Two flowering locus T (FT) homologs in Chenopodium rubrum differ in expression patterns

Leaf and shoot apical meristem transcriptomes of quinoa (Chenopodium quinoa Willd.) in response to photoperiod and plant development

Understanding the regulation of flowering time is crucial for adaptation of crops to new environment. In this study, we examined the timing of floral transition and analysed transcriptomes in leaf and shoot apical meristems of photoperiod-sensitive and -insensitive quinoa accessions. Histological analysis showed that floral transition in quinoa initiates 2-3 weeks after sowing. We found four groups of differentially expressed genes in quinoa genome that responded to plant development and floral transition: (i) 222 genes responsive to photoperiod in leaves, (ii) 1812 genes differentially expressed between accessions under long-day conditions in leaves, (iii) 57 genes responding to developmental changes under short-day conditions in leaves and (iv) 911 genes responding to floral transition within the shoot apical meristem. Interestingly, among numerous candidate genes, two putative FT orthologs together with other genes (e.g. SOC1, COL, AP1) were previously reported as key regulators of flowering time in other species. Additionally, we used coexpression networks to associate novel transcripts to a putative biological process based on the annotated genes within the same coexpression cluster. The candidate genes in this study would benefit quinoa breeding by identifying and integrating their beneficial haplotypes in crossing programs to develop adapted cultivars to diverse environmental conditions.

Ectopic expression of Jatropha curcas JcTAW1 improves the vegetative growth, yield, and drought resistance of tobacco

BACKGROUND

Jatropha curcas is a promising alternative bio-energy resource. However, underrun limited its broad application in the industry. Luckily, TAW1 is a high-productivity promoting gene that increases the lateral branches by prolonging the identification of inflorescence meristems to generate more spikes and flowers.

RESULTS

In the current study, we introduced the Jatropha JcTAW1 gene into tobacco to depict its functional profile. Ectopically expressed JcTAW1 increased the lateral branches and ultimate yield of the transgenic tobacco plants. Moreover, the JcTAW1 lines had significantly higher plant height, longer roots, and better drought resistance than those of wild-type (W.T.). We performed RNA sequencing and weighted gene co-expression network analysis to determine which biological processes were affected by JcTAW1. The results showed that biological processes such as carbon metabolism, cell wall biosynthesis, and ionization transport were extensively promoted by the ectopic expression of JcTAW1. Seven hub genes were identified. Therein, two up-regulated genes affect glucose metabolism and cell wall biosynthesis, five down-regulated genes are involved in DNA repair and negative regulation of TOR (target-of-rapamycin) signaling which was identified as a central regulator to promote cell proliferation and growth.

CONCLUSIONS

Our study verified a new promising candidate for Jatropha productive breeding and discovered several new features of JcTAW1. Except for boosting flowering, JcTAW1 was found to promote stem and root growth. Additionally, transcriptome analysis indicated that JcTAW1 might promote glucose metabolism while suppressing the DNA repair system.

Genome-wide identification and expression analysis disclose the pivotal PHOSPHATIDYLETHANOLAMINE BINDING PROTEIN members that may be utilized for yield improvement of Chenopodium quinoa

Quinoa (Chenopodium quinoa) is a prospective orphan crop that needs yield improvement. Previous studies indicate PHOSPHATIDYLETHANOLAMINE BINDING PROTEIN (PEBP) family genes are highly associated with the key agronomic traits of crops. Characterizing the pivotal PEBP genes will speed up the domestication and yield improvement of quinoa. Previous investigations on PEBP genes of Chenopodium species indicated that, the PEBP genes, despite in the same subclade, may have experienced functional diversification. Especially, the allotetraploidy (AABB) and numerous segmental duplications and chromosomal rearrangements in quinoa make it more difficult to understand the functions of PEBP genes. More recently, 6 quinoa FT subfamily genes were predicted to be related to flowering of quinoa. However, investigation on the whole PEBP family members is still lacking. In this study, we obtained 23 PEBP genes, including 5 MFT, 11 FTL and 7 TFL genes. We found 7 orthologous gene pairs, from sub-genome A and sub-genome B, respectively, showing collinearities with sugar beet. Evolution analysis on PEBP genes of two quinoa sub-genomes, sugar beet and relatives of diploid ancestors indicated that, the reasons for gene duplication events varied and 4 tandem duplications are the major reason for PEBP family expansion. Tissue-specific expression analysis suggested that expression patterns are mostly differing between orthologous gene pairs. Analysis on gene expressions at 6 stages suggested the possible positive roles of CqFTL1/CqFTL2, CqFTL5, CqFTL8, CqFTL6/CqFTL9 and CqTFL6/CqTFL7, and negative roles of CqTFL1/CqTFL2/CqTFL3, CqTFL4/CqTFL5 in inflorescence branching. Expression analysis in ABA-treated seed, in combination with the cis-acting element distribution analysis, indicated that CqMFT2, CqMFT3 and CqMFT4 may regulate seed germination via ABA signaling. Observations on responses to night break and photoperiod changes highlighted the roles of CqFTL5 and CqFTL8 under short day, and CqFTL6 under long day for quinoa flowering. Further, co-expression network analysis indicated that 64 transcription factors may act upstream of CqFTL5 and CqFTL8 to regulate flowering. Together, this study will help us identify the pivotal PEBP genes that may be utilized for quinoa breeding in future.

