TFL1-like Genes Research Articles

Shade signals activate distinct molecular mechanisms that induce dormancy and inhibit flowering in vegetative axillary buds of sorghum.

Shoot branches grow from axillary buds and play a crucial role in shaping shoot architecture and determining crop yield. Shade signals inactivate phytochrome B (phyB) and induce bud dormancy, thereby inhibiting shoot branching. Prior transcriptome profiling of axillary bud dormancy in a phyB-deficient mutant (58M, phyB-1) and bud outgrowth in wild-type (100M, PHYB) sorghum genotypes identified differential expression of genes associated with flowering, plant hormones, and sugars, including SbCN2, SbNCED3, SbCKX1, SbACO1, SbGA2ox1, and SbCwINVs. This study examined the expression of these genes during bud dormancy induced by shade and defoliation in 100M sorghum. The aim was to elucidate the molecular mechanisms activated by shade in axillary buds by comparing them with those activated by defoliation. The expression of marker genes for sugar levels suggests shade and defoliation reduce the sugar supply to the buds and induce bud dormancy. Intriguingly, both shade signals and defoliation downregulated SbNCED3, suggesting that ABA might not play a role in promoting axillary bud dormancy in sorghum. Whereas the cytokinin (CK) degrading gene SbCKX1 was upregulated solely by shade signals in the buds, the CK inducible genes SbCGA1 and SbCwINVs were downregulated during both shade- and defoliation-induced bud dormancy. This indicates a decrease in CK levels in the dormant buds. Shade signals dramatically upregulated SbCN2, an ortholog of the Arabidopsis TFL1 known for inhibiting flowering, whereas defoliation did not increase SbCN2 expression in the buds. Removing shade temporarily downregulated SbCN2 in dormant buds, further indicating its expression is not always correlated with bud dormancy. Because shade signals also trigger a systemic early flowering signal, SbCN2 might be activated to protect the buds from transitioning to flowering before growing into branches. In conclusion, this study demonstrates that shade signals activate two distinct molecular mechanisms in sorghum buds: one induces dormancy by reducing CK and sugars, whereas the other inhibits flowering by activating SbCN2. Given the agricultural significance of TFL1-like genes, the rapid regulation of SbCN2 by light signals in axillary buds revealed in this study warrants further investigation to explore its potential in crop improvement strategies.

Evolution of FLOWERING LOCUS T-like genes in angiosperms: a core Lamiales-specific diversification.

Plant life history is determined by two transitions, germination and flowering time, in which the phosphatidylethanolamine-binding proteins (PEBPs) FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1) play key regulatory roles. Compared with the highly conserved TFL1-like genes, FT-like genes vary significantly in copy numbers in gymnosperms, and monocots within the angiosperms, while sporadic duplications can be observed in eudicots. Here, via a systematic analysis of the PEBPs in angiosperms with a special focus on 12 representative species featuring high-quality genomes in the order Lamiales, we identified a successive lineage-specific but systematic expansion of FT-like genes in the families of core Lamiales. The first expansion event generated FT1-like genes mainly via a core Lamiales-specific whole-genome duplication (cL-WGD), while a likely random duplication produced the FT2-like genes in the lineages containing Scrophulariaceae and the rest of the core Lamiales. Both FT1- and FT2-like genes were further amplified tandemly in some families. These expanded FT-like genes featured highly diverged expression patterns and structural variation, indicating functional diversification. Intriguingly, some core Lamiales contained the relict MOTHER OF FT AND TFL1 like 2 (MFT2) that probably expanded in the common ancestor of angiosperms. Our data showcase the highly dynamic lineage-specific expansion of the FT-like genes, and thus provide important and fresh evolutionary insights into the gene regulatory network underpinning flowering time diversity in Lamiales and, more generally, in angiosperms.

Functional characterization of three TERMINAL FLOWER 1-like genes from Platanus acerifolia.

