Early evolution of the MFT-like gene family in plants

Angiosperm genes sharing a conserved phosphatidylethanolamine-binding (PEPB) domain have been shown to be involved in the control of shoot meristem identity and flowering time. The family is divided into three subfamilies, FT-like, TFL1-like and MFT-like. This study is focused on the evolution of the MFT-like clade, suggested to be ancestral to the two other clades. We report that the bryophyte Physcomitrella patens and the lycopod Selaginella moellendorfii contain four and two MFT-like genes respectively. Neither species have any FT or TFL1-like genes. Furthermore, we have identified a new subclade of MFT-like genes in Angiosperms. Quantitative expression analysis of MFT-like genes in Physcomitrella patens reveals that the expression patterns are circadian and reaches maximum in gametangia and sporophytes. Our data suggest that the occurrence FT and TFL1-like genes, is associated with the evolution of seed plants. Expression data for Physcomitrella MFT-like genes implicates an involvement in the development of reproductive tissues in the moss.     

A complementary role for ELF3 and TFL1 in the regulation of flowering time by ambient temperature

Plants regulate their time to flowering by gathering information from the environment. Photoperiod and temperature are among the most important environmental variables. Sub-optimal, but not near-freezing, temperatures regulate flowering through the thermosensory pathway, which overlaps with the autonomous pathway. Here we show that ambient temperature regulates flowering by two genetically distinguishable pathways, one requiring TFL1 and another requiring ELF3 . The delay in flowering time observed at lower temperatures was partially suppressed in single elf3 and tfl1 mutants, whereas double elf3 tfl1 mutants were insensitive to temperature. tfl1 mutations abolished the temperature response in cryptochrome mutants that are deficient in photoperiod perception, but not in phyB mutants, which have a constitutive photoperiodic response. In contrast to tfl1 , elf3 mutations were able to suppress the temperature response in phyB mutants, but not in cryptochrome mutants. Gene expression profiles revealed that the tfl1 and elf3 effects are due to the activation of different sets of genes, and identified CCA1 and SOC1/AGL20 as being important cross-talk points. Finally, genome-wide gene expression analysis strongly suggests a general and complementary role for ELF3 and TFL1 in temperature signalling.     

小麦CEN/TFL1-like cDNA克隆及其编码序列分析

以水稻、金鱼草、拟南芥CEN/TFL1蛋白质序列为参考,以小麦中CEN/TFL1基因同源EST片段为依据设计特异引物,利用RT-PCR从普通小麦‘中国春’幼穗总RNA中扩增出549 bp的特异片段。测序结果表明,该片段包含了完整的ORF,编码产物为典型的CEN/TFL1-like蛋白家族成员。序列比对表明,该基因编码产物与黑麦草LpTFL1、水稻FDR2和FDR1以及玉米ZmTFL1亲缘关系最近,分别具有96.5%、96.0%、93.6%和95.4%的相似性;与哺乳动物Rattus norveqicus磷脂酰乙醇胺结合蛋白(PEBP)具有38.9%相似性。空间结构预测表明,该蛋白具有PEBP家族成员的典型三维结构。     

PPF1 may suppress plant senescence via activating TFL1 in transgenic Arabidopsis plants

Senescence, a sequence of biochemical and physiological events, constitutes the final stage of development In higher plants and is modulated by a variety of environmental factors and intemal factors. PPF1 possesses an important biological function in plant development by controlling the Ca2 storage capacity within chloroplasts. Here we show that the expression of PPF1 might play a pivotal role in negatively regulating plant senescence as revealed by the regulation of overexpression and suppression of PPF1 on plant development. Moreover, TFL1, a key regulator in the floral repression pathway, was screened out as one of the downstream targets for PPF1 in the senescence-signaling pathway. Investigation of the senescence-related phenotypes in PPF1(-) tfl1-1 and PPF1( ) tfl1-1 double mutants confirmed and further highlighted the relation of PPF1 with TFL1 in tranegenic plants. The activation of TFL1 expression by PPF1 defines an important pathway possibly essential for the negative regulation of plant senescence in transgenic Arabidopsis.     

