr, maintaining the indeterminate growth of shoot apical meristem, whereas the other three genes (Bol015337, Bol005471 and Bol010027) were highly expressed in curd stages. Highly expressed TFL1 group genes with low mRNA levels of the flowering-promoting genes (FT, TSF), might be one of the important reasons of curd formation in cauliflower. Generally, the results obtained in this study will help further studies on the roles of PEBP genes during curd development and flowering initiation, leading to crop improvement.

Overexpression of Medicago MtCDFd1_1 Causes Delayed Flowering in Medicago via Repression of MtFTa1 but Not MtCO-Like Genes.

Optimizing flowering time is crucial for maximizing crop productivity, but gaps remain in the knowledge of the mechanisms underpinning temperate legume flowering. Medicago, like winter annual Arabidopsis, accelerates flowering after exposure to extended cold (vernalization, V) followed by long-day (LD) photoperiods. In Arabidopsis, photoperiodic flowering is triggered through CO, a photoperiodic switch that directly activates the FT gene encoding a mobile florigen and potent activator of flowering. In Arabidopsis, several CYCLING DOF FACTORs (CDFs), including AtCDF1, act redundantly to repress CO and thus FT expression, until their removal in LD by a blue-light-induced F-BOX1/GIGANTEA (FKF1/GI) complex. Medicago possesses a homolog of FT, MtFTa1, which acts as a strong activator of flowering. However, the regulation of MtFTa1 does not appear to involve a CO-like gene. Nevertheless, work in pea suggests that CDFs may still regulate flowering time in temperate legumes. Here, we analyze the function of Medicago MtCDF genes with a focus on MtCDFd1_1 in flowering time and development. MtCDFd1_1 causes strong delays to flowering when overexpressed in Arabidopsis and shows a cyclical diurnal expression in Medicago with peak expression at dawn, consistent with AtCDF genes like AtCDF1. However, MtCDFd1_1 lacks predicted GI or FKF1 binding domains, indicating possible differences in its regulation from AtCDF1. In Arabidopsis, CDFs act in a redundant manner, and the same is likely true of temperate legumes as no flowering time phenotypes were observed when MtCDFd1_1 or other MtCDFs were knocked out in Medicago Tnt1 lines. Nevertheless, overexpression of MtCDFd1_1 in Medicago plants resulted in late flowering relative to wild type in inductive vernalized long-day (VLD) conditions, but not in vernalized short days (VSDs), rendering them day neutral. Expression of MtCO-like genes was not affected in the transgenic lines, but LD-induced genes MtFTa1, MtFTb1, MtFTb2, and MtSOC1a showed reduced expression. Plants carrying both the Mtfta1 mutation and 35S:MtCDFd1_1 flowered no later than the Mtfta1 plants. This indicates that 35S:MtCDFd1_1 likely influences flowering in VLD via repressive effects on MtFTa1 expression. Overall, our study implicates MtCDF genes in photoperiodic regulation in Medicago by working redundantly to repress FT-like genes, particularly MtFTa1, but in a CO-independent manner, indicating differences from the Arabidopsis model.

The role of jasmonate signaling pathway in plant’s flowering genes response to ionizing radiation

Aim. This study aimed to characterize the role of the jasmonate signaling pathway in flowering genes response to acute and chronic ionizing irradiation in plants. Methods. We used the wild-type Arabidopsis thaliana and jasmonic pathway defective jin mutant of Col0 ecotype in our experiments. The chronic irradiation was provided by 137СsCl with a total dose of 17 cGy and a dose rate of 6.8×10-6 cGy/s. The acute irradiation experiment was performed on 21 days old plants at the 5.0 stage (Boyes 2001) by X-rays in a total dose of 5 Gy with a dose rate of 89 cGy/s. The length of stems and leaves was measured in post-irradiation period. The molecular genetic analysis was done using real-time PCR. We determined the relative expression of key flowering genes AP1, GI, FT, CO, ACT2 with UBQ10 used as reference genes. Statistical analysis of phenotypic parameters was done using Student’s t-test in GraphPad Prism 8 software. The quantitative PCR data were analyzed in the REST 2009 software, QIAGEN. Results. The plant groups differed significantly by the stem length (p>0,05). The study revealed decreased expression of CO, GI and FT genes in jin mutants. The overexpression of AP1 in jin mutants under chronic irradiation may cause cell division errors and impact flower development. In contrast, AP1 expression in WT plants was near to normal =1 under chronic irradiation. These results suggest the involvement of the jasmonate pathway in the regulation of plants flowering during the irradiation. Сonclusion. Based on the results of our study, we hypothesize that jasmonic acid has a stabilizing effect on the rate of cell differentiation in plants under chronic irradiation. Despite the uncovered role of jasmonic acid in Arabidopsis thaliana flowering the exact mechanism of its action remains unclear and requires further investigation.Keywords: jasmonate signaling, jasmonic acid, JA, flowering, ionizing radiation, real-time PCR, relative expression.