TFL1-like genes of the basal eudicot Platanus acerifolia have conserved roles in maintaining vegetative growth and inhibiting flowering, but may act through distinct regulatory mechanism. Three TERMINAL FLOWER 1 (TFL1)-like genes were isolated and characterized from London plane tree (Platanus acerifolia). All genes have conserved genomic organization and characteristic of the phosphatidylethanolamine-binding protein (PEBP) family. Sequence alignment and phylogenetic analysis indicated that two genes belong to the TFL1 clade, designated as PlacTFL1a and PlacTFL1b, while another one was grouped in the BFT clade, named as PlacBFT. qRT-PCR analysis showed that all three genes primarily expressed in vegetative phase, but the expression of PlacTFL1a was much higher and wider than that of PlacTFL1b, with the latter only detected at relatively low expression levels in apical and lateral buds in April. PlacBFT was mainly expressed in young stems of adult trees followed by juvenile tissues. Ectopic expression of any TFL1-like gene in Arabidopsis showed phenotypes of delayed or repressed flowering. Furthermore, overexpression of PlacTFL1a gene in petunia also resulted in extremely delayed flowering. In non-flowering 35:PlacTFL1a transgenic petunia plants, the FT-like gene (PhFT) gene was significantly upregulated and AP1 homologues PFG, FBP26 and FBP29 were significantly down-regulated in leaves. Yeast two-hybrid analysis indicated that only weak interactions were detected between PlacTFL1a and PlacFDL, and PlacTFL1a showed no interaction with PhFDL1/2. These results indicated that the TFL1-like genes of Platanus have conserved roles in repressing flowering, but probably via a distinct regulatory mechanism.

Genome-wide identification and characterization profile of phosphatidy ethanolamine-binding protein family genes in carrot.

Members of the family of Phosphatidy Ethanolamine-Binding Protein (PEBP) have been shown to be key regulators of the transition of plants from vegetative to reproductive phases. Here, a total of 12 PEBP proteins were identified in the carrot (Daucus carota L.) genome and classified into FT-like (4), TFL1-like (6), and MFT-like 2) subfamilies, that had different lengths (110-267 aa) and were distributed unevenly across seven chromosomes. Moreover, 13 and 31 PEBP proteins were identified in other two Apiaceae species, celery (Apium graveolens L.) and coriander (Coriandrum sativum L.). The phylogenetic and evolutionary results of these PEBP family proteins were obtained based on the protein sequences. In the three Apiaceae species, purifying selection was the main evolutionary force, and WGD, segmental duplication, and dispersed duplication have played key roles in the PEBP family expansion. The expression analysis showed that carrot PEBP genes exhibited relatively broad expression patterns across various tissues. In the period of bolting to flowering, the carrot FT-like subfamily genes were upregulated as positive regulators, and TFL1-like subfamily genes remained at lower expression levels as inhibitors. More interestingly, the members of carrot FT-like genes had different temporal-spatial expression characteristics, suggesting that they have different regulatory functions in the carrot reproductive phase. In summary, this study contributes to our understanding of the PEBP family proteins and provides a foundation for exploring the mechanism of carrot bolting and flowering for the breeding of cultivars with bolting resistance.

Antisense Expression of Apple TFL1-like Gene (MdTFL1) Promotes Early Flowering and Causes Phenotypic Changes in Tobacco

Apples (Malus × domestica Borkh.) require up to several years for flowering and bearing fruits. The transition from vegetative to reproductive phase is controlled by floral regulators such as TERMINAL FLOWER 1 (TFL1) and FLOWERING LOCUS T (FT). TFL1 mediates the maintenance of vegetative phase, unlike the antagonistic function of FT to promote the transition into reproductive phase. In this study, we isolated apple TFL1-like gene (MdTFL1) to elucidate various phenotypic traits triggered by the antisense expression of MdTFL1 in tobacco apart from its floral induction function. Early flowering was observed in the tobacco line with MdTFL1 knockout, indicating the reduced time for transition to vegetative phases. Quantitative reverse-transcription PCR showed upregulation of genes involved in the regulation of floral induction, including NtAP1, NtSOC1, NFL1, and NtFTs, and downregulation of carotenoid cleavage dioxygenases (CCDs) and CEN-like genes in transgenic lines. Interestingly, transgenic tobacco expressing antisense MdTFL1 exhibited distinct morphological changes in lateral shoot outgrowth, internode length, and the development of leaves, flowers, and fruits. The results suggested that using the antisense expression of MdTFL1 gene is one of the approaches to shorten the vegetable phase and proposed improvement of plant architecture in horticultural crops.