The Genetic and Hormonal Inducers of Continuous Flowering in Orchids: An Emerging View

Orchids are the flowers of magnetic beauty. Vivid and attractive flowers with magnificent shapes make them the king of the floriculture industry. However, the long-awaited flowering is a drawback to their market success, and therefore, flowering time regulation is the key to studies about orchid flower development. Although there are some rare orchids with a continuous flowering pattern, the molecular regulatory mechanisms are yet to be elucidated to find applicable solutions to other orchid species. Multiple regulatory pathways, such as photoperiod, vernalization, circadian clock, temperature and hormonal pathways are thought to signalize flower timing using a group of floral integrators. This mini review, thus, organizes the current knowledge of floral time regulators to suggest future perspectives on the continuous flowering mechanism that may help to plan functional studies to induce flowering revolution in precious orchid species.

Developing Chenopodium ficifolium as a potential B genome diploid model system for genetic characterization and improvement of allotetraploid quinoa (Chenopodium quinoa)

BACKGROUND

Quinoa (Chenopodium quinoa) is a high-value grain known for its excellent nutritional balance. It is an allotetraploid species (AABB, 2n = 4x = 36) formed by the hybridization between AA and BB genome diploid (2n = 2x = 18) species. This study reports genetic studies in Chenopodium ficifolium as a potential B genome diploid model system to simplify the genetic studies of quinoa including gene identification and marker-assisted breeding.

RESULTS

Portsmouth, New Hampshire and Quebec City, Quebec accessions of C. ficifolium were used to develop an F2 population segregating for agronomically relevant traits including flowering time, plant height, the number of branches, branch angle, and internode length. Marker-trait associations were identified for the FLOWERING LOCUS T-LIKE 1 (FTL1) marker gene, where the alternate alleles (A1/A2) were segregating among the F2 generation plants in association with flowering time, plant height, and the number of branches. There was a strong correlation of the flowering time trait with both plant height and the number of branches. Thus, a possible multifaceted functional role for FTL1 may be considered. The parental Portsmouth and Quebec City accessions were homozygous for the alternate FTL1 alleles, which were found to be substantially diverged. SNPs were identified in the FTL1 coding sequence that could have some functional significance in relation to the observed trait variation.

CONCLUSION

These results draw further attention to the possible functional roles of the FTL1 locus in Chenopodium and justify continued exploration of C. ficifolium as a potential diploid model system for the genetic study of quinoa. We expect our findings to aid in quinoa breeding as well as to any studies related to the Chenopodium genus.

Transcriptomic study of the night break in Chenopodium rubrum reveals possible upstream regulators of the floral activator CrFTL1

The transition from vegetative to reproductive phases is the most fundamental and tightly controlled switch in the life of flowering plants. The short-day plant Chenopodium rubrum is a fast cycling annual plant lacking a juvenile phase. It can be induced to flowering at the seedling stage by exposure to a single period of darkness. This floral induction may then be cancelled by a short pulse of red light at midnight called night break (NB), which also inhibits the floral activator FLOWERING LOCUS T LIKE 1 (CrFTL1). We performed a comparative transcriptomic study between C. rubrum seedlings treated by NB and ones growing through uninterrupted night, and found about six hundred differentially expressed genes, including the B-BOX DOMAIN (BBX) genes. We focused on the CrBBX19 and BOLTING TIME CONTROL 1 (BTC1) genes, homologous to the upstream regulators of the BvFT2, a floral inducer in sugar beet. The transcription patterns of the two genes were compatible with their putative role as a sensor of the dark period length optimal for flowering (CrBBX19), and a signal of lights-on (CrBTC1), but the participation of other genes cannot be excluded. The expression profiles of CrBBX19 and the homolog of the core endogenous clock gene LATE ELONGATED HYPOCOTYL (LHY) were highly similar, which suggested their co-regulation.