Characterization of the Arabidopsis TU8 Glucosinolate Mutation,an Allele of TERMINAL FLOWER2

Glucosinolates are a group of defense-related secondary metabolites found in Arabidopsis and other cruciferous plants. Levels of leaf glucosinolates are regulated during plant development and increase in response to mechanical damage or insect feeding. The Arabidopsis TU8 mutant has a developmentally altered leaf glucosinolate profile: aliphatic glucosinolate levels drop off more rapidly, consistent with the early senescence of the mutant, and the levels of two indole glucosinolates are uniformly low. In TU8 seeds, four long-chain aliphatic glucosinolates have significantly increased levels, whereas the indolyl-3-methyl glucosinolate level is significantly reduced relative to wild type. Genetic mapping and DNA sequencing identified the TU8 mutation as tfl2-6, a new allele of TERMINAL FLOWER2 (TFL2), the only Arabidopsis homolog of animal HETEROCHROMATIN PROTEIN1 (HP1). TU8 (tfl2-6) has other previously identified tfl2 phenotypes, including an early transition to flowering, altered meristem structure, and stunted leaves. Analysis of two additional alleles, tfl2-1 and tfl2-2, showed glucosinolate profiles similar to those of line TU8 (tfl2-6).     

Fruit load modulates flowering-related gene expression in buds of alternate-bearing ‘Moncada’ mandarin

Background and Aims

Gene determination of flowering is the result of complex interactions involving both promoters and inhibitors. In this study, the expression of flowering-related genes at the meristem level in alternate-bearing citrus trees is analysed, together with the interplay between buds and leaves in the determination of flowering.

Methods

First defruiting experiments were performed to manipulate blossoming intensity in ‘Moncada’ mandarin, Citrus clementina. Further defoliation was performed to elucidate the role leaves play in the flowering process. In both cases, the activity of flowering-related genes was investigated at the flower induction (November) and differentiation (February) stages.

Key Results

Study of the expression pattern of flowering-genes in buds from on (fully loaded) and off (without fruits) trees revealed that homologues of FLOWERING LOCUS T (CiFT), TWIN SISTER OF FT (TSF), APETALA1 (CsAP1) and LEAFY (CsLFY) were negatively affected by fruit load. CiFT and TSF activities showed a marked increase in buds from off trees through the study period (ten-fold in November). By contrast, expression of the homologues of the flowering inhibitors of TERMINAL FLOWER 1 (CsTFL), TERMINAL FLOWER 2 (TFL2) and FLOWERING LOCUS C (FLC) was generally lower in off trees. Regarding floral identity genes, the increase in CsAP1 expression in off trees was much greater in buds than in leaves, and significant variations in CsLFY expression (approx. 20 %) were found only in February. Defoliation experiments further revealed that the absence of leaves completely abolished blossoming and severely affected the expression of most of the flowering-related genes, particularly decreasing the activity of floral promoters and of CsAP1 at the induction stage.

Conclusions

These results suggest that the presence of fruit affects flowering by greatly altering gene-expression not only at the leaf but also at the meristem level. Although leaves are required for flowering to occur, their absence strongly affects the activity of floral promoters and identity genes.     

The <Emphasis Type="Italic">FT/TFL1</Emphasis> gene family in grapevine

The FT/TFL1 gene family encodes proteins with similarity to phosphatidylethanolamine binding proteins which function as flowering promoters and repressors. We show here that the FT/TFL1 gene family in Vitis vinifera is composed of at least five genes. Sequence comparisons with homologous genes identified in other dicot species group them in three major clades, the FT, MFT and TFL1 subfamilies, the latter including three of the Vitis sequences. Gene expression patterns are in agreement with a role of VvFT and VvMFT as flowering promoters; while VvTFL1A, VvTFL1B and VvTFL1C could be associated with vegetative development and maintenance of meristem indetermination. Overexpression of VvFT in transgenic Arabidopsis plants generates early flowering phenotypes similar to those produced by FT supporting a role for this gene in flowering promotion. Overexpression of VvTFL1A does not affect flowering time but the determination of flower meristems, strongly altering inflorescence structure, which is consistent with the biological roles assigned to similar genes in other species.     

Fruit regulates seasonal expression of flowering genes in alternate-bearing 'Moncada' mandarin

Background and Aims

The presence of fruit has been widely reported to act as an inhibitor of flowering in fruit trees. This study is an investigation into the effect of fruit load on flowering of ‘Moncada’ mandarin and on the expression of putative orthologues of genes involved in flowering pathways to provide insight into the molecular mechanisms underlying alternate bearing in citrus.

Methods

The relationship between fruit load and flowering intensity was examined first. Defruiting experiments were further conducted to demonstrate the causal effect of fruit removal upon flowering. Finally, the activity of flowering-related genes was investigated to determine the extent to which their seasonal expression is affected by fruit yield.