Altered Expression of an FT Cluster Underlies a Major Locus Controlling Domestication-Related Changes to Chickpea Phenology and Growth Habit.

Flowering time is a key trait in breeding and crop evolution, due to its importance for adaptation to different environments and for yield. In the particular case of chickpea, selection for early phenology was essential for the successful transition of this species from a winter to a summer crop. Here, we used genetic and expression analyses in two different inbred populations to examine the genetic control of domestication-related differences in flowering time and growth habit between domesticated chickpea and its wild progenitor Cicer reticulatum. A single major quantitative trait locus for flowering time under short-day conditions [Days To Flower (DTF)3A] was mapped to a 59-gene interval on chromosome three containing a cluster of three FT genes, which collectively showed upregulated expression in domesticated relative to wild parent lines. An equally strong association with growth habit suggests a pleiotropic effect of the region on both traits. These results indicate the likely molecular explanation for the characteristic early flowering of domesticated chickpea, and the previously described growth habit locus Hg. More generally, they point to de-repression of this specific gene cluster as a conserved mechanism for achieving adaptive early phenology in temperate legumes.

Epigenetic regulation of miR396 expression by SWR1-C and the effect of miR396 on leaf growth and developmental phase transition in Arabidopsis.

In this study, we investigated the regulatory function of miR396 in the phase transition in Arabidopsis thaliana. Using AtMIR396a/b knockout mutants generated through clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9)-directed genome editing, we showed that miR396 negatively regulates the leaf size and vegetative phase transition, and the first leaf with abaxial trichomes appeared earlier in the mir396ab double mutant than in the wild type (WT) and was significantly delayed in miR396 overexpression lines. Moreover, mir396ab exhibited early flowering, whereas 35S:MIR396a/b and cib4-1 delayed flowering, and the flowering time was negatively correlated with FT gene expression. Furthermore, in arp6 and pie1 mutants, which are deficient in the ATP-dependent chromatin remodeling complex (SWR1-C), miR396 expression was significantly repressed. Compared with the WT, reduced H2A.Z deposit and stronger relative nucleosome occupancy in the promoter region of MIR396a was found in the arp6 mutant, indicating that SWR1-C contributes to the transcriptional activation of MIR396a via nucleosome dynamics. In addition, miR396 displayed specific spatio-temporal expression patterns in the leaf, which was altered in arp6 and pie1, and therefore affected the transcript levels of CIB4 and FT in these mutants. We propose that miR396 is not only a marker of cell differentiation, but also an age signal for leaf development and phase change. Meanwhile, SWR1-C-mediated epigenetic regulation contributes to the age-dependent enhancement of miR396 expression and differential miR396 accumulation among leaves.

A single residue change in the product of the chrysanthemum gene TPL1-2 leads to a failure in its repression of flowering

The TPL/TPR co-repressor is involved in many plant signaling pathways, including those regulating the switch from vegetative to reproductive growth. Here, a TPL homolog (TPL 1-2) was isolated from chrysanthemum. Its product was found to be deposited in the nucleus. The abundance of TPL1-2 transcript varied across the plant, with its highest level being recorded in the stem apex, and its lowest in the root and stem. In the leaf, the abundance of TPL1-2 transcript was highest at dusk in plants exposed to long days, and at dawn in those exposed to short days. Site-directed mutagenesis was used to induce an N176H mutation in TPL1-2. The constitutive expression in Arabidopsis thaliana of the wild type and the mutated alleles of TPL1-2 had a contrasting effect on flowering time, with the mutant transgene expressors flowering later than the wild type transgene expressors. The flowering-related genes FT, TSF, FUL and AP1 were all more strongly transcribed in the mutant transgene expressors than in the wild type transgene expressors.

Nitrate Transporter 1.1 is involved in regulating flowering time via transcriptional regulation of FLOWERING LOCUS C in Arabidopsis thaliana