Haplotype variations of major flowering time genes in quinoa unveil their role in the adaptation to different environmental conditions

Response to photoperiod is of major importance in crop production. It defines the adaptation of plants to local environments. Quinoa is a short-day plant which had been domesticated in the Andeans regions. We wanted to understand the adaptation to long-day conditions by studying orthologues of two major flowering time regulators of Arabidopsis, FLOWERING LOCUS T (FT) and CONSTANS (CO) in quinoa accessions with contrasting photoperiod response. By searching the quinoa reference genome sequence, we identified 24 FT and six CO homologs. CqFT genes displayed remarkably different expression patterns between long- and short-day conditions, whereas the influence of the photoperiod on CqCOL expressions was moderate. Cultivation of 276 quinoa accessions under short- and long-day conditions revealed great differences in photoperiod sensitivity. After sequencing their genomes, we identified large sequence variations in 12 flowering time genes. We found non-random distribution of haplotypes across accessions from different geographical origins, highlighting the role of CqFT and CqCOL genes in the adaptation to different day-length conditions. We identified five haplotypes causing early flowering under long days. This study provides assets for quinoa breeding because superior haplotypes can be assembled in a predictive breeding approach to produce well-adapted early flowering lines under long-day photoperiods.

Identification of the specific long-noncoding RNAs involved in night-break mediated flowering retardation in Chenopodium quinoa

Background

Night-break (NB) has been proven to repress flowering of short-day plants (SDPs). Long-noncoding RNAs (lncRNAs) play key roles in plant flowering. However, investigation of the relationship between lncRNAs and NB responses is still limited, especially in Chenopodium quinoa, an important short-day coarse cereal.

Results

In this study, we performed strand-specific RNA-seq of leaf samples collected from quinoa seedlings treated by SD and NB. A total of 4914 high-confidence lncRNAs were identified, out of which 91 lncRNAs showed specific responses to SD and NB. Based on the expression profiles, we identified 17 positive- and 7 negative-flowering lncRNAs. Co-expression network analysis indicated that 1653 mRNAs were the common targets of both types of flowering lncRNAs. By mapping these targets to the known flowering pathways in model plants, we found some pivotal flowering homologs, including 2 florigen encoding genes (FT (FLOWERING LOCUS T) and TSF (TWIN SISTER of FT) homologs), 3 circadian clock related genes (EARLY FLOWERING 3 (ELF3), LATE ELONGATED HYPOCOTYL (LHY) and ELONGATED HYPOCOTYL 5 (HY5) homologs), 2 photoreceptor genes (PHYTOCHROME A (PHYA) and CRYPTOCHROME1 (CRY1) homologs), 1 B-BOX type CONSTANS (CO) homolog and 1 RELATED TO ABI3/VP1 (RAV1) homolog, were specifically affected by NB and competed by the positive and negative-flowering lncRNAs. We speculated that these potential flowering lncRNAs may mediate quinoa NB responses by modifying the expression of the floral homologous genes.

Conclusions

Together, the findings in this study will deepen our understanding of the roles of lncRNAs in NB responses, and provide valuable information for functional characterization in future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07605-2.