Rice SEPALLATA genes OsMADS5 and OsMADS34 cooperate to limit inflorescence branching by repressing the TERMINAL FLOWER1-like gene RCN4.

The spatiotemporal control of meristem identity is critical for determining inflorescence architecture, and thus yield, of cereal plants. However, the precise mechanisms underlying inflorescence and spikelet meristem determinacy in cereals are still largely unclear. We have generated loss-of-function and overexpression mutants of the paralogous OsMADS5 and OsMADS34 genes in rice (Oryza sativa), and analysed their panicle phenotypes. Using chromatin immunoprecipitation, electrophoretic mobility-shift and dual-luciferase assays, we have also identified RICE CENTRORADIALIS 4 (RCN4), a TFL1-like gene, as a direct downstream target of both OsMADS proteins, and have analysed RCN4 mutants. The osmads5 osmads34 mutant lines had significantly enhanced panicle branching with increased secondary, and even tertiary and quaternary, branches, compared to wild-type (WT) and osmads34 plants. The osmads34 mutant phenotype could largely be rescued by also knocking out RCN4. Moreover, transgenic panicles overexpressing RCN4 had significantly increased branching, and initiated development of c. 7× more spikelets than WT. Our results reveal a role for OsMADS5 in panicle development, and show that OsMADS5 and OsMADS34 play similar functions in limiting branching and promoting the transition to spikelet meristem identity, in part by repressing RCN4 expression. These findings provide new insights to better understand the molecular regulation of rice inflorescence architecture.

Identification of apple TFL1-interacting proteins uncovers an expanded flowering network

MdTFL1, a floral repressor, forms protein complexes with several proteins and could compete with MdFT1 to regulate reproductive development in apple. Floral transition is a key developmental stage in the annual growth cycle of perennial fruit trees that directly determines the fruit development in the subsequent stage. FLOWERING LOCUS T (FT)/TERMINAL FLOWER1 (TFL1) family is known to play a vital regulatory role in plant growth and flowering. In apple, the two TFL1-like genes (MdTFL1-1 and MdTFL1-2) function as floral inhibitors; however, their mechanism of action is still largely unclear. This study aimed to functionally validate MdTFL1 and probe into its mechanism of action in apple. MdTFL1-1 and MdTFL1-2 were expressed mainly in stem and apical buds of vegetative shoots, with little expression in flower buds and young fruit. Expression of MdTFL1-1 and MdTFL1-2 rapidly decreased during floral induction. On the other hand, transgenic Arabidopsis, which ectopically expressed MdTFL1-1 or MdTFL1-2, flowered later than wild-type plants; demonstrating their in planta capability to function redundantly as flower repressors. Furthermore, we identified hundreds of novel interaction proteins of the two apple MdTFL1 proteins using yeast two-hybrid screens. Independent experiments for several proteins confirmed the yeast two-hybrid interactions. Among them, the transcription factor Nuclear Factor-Y subunit C (MdNF-YC2) functions as a promoter of flowering in Arabidopsis by activating LEAFY (LFY) and APETALA1 (AP1) expression. MdFT1 showed a similar interaction pattern as MdTFL1, implying a possible antagonistic action in the regulation of flowering. These newly identified TFL1-interacting proteins (TIPs) not only expand the floral regulatory network, but may also introduce new roles for TFL1 in plant development.

Structural organization of <em>TFL1</em>-like genes in representatives of the tribe Phaseoleae DC.