Nitrate Transporter 1.1 (NRT1.1) is a nitrate transporter and sensor that modulates plant metabolism and growth. It has previously been shown that NRT1.1 is involved in the regulation of flowering time in Arabidopsis thaliana. In this study, we mainly used genetic and molecular methods to reveal the key flowering pathway that NRT1.1 may be involved in. Mutant alleles of CO and FLC, two crucial components in the flowering pathway, were introduced into the NRT1.1 defective mutant background by crossing. When the CO mutation was introduced into chl1-5 plants, the double mutant had delayed flowering time, and the CO transcription levels did not change in the chl1-5 plants. These results indicate that the CO-dependent photoperiod may be not associated with the delayed flowering shown by chl1-5. However, FLC loss of function could rescue the late flowering phenotype of the chl1-5 mutant, and FLC expression levels significantly increased in the NRT1.1 defective mutant plants. The FT expression levels in the chl1-5flc-3 double mutant plants recovered when the FLC mutation was introduced into chl1-5 plants and the up-regulation of FLC transcripts in the chl1-5 mutant plants was not related to nitrate availability. Our findings suggest that NRT1.1 affects flowering time via interaction with the FLC-dependent flowering pathway to influence its target gene FT, and that NRT1.1 may be included in an additional signaling pathway that represses the expression of FLC in a nitrate-independent manner.

Differential expression of flowering genes in Arabidopsis thaliana under chronic and acute ionizing radiation

Purpose: Chronic and acute irradiations have drastic effects on flowering stage that plays an important role in further seed development and can determine seed yield. The expression of the key flowering genes, AP1, CO, GI, FT, FLC, and LFY, sensitive to irradiation repair gene RAD51 and the proliferation gene PCNA2 were studied in the wild-type Arabidopsis thaliana (Columbia ecotype) under chronic and acute irradiations.Materials and methods: Chronic irradiation was performed using the radioactive isotope 137СsCl in two total doses of 3 cGy and 17 cGy, with the dose rate of 10−7 cGy/s and 6.8 10−6 cGy/s, respectively. The plants were grown under chronic irradiation during 6 weeks, from seeds till the 6.3 stage of flowering. For acute exposure, the plants were X-ray irradiated one time at the 5.0 development stage (20 days old) by a total dose of 15 Gy with the dose rate of 89 cGy/s.Results: After chronic irradiation with the 3 cGy dose the irradiated plants demonstrated 8 ± 2.8 days earlier flowering than in the control group. However, at the 17 cGy chronic and at the 15 Gy acute doses plants showed 14 ± 3.7 and 2 ± 1.4 days later flowering, respectively. The 3 cGy chronic exposure significantly increased the expression of the CO gene by a factor of 1.152 (1.087–1.217 95% C.I.) and decreased the expression of the FT gene by a factor of 0.128 (0.021–0.396 95% C.I.). The 17 cGy chronic exposure decreased expression of the AP1 gene by a factor of 0.872 (0.803–0.940 95% C.I.) and the LFY gene by a factor of 0.471 (0.306–0.687 95% C.I.). The 15 Gy acute exposure decreased the expression of the AP1 gene by a factor of 0.104 (0.074–0.144 95% C.I.) and the PCNA2 gene by a factor of 0.346 (0.238–0.488 95% C.I.).Conclusions: The increased expression of the CO gene and decreased expression of the AP1 and FT genes under the lower dose of chronic exposure were associated with earlier flowering. The acute exposure increased the expression of the PCNA2 gene and decreased the expression of the flowering genes, except AP1. The flowering was delayed under both the higher dose of chronic exposure and under acute exposure, but it was less affected by the latter. Presumably, it was related to the activation of DNA repair under the 3 cGy chronic and 15 Gy acute irradiations.

Isolation and functional characterization of a novel FLOWERING LOCUS T homolog (NtFT5) in Nicotiana tabacum

The phosphatidyl ethanolamine-binding proteins (PEBPs) function primarily in regulating flowering in plants. Here, we report a genome-wide identification of PEBPs and functional characterization of a novel FLOWERING LOCUS T homolog (NtFT5) in tobacco, Nicotiana tabacum. Seven new PEBPs were identified by a genome-wide analysis from N. tabacum. Expression profile showed that NtFT5 was mainly expressed in flowers. Overexpression of NtFT5 conferred an early flowering phenotype. By optimizing rooting medium, heritable short life-cycle tobacco lines were obtained by overexpression of NtFT5. Several orthologs of flowering genes downstream of FT gene were up-regulated in the NtFT5-overexpression transgenic plant lines. The NtFT5-overexpressing tobaccos formed fewer flowers and seeds per capsule compared with wild type. The seed-to-seed life cycle of NtFT5 overexpressing tobacco lines was about 2.5 months. Gene identification was effectively undertaken in the short life-cycle tobacco line by a second transformation via a gusA reporter gene and transient expression of Ros1 via PVX (Potato Virus X)system. Our findings indicate that NtFT5 is a novel FT homolog that has potential to induce flowering, which will improve our understanding of the mechanism underlying flowering control in N. tabacum. In addition, the results show that the generated heritable short life-cycle transgenic tobacco line is an effective and stable host system to accelerate gene function study, which promises to provide a better tobacco research model for plants.