Analysis of the quinoa genome reveals conservation and divergence of the flowering pathways

Quinoa (Chenopodium quinoa Willd.) is a grain crop grown in the Andes renowned as a highly nutritious plant exhibiting tolerance to abiotic stress such as drought, cold and high salinity. Quinoa grows across a range of latitudes corresponding to differing day lengths, suggesting regional adaptations of flowering regulation. Improved understanding and subsequent modification of the flowering process, including flowering time, ensuring high yields, is one of the key factors behind expansion of cultivation zones and goals of the crop improvement programs worldwide. However, our understanding of the molecular basis of flower initiation and development in quinoa is limited. Here, we use a computational approach to perform genome-wide identification and analysis of 611 orthologues of the Arabidopsis thaliana flowering genes. Conservation of the genes belonging to the photoperiod, gibberellin and autonomous pathways was observed, while orthologues of the key genes found in the vernalisation pathway (FRI, FLC) were absent from the quinoa genome. Our analysis indicated that on average each Arabidopsis flowering gene has two orthologous copies in quinoa. Several genes including orthologues of MIF1, FT and TSF were identified as homologue-rich genes in quinoa. We also identified 459 quinoa-specific genes uniquely expressed in the flower and/or meristem, with no known orthologues in other species. The genes identified provide a resource and framework for further studies of flowering in quinoa and related species. It will serve as valuable resource for plant biologists, crop physiologists and breeders to facilitate further research and establishment of modern breeding programs for quinoa.

Chenopodium ficifolium flowers under long days without upregulation of FLOWERING LOCUS T (FT) homologs

Chenopodium ficifoliumflowered under long days despite much lower expression ofFLOWERING LOCUS Thomolog than under short days. Frequent duplications of the FLOWERING LOCUS T (FT) gene across various taxonomic lineages resulted in FT paralogs with floral repressor function, whereas others duplicates maintained their floral-promoting role. The FT gene has been confirmed as the inducer of photoperiodic flowering in most angiosperms analyzed to date. We identified all FT homologs in the transcriptome of Chenopodium ficifolium and in the genome of Chenopodium suecicum, which are closely related to diploid progenitors of the tetraploid crop Chenopodium quinoa, and estimated their expression during photoperiodic floral induction. We found that expression of FLOWERING LOCUS T like 1 (FTL1), the ortholog of the sugar beet floral activator BvFT2, correlated with floral induction in C. suecicum and short-day C. ficifolium, but not with floral induction in C. ficifolium with accelerated flowering under long days. This C. ficifolium accession was induced to flowering without the concomitant upregulation of any FT homolog.

RcAP1, a Homolog of APETALA1, is Associated with Flower Bud Differentiation and Floral Organ Morphogenesis in Rosa chinensis

Rosa chinensis is one of the most popular flower plants worldwide. The recurrent flowering trait greatly enhances the ornamental value of roses, and is the result of the constant formation of new flower buds. Flower bud differentiation has always been a major topic of interest among researchers. The APETALA1 (AP1) MADS-box (Mcm1, Agamous, Deficiens and SRF) transcription factor-encoding gene is important for the formation of the floral meristem and floral organs. However, research on the rose AP1 gene has been limited. Thus, we isolated AP1 from Rosa chinensis ‘Old Blush’. An expression analysis revealed that RcAP1 was not expressed before the floral primordia formation stage in flower buds. The overexpression of RcAP1 in Arabidopsis thaliana resulted in an early-flowering phenotype. Additionally, the virus-induced down-regulation of RcAP1 expression delayed flowering in ‘Old Blush’. Moreover, RcAP1 was specifically expressed in the sepals of floral organs, while its expression was down-regulated in abnormal sepals and leaf-like organs. These observations suggest that RcAP1 may contribute to rose bud differentiation as well as floral organ morphogenesis, especially the sepals. These results may help for further characterization of the regulatory mechanisms of the recurrent flowering trait in rose.

Natural variation in Brassica FT homeologs influences multiple agronomic traits including flowering time, silique shape, oil profile, stomatal morphology and plant height in B. juncea

Natural structural variants of regulatory proteins causing quantitative phenotypic consequences have not been reported in plants. Herein, we show that 28 natural structural variants of FT homeologs, isolated from 6 species of Brassica, differ with respect to amino-acid substitutions in regions critical for interactions with FD and represent two evolutionarily distinct categories. Analysis of structural models of selected candidates from Brassica juncea (BjuFT_AAMF1) and Brassica napus (BnaFT_CCLF) predicted stronger binding between BjuFT and Arabidopsis thaliana FD. Over-expression of BjuFT and BnaFT in wild type and ft-10 mutant backgrounds of Arabidopsis validated higher potency of BjuFT in triggering floral transition. Analysis of gain-of-function and artificial miRNA mediated silenced lines of B. juncea implicated Brassica FT in multiple agronomic traits beyond flowering, consistent with a pleiotropic effect. Several dependent and independent traits such as lateral branching, silique shape, seed size, oil-profile, stomatal morphology and plant height were found altered in mutant lines. Enhanced FT levels caused early flowering, which in turn was positively correlated to a higher proportion of desirable fatty acids (PUFA). However, higher FT levels also resulted in altered silique shape and reduced seed size, suggesting trait trade-offs. Modulation of FT levels for achieving optimal balance of trait values and parsing pair-wise interactions among a reportoire of regulatory protein homeologs in polyploid genomes are indeed future areas of crop research.