The type of stem growth is one of the key features in determining plant architectonics. Stem growth type is an economically important trait. It interconnects with stem length, flowering duration, yield, resistance to lodging, and suitability of mechanized cultivation. Mutations in the TFL1 gene and its homologs have been demonstrated to change meristem indeterminacy across genera. The aim of this work was to characterize and compare the structural organization of TFL1-like genes in representatives of the tribe Phaseoleae (pigeonpea Cajanus cajan, soybean Glycine max, common bean Phaseolus vulgaris, adzuki bean Vigna angularis, mung bean V. radiata, and cowpea V. unguiculata) based on in silico analysis, including analysis of nucleotide sequences, predicted elements in promoter regions, predicted amino acid sequences, putative functional domains and 3D protein structures. We investigated TFL1 (one gene for adzuki bean, four copies for soybean, two copies for other studied species), ATC (two copies for soybean, one gene for other investigated species), and BFT (two copies for soybean, one gene for other studied species) gene family members found in whole-genome sequences databases available for representatives of the tribe Phaseoleae. The presence of duplicated copies for all genes in soybean may be a result of the last genome duplication event during the evolution of this species. Duplication of TFL1 gene to two copies in most of studied species of the tribe Phaseoleae is probably accompanied by the maintenance of the functional state of these genes. The exception is VrTFL1.2 of V. radiata, which likely had lost its functionality. This work broadens the existing data about the number of gene copies, their structural divergence and evolution, and the expected functional differences. This information will be important for understanding the molecular genetic mechanisms underlying the maintenance of indeterminacy in the growth of the shoot apical meristem, as well as in the control of the transition to the reproductive phase of plant development.

Genome-wide characterization of PEBP family genes in nine Rosaceae tree species and their expression analysis in P. mume

BackgroundPhosphatidylethanolamine-binding proteins (PEBPs) constitute a common gene family found among animals, plants and microbes. Plant PEBP proteins play an important role in regulating flowering time, plant architecture as well as seed dormancy. Though PEBP family genes have been well studied in Arabidopsis and other model species, less is known about these genes in perennial trees.ResultsTo understand the evolution of PEBP genes and their functional roles in flowering control, we identified 56 PEBP members belonging to three gene clades (MFT-like, FT-like, and TFL1-like) and five lineages (FT, BFT, CEN, TFL1, and MFT) across nine Rosaceae perennial species. Structural analysis revealed highly conserved gene structure and protein motifs among Rosaceae PEBP proteins. Codon usage analysis showed slightly biased codon usage across five gene lineages. With selection pressure analysis, we detected strong purifying selection constraining divergence within most lineages, while positive selection driving the divergence of FT-like and TFL1-like genes from the MFT-like gene clade. Spatial and temporal expression analyses revealed the essential role of FT in regulating floral bud breaking and blooming in P. mume. By employing a weighted gene co-expression network approach, we inferred a putative FT regulatory module required for dormancy release and blooming in P. mume.ConclusionsWe have characterized the PEBP family genes in nine Rosaceae species and examined their phylogeny, genomic syntenic relationship, duplication pattern, and expression profiles during flowering process. These results revealed the evolutionary history of PEBP genes and their functions in regulating floral bud development and blooming among Rosaceae tree species.

RICE CENTRORADIALIS 1, a TFL1-like Gene, Responses to Drought Stress and Regulates Rice Flowering Transition

BackgroundThe initiation of flowering transition in rice (Oryza sativa) is a complex process regulated by genes and environment. In particular, drought can interfere with flowering; therefore, many plants hasten this process to shorten their life cycle under water scarcity, and this is known as drought-escape response. However, rice has other strategies; for example, drought stress can delay flowering instead of accelerating it. RICE CENTRORADIALIS 1 (RCN1) is a TERMINAL FLOWER-like gene that influences rice flowering transition and spike differentiation. It interacts with 14–3-3 proteins and transcription factor OsFD1 to form a florigen repression complex that suppresses flowering transition in rice.ResultsIn this study, we explored the role of RCN1 in the molecular pathway of drought-regulated flowering transition. The rcn1 mutant plants displayed early heading under both normal water and drought stress conditions, and they were more insensitive to drought stress than the wild-type plants. Abscisic acid (ABA) signaling-mediated drought-induced RCN1 is involved in this process.ConclusionsThus, RCN1 plays an important role in the process of drought stress inhibiting flowering transition. It may worked by suppressing the protein function rather than transcription of HEADING DATE 3a.

EjTFL1 Genes Promote Growth but Inhibit Flower Bud Differentiation in Loquat.