Key Results

First observations and defruiting experiments indicated a significant inverse relationship between preceding fruit load and flowering intensity. Moreover, data indicated that when fruit remained on the tree from November onwards, a dramatic inhibition of flowering occurred the following spring. The study of the expression pattern of flowering-genes of on (fully loaded) and off (without fruits) trees revealed that homologues of FLOWERING LOCUS T (FT), SUPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1), APETALA1 (AP1) and LEAFY (LFY) were negatively affected by fruit load. Thus, CiFT expression showed a progressive increase in leaves from off trees through the study period, the highest differences found from December onwards (10-fold). Whereas differences in the relative expression of SOC1 only reached significance from September to mid-December, CsAP1 expression was constantly higher in those trees through the whole study period. Significant variations in CsLFY expression only were found in late February (close to 20 %). On the other hand, the expression of the homologues of TERMINAL FLOWER 1 (TFL1) and FLOWERING LOCUS C (FLC) did not appear to be related to fruit load.

Conclusions

These results suggest for the first time that fruit inhibits flowering by repressing CiFT and SOC1 expression in leaves of alternate-bearing citrus. Fruit also reduces CsAP1 expression in leaves, and the significant increase in leaf CsLFY expression from off trees in late February was associated with the onset of floral differentiation.     

Genetic interactions reveal the antagonistic roles of FT/TSF and TFL1 in the determination of inflorescence meristem identity in Arabidopsis

During the transition to the reproductive phase, the shoot apical meristem switches from the developmental program that generates vegetative organs to instead produce flowers. In this study, we examined the genetic interactions of FLOWERING LOCUS T (FT)/TWIN SISTER OF FT (TSF) and TERMINAL FLOWER 1 (TFL1) in the determination of inflorescence meristem identity in Arabidopsis thaliana. The ft‐10 tsf‐1 mutants produced a compact inflorescence surrounded by serrated leaves (hyper‐vegetative shoot) at the early bolting stage, as did plants overexpressing TFL1. Plants overexpressing FT or TSF (or both FT and TFL1) generated a terminal flower, as did tfl1‐20 mutants. The terminal flower formed in tfl1‐20 mutants converted to a hyper‐vegetative shoot in ft‐10 tsf‐1 mutants. Grafting ft‐10 tsf‐1 or ft‐10 tsf‐1 tfl1‐20 mutant scions to 35S::FT rootstock plants produced a normal inflorescence and a terminal flower in the scion plants, respectively, although both scions showed similar early flowering. Misexpression of FT in the vasculature and in the shoot apex in wild‐type plants generated a normal inflorescence and a terminal flower, respectively. By contrast, in ft‐10 tsf‐1 mutants the vasculature‐specific misexpression of FT converted the hyper‐vegetative shoot to a normal inflorescence, and in the ft‐10 tsf‐1 tfl1‐20 mutants converted the shoot to a terminal flower. TFL1 levels did not affect the inflorescence morphology caused by FT/TSF overexpression at the early bolting stage. Taking these results together, we proposed that FT/TSF and TFL1 play antagonistic roles in the determination of inflorescence meristem identity, and that FT/TSF are more important than TFL1 in this process.     

Altering FVE/MSI4 results in a substantial increase of biomass in Arabidopsis—the functional analysis of an ontogenesis accelerator

FVE/MSI4, a highly conserved gene through evolution, is considered a classical flowering time gene from the autonomous pathway in Arabidopsis thaliana. Our work provides complementary, yet distinct, evidence that mutations in FVE/MSI4 have highly pleiotropic effects on plant architecture and organ production and growth, indicating an overall role in reprogramming the genome. First, this is illustrated by the fact that fve mutants and transgenic versions of the gene show no morphological aberrations while living, on average, twice as long and producing more biomass and seeds than the wild type. For example, depending on the photoperiod, the vegetative biomass in the mutants is increased three- to eightfold. FVE/MSI4 can therefore be considered a multifactor component of biomass and yield. Second, the gene functions primarily at the shoot apical meristem, acting to calibrate its overall cell proliferation activity and organ initiation. At the same time, FVE/MSI4 regulates cell growth during organ formation mainly by modulating the timing of proliferation—differentiation transition and that of endoreduplication. FVE/MSI4 is an accelerator of ontogenesis. The function of the gene is to scale-down meristem activities, while accelerating developmental transitions and cellular differentiation. Genes of the kind are ideal tools in biotech for engineering biomass and yield according to geographical or climate constraints. The results enhance our understanding on the role epigenetic components of the genome, such as FVE/MSI4, play in adaptation and biomass calibration. They also illustrate the kind of functional characterization biotech applications might require during the first steps of product development. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.