TERMINAL FLOWER1 (TFL1), a key factor belonging to the phosphatidyl ethanolamine-binding protein (PEBP) family, controls flowering time and inflorescence architecture in some plants. However, the role of TFL1 in loquat remains unknown. In this study, we cloned two TFL1-like genes (EjTFL1-1 and EjTFL1-2) with conserved deduced amino acid sequences from cultivated loquat (Eriobotrya japonica Lindl.). First, we determined that flower bud differentiation occurs at the end of June and early July, and then comprehensively analyzed the temporal and spatial expression patterns of these EjTFL1s during loquat growth and development. We observed the contrasting expression trends for EjTFL1s and EjAP1s (APETALA 1) in shoot apices, and EjTFL1s were mainly expressed in young tissues. In addition, short-day and exogenous GA3 treatments promoted the expression of EjTFL1s, and no flower bud differentiation was observed after these treatments in loquat. Moreover, EjTFL1s were localized to the cytoplasm and nucleus, and both interacted with another flowering transcription factor, EjFD, in the nucleus, and EjTFL1s-EjFD complex significantly repressed the promoter activity of EjAP1-1. The two EjTFL1s were overexpressed in wild-type Arabidopsis thaliana Col-0, which delayed flowering time, promoted stem elongation, increased the number of branches, and also affected flower and silique phenotypes. In conclusion, our results suggested that EjTFL1-1 and EjTFL1-2 do not show the same pattern of expression whereas both are able of inhibiting flower bud differentiation and promoting vegetative growth in loquat by integrating GA3 and photoperiod signals. These findings provide useful clues for analyzing the flowering regulatory network of loquat and provide meaningful references for flowering regulation research of other woody fruit trees.

Evolution and Expression of Reproductive Transition Regulatory Genes FT/TFL1 With Emphasis in Selected Neotropical Orchids.

Flowering is a rigorously timed and morphologically complex shift in plant development. This change depends on endogenous as well as environmental factors. FLOWERING LOCUS T (FT) integrates several cues from different pathways acting as a flowering promoter. Contrary to the role of FT, its paralog TERMINAL FLOWER 1 (TFL1) delays floral transition. Although FT/TFL1 homologs have been studied in model eudicots and monocots, scarce studies are available in non-model monocots like the Orchidaceae. Orchids are very diverse and their floral complexity is translated into a unique aesthetic display, which appeals the ornamental plant market. Nonetheless, orchid trade faces huge limitations due to their long vegetative phase and intractable indoor flowering seasons. Little is known about the genetic basis that control reproductive transition in orchids and, consequently, manipulating their flowering time remains a challenge. In order to contribute to the understanding of the genetic bases that control flowering in orchids we present here the first broad-scale analysis of FT/TFL1-like genes in monocots with an expanded sampling in Orchidaceae. We also compare expression patterns in three selected species and propose hypotheses on the putative role of these genes in their reproductive transition. Our findings show that FT-like genes are by far more diversified than TFL1-like genes in monocots with six subclades in the former and only one in the latter. Within MonFT1, the comparative protein sequences of MonFT1A and MonFT1B suggest that they could have recruited functional roles in delaying flowering, a role typically assigned to TFL1-like proteins. On the other hand, MonFT2 proteins have retained their canonical motifs and roles in promoting flowering transition. This is also shown by their increased expression levels from the shoot apical meristem (SAM) and leaves to inflorescence meristems (IM) and floral buds (FBs). Finally, TFL1-like genes are retained as single copy and often times are lost. Their loss could be linked to the parallel recruitment of MonFT1A and MonFT1B homologs in delaying flowering and maintaining indeterminacy of the inflorescence meristem. These hypotheses lay the foundation for future functional validation in emerging model orchid species and comparative analyses in orchids with high horticultural potential in the market.

Genetic mechanisms in the repression of flowering by gibberellins in apple (Malus x domestica Borkh.)

BackgroundGibberellins (GAs) can have profound effects on growth and development in higher plants. In contrast to their flowering-promotive role in many well-studied plants, GAs can repress flowering in woody perennial plants such as apple (Malus x domestica Borkh.). Although this effect of GA on flowering is intriguing and has commercial importance, the genetic mechanisms linking GA perception with flowering have not been well described.ResultsApplication of a mixture of bioactive GAs repressed flower formation without significant effect on node number or shoot elongation. Using Illumina-based transcriptional sequence data and a newly available, high-quality apple genome sequence, we generated transcript models for genes expressed in the shoot apex, and estimated their transcriptional response to GA. GA treatment resulted in downregulation of a diversity of genes participating in GA biosynthesis, and strong upregulation of the GA catabolic GA2 OXIDASE genes, consistent with GA feedback and feedforward regulation, respectively. We also observed strong downregulation of numerous genes encoding potential GA transporters and receptors. Additional GA-responsive genes included potential components of cytokinin (CK), abscisic acid (ABA), brassinosteroid, and auxin signaling pathways. Finally, we observed rapid and strong upregulation of both of two copies of a gene previously observed to inhibit flowering in apple, MdTFL1 (TERMINAL FLOWER 1).ConclusionThe rapid and robust upregulation of genes associated with GA catabolism in response to exogenous GA, combined with the decreased expression of GA biosynthetic genes, highlights GA feedforward and feedback regulation in the apple shoot apex. The finding that genes with potential roles in GA metabolism, transport and signaling are responsive to GA suggests GA homeostasis may be mediated at multiple levels in these tissues. The observation that TFL1-like genes are induced quickly in response to GA suggests they may be directly targeted by GA-responsive transcription factors, and offers a potential explanation for the flowering-inhibitory effects of GA in apple. These results provide a context for investigating factors that may transduce the GA signal in apple, and contribute to a preliminary genetic framework for the repression of flowering by GAs in a woody perennial plant.

Cotton CENTRORADIALIS/TERMINAL FLOWER 1/SELF-PRUNING genes functionally diverged to differentially impact plant architecture

Genes of the CENTRORADIALIS/TERMINAL FLOWER 1/SELF-PRUNING (CETS) family influence meristem identity by controlling the balance between indeterminate and determinate growth, thereby profoundly impacting plant architecture. Artificial selection during cotton (Gossypium hirsutum) domestication converted photoperiodic trees to the day-neutral shrubs widely cultivated today. To understand the regulation of cotton architecture and exploit these principles to enhance crop productivity, we characterized the CETS gene family from tetraploid cotton. We demonstrate that genes of the TERMINAL FLOWER 1 (TFL1)-like clade show different roles in regulating growth patterns. Cotton has five TFL1-like genes: SELF-PRUNING (GhSP) is a single gene whereas there are two TFL1-like and BROTHER OF FT (BFT)-like genes, and these duplications are specific to the cotton lineage. All genes of the cotton TFL1-like clade delay flowering when ectopically expressed in transgenic Arabidopsis, with the strongest phenotypes failing to produce functional flowers. GhSP, GhTFL1-L2, and GhBFT-L2 rescue the early flowering Attfl1-14 mutant phenotype, and the encoded polypeptides interact with a cotton FD protein. Heterologous promoter::GUS fusions illustrate differences in the regulation of these genes, suggesting that genes of the GhTFL1-like clade may not act redundantly. Characterizations of the GhCETS family provide strategies for nuanced control of plant growth.

Functional divergence and intron variability during evolution of angiosperm TERMINAL FLOWER1 (TFL1) genes

The protein encoded by the TERMINAL FLOWER1 (TFL1) gene maintains indeterminacy in inflorescence meristem to repress flowering, and has undergone multiple duplications. However, basal angiosperms have one copy of a TFL1-like gene, which clusters with eudicot TFL1/CEN paralogs. Functional conservation has been reported in the paralogs CENTRORADIALIS (CEN) in eudicots, and ROOTS CURL IN NPA (RCNs) genes in monocots. In this study, long-term functional conservation and selective constraints were found between angiosperms, while the relaxation of selective constraints led to subfunctionalisation between paralogs. Long intron lengths of magnoliid TFL1-like gene contain more conserved motifs that potentially regulate TFL1/CEN/RCNs expression. These might be relevant to the functional flexibility of the non-duplicate TFL1-like gene in the basal angiosperms in comparison with the short, lower frequency intron lengths in eudicot and monocot TFL1/CEN/RCNs paralogs. The functionally conserved duplicates of eudicots and monocots evolved according to the duplication-degeneration-complementation model, avoiding redundancy by relaxation of selective constraints on exon 1 and exon 4. These data suggest that strong purifying selection has maintained the relevant functions of TFL1/CEN/RCNs paralogs on flowering regulation throughout the evolution of angiosperms, and the shorter introns with radical amino acid changes are important for the retention of paralogous duplicates.

The Evolution of the FT/TFL1 Genes in Amaranthaceae and Their Expression Patterns in the Course of Vegetative Growth and Flowering in Chenopodium rubrum.

The FT/TFL1 gene family controls important aspects of plant development: MFT-like genes affect germination, TFL1-like genes act as floral inhibitors, and FT-like genes are floral activators. Gene duplications produced paralogs with modified functions required by the specific lifestyles of various angiosperm species. We constructed the transcriptome of the weedy annual plant Chenopodium rubrum and used it for the comprehensive search for the FT/TFL1 genes. We analyzed their phylogenetic relationships across Amaranthaceae and all angiosperms. We discovered a very ancient phylogenetic clade of FT genes represented by the CrFTL3 gene of C. rubrum. Another paralog CrFTL2 showed an unusual structural rearrangement which might have contributed to the functional shift. We examined the transcription patterns of the FT/TFL1 genes during the vegetative growth and floral transition in C. rubrum to get clues about their possible functions. All the genes except for the constitutively expressed CrFTL2 gene, and the CrFTL3 gene, which was transcribed only in seeds, exhibited organ-specific expression influenced by the specific light regime. The CrFTL1 gene was confirmed as a single floral activator from the FT/TFL1 family in C. rubrum. Its floral promoting activity may be counteracted by CrTFL1. C. rubrum emerges as an easily manipulated model for the study of floral induction in weedy fast-cycling plants lacking a juvenile phase.

Revisiting the phosphatidylethanolamine‐binding protein (PEBP) gene family reveals cryptic FLOWERING LOCUS T gene homologs in gymnosperms and sheds new light on functional evolution

Angiosperms and gymnosperms are two major groups of extant seed plants. It has been suggested that gymnosperms lack FLOWERING LOCUS T (FT), a key integrator at the core of flowering pathways in angiosperms. Taking advantage of newly released gymnosperm genomes, we revisited the evolutionary history of the plant phosphatidylethanolamine-binding protein (PEBP) gene family through phylogenetic reconstruction. Expression patterns in three gymnosperm taxa and heterologous expression in Arabidopsis were studied to investigate the functions of gymnosperm FT-like and TERMINAL FLOWER 1 (TFL1)-like genes. Phylogenetic reconstruction suggests that an ancient gene duplication predating the divergence of seed plants gave rise to the FT and TFL1 genes. Expression patterns indicate that gymnosperm TFL1-like genes play a role in the reproductive development process, while GymFT1 and GymFT2, the FT-like genes resulting from a duplication event in the common ancestor of gymnosperms, function in both growth rhythm and sexual development pathways. When expressed in Arabidopsis, both spruce FT-like and TFL1-like genes repressed flowering. Our study demonstrates that gymnosperms do have FT-like and TFL1-like genes. Frequent gene and genome duplications contributed significantly to the expansion of the plant PEBP gene family. The expression patterns of gymnosperm PEBP genes provide novel insight into the functional evolution of this gene family.

Analysis of two TFL1 homologs of dogwood species (Cornus L.) indicates functional conservation in control of transition to flowering.

Two TFL1 -like genes, CorfloTFL1 and CorcanTFL1 cloned from Cornus florida and C. canadensis, function in regulating the transition to reproductive development in Arabidopsis. TERMINAL FLOWER 1 (TFL1) is known to regulate inflorescence development in Arabidopsis thaliana and to inhibit the transition from a vegetative to reproductive phase within the shoot apical meristem. Despite the importance, TFL1 homologs have been functionally characterized in only a handful eudicots. Here we report the role of TFL1 homologs of Cornus L. in asterid clade of eudicots. Two TFL1-like genes, CorfloTFL1 and CorcanTFL1, were cloned from Cornus florida (a tree) and C. canadensis (a subshrub), respectively. Both are deduced to encode proteins of 175 amino acids. The amino acid sequences of these two Cornus TFL1 homologs share a high similarity to Arabidopsis TFL1 and phylogenetically more close to TFL1 paralogous copy ATC (Arabidopsis thaliana CENTRORADIALIS homologue). Two genes are overexpressed in wild-type and tfl1 mutant plants of A. thaliana. The over-expression of each gene in wild-type Arabidopsis plants results in delaying flowering time, increase of plant height and cauline and rosette leaf numbers, excessive shoot buds, and secondary inflorescence branches. The over-expression of each gene in the tfl1 mutant rescued developmental defects, such as the early determinate inflorescence development, early flowering time, and other vegetative growth defects, to normal phenotypes of wild-type plants. These transgenic phenotypes are inherited in progenies. All data indicate that CorfloTFL1 and CorcanTFL1 have conserved the ancestral function of TFL1 and CEN regulating flowering time and inflorescence determinacy.

Promoting flowering, lateral shoot outgrowth, leaf development, and flower abscission in tobacco plants overexpressing cotton FLOWERING LOCUS T (FT)-like gene GhFT1.

FLOWERING LOCUS T (FT) encodes a mobile signal protein, recognized as major component of florigen, which has a central position in regulating flowering, and also plays important roles in various physiological aspects. A mode is recently emerging for the balance of indeterminate and determinate growth, which is controlled by the ratio of FT-like and TERMINAL FLOWER 1 (TFL1)-like gene activities, and has a strong influence on the floral transition and plant architecture. Orthologs of GhFT1 was previously isolated and characterized from Gossypium hirsutum. We demonstrated that ectopic overexpression of GhFT1 in tobacco, other than promoting flowering, promoted lateral shoot outgrowth at the base, induced more axillary bud at the axillae of rosette leaves, altered leaf morphology, increased chlorophyll content, had higher rate of photosynthesis and caused flowers abscission. Analysis of gene expression suggested that flower identity genes were significantly upregulated in transgenic plants. Further analysis of tobacco FT paralogs indicated that NtFT4, acting as flower inducer, was upregulated, whereas NtFT2 and NtFT3 as flower inhibitors were upregulated in transgenic plants under long-day conditions, but downregulated under short-day conditions. Our data suggests that sufficient level of transgenic cotton FT might disturb the balance of the endogenous tobacco FT paralogs of inducers and repressors and resulted in altered phenotype in transgenic tobacco, emphasizing the expanding roles of FT in regulating shoot architecture by advancing determine growth. Manipulating the ratio for indeterminate and determinate growth factors throughout FT-like and TFL1-like gene activity holds promise to improve plant architecture and enhance crop yield.

Environmental responses of the FT/TFL1 gene family and their involvement in flower induction in Fragaria × ananassa

Flowering time control is important for fruit production in Fragaria×ananassa. The flowering inhibition pathway has been extensively elucidated in the woodland strawberry, Fragaria vesca, whereas the factors involved in its promotion remain unclear. In this study, we investigated the environmental responses of F.×ananassa FT and TFL1-like genes, which are considered key floral promoters and repressors in many plants, respectively. A putative floral promoter, FaFT3, was up-regulated in the shoot tip under short-day and/or low growth temperature, in accordance with the result that these treatments promoted flowering. FaFT3 mRNA accumulated before induction of a floral meristem identity gene, FaAP1. FaFT2, a counterpart of FvFT2, expressed in the flower bud of F. vesca, was not induced in the shoot tip differentiating sepal or stamen, suggesting that this gene works at a later stage than stamen formation. In F. vesca, FvFT1 transmits the long-day signal perceived in the leaves to the shoot tip, and induces the potent floral inhibitor FvTFL1. FaFT1 was expressed in the leaves under long-day conditions in F.×ananassa. Expression of FaTFL1 was higher in the shoot tip under long-day than short-day conditions. Independent of day-length, FaTFL1 expression was higher under high temperature than low temperature conditions. These results suggest that FaFT3 induction by short-day or low temperature stimuli is a key step for flowering initiation. As in F. vesca, F.×ananassa floral inhibition pathways depend on FaTFL1 regulation by day-length via FaFT1, and by temperature.