Hybridization and polyploidization within the Chenopodium album aggregate analysed by means of cytological and molecular markers

Hybridization and polyploidization represent an important speciation mechanism in the diploid-polyploid complex of the Chenopodium album aggregate. In the present study we successfully reconstructed the evolutionary histories of the majority of Eurasian representatives of the C. album aggregate, resulting in the most comprehensive phylogenetic analysis of this taxonomically intricate group of species to date. We applied a combination of classical karyology for precise chromosome number determination, genomic in-situ hybridization for the determination of genomic composition, flow cytometry for the estimation of genome size and sequencing of plastid (cpDNA) and nuclear (ribosomal internal transcribed spacer - ITS and the introns of the FLOWERING LOCUS T LIKE genes - FTL) markers for a phylogenetic reconstruction and the identification of parental genomes in polyploid taxa. The FTL markers identified eight well supported evolutionary lineages. Five of them include at least one diploid species, and the remaining three comprise solely the subgenomes of polyploids that probably represent extinct or unknown diploid taxa. The existence of eight basic diploid lineages explains the origin of seven Eurasian polyploid groups and brings evidence of a nearly unlimited number of subgenomic combinations. The supposed promiscuity generated new species wherever different diploid lineages met each other and gave rise to tetraploid species or whenever they met other tetraploid species to produce hexaploid species throughout their evolutionary history. Finally, we unravelled a surprisingly simple scheme of polyploid species formation within the C. album aggregate. We determined seven groups of polyploid species differing in their origin in either Eurasia or Africa and convincingly demonstrated that (1) all Chenopodium polyploid species under study are of allopolyploid origin, (2) there are eight major monophyletic evolutionary lineages represented by extant or extinct/unknown diploid taxa, (3) those monophyletic lineages represent individual subgenomes, (4) hybridization among the lineages created seven subgenomic combinations of polyploid taxa, (5) taxa represented by particular subgenome combinations were further subjected to diversification, and (6) the majority of species are relatively young, not exceeding the age of the Quaternary period.

Evaluation of reference genes for reverse transcription quantitative real-time PCR (RT-qPCR) studies in Silene vulgaris considering the method of cDNA preparation

Accurate gene expression measurements are essential in studies of both crop and wild plants. Reverse transcription quantitative real-time PCR (RT-qPCR) has become a preferred tool for gene expression estimation. A selection of suitable reference genes for the normalization of transcript levels is an essential prerequisite of accurate RT-qPCR results. We evaluated the expression stability of eight candidate reference genes across roots, leaves, flower buds and pollen of Silene vulgaris (bladder campion), a model plant for the study of gynodioecy. As random priming of cDNA is recommended for the study of organellar transcripts and poly(A) selection is indicated for nuclear transcripts, we estimated gene expression with both random-primed and oligo(dT)-primed cDNA. Accordingly, we determined reference genes that perform well with oligo(dT)- and random-primed cDNA, making it possible to estimate levels of nucleus-derived transcripts in the same cDNA samples as used for organellar transcripts, a key benefit in studies of cyto-nuclear interactions. Gene expression variance was estimated by RefFinder, which integrates four different analytical tools. The SvACT and SvGAPDH genes were the most stable candidates across various organs of S. vulgaris, regardless of whether pollen was included or not.

The genome of Chenopodium quinoa

Chenopodium quinoa (quinoa) is a highly nutritious grain identified as an important crop to improve world food security. Unfortunately, few resources are available to facilitate its genetic improvement. Here we report the assembly of a high-quality, chromosome-scale reference genome sequence for quinoa, which was produced using single-molecule real-time sequencing in combination with optical, chromosome-contact and genetic maps. We also report the sequencing of two diploids from the ancestral gene pools of quinoa, which enables the identification of sub-genomes in quinoa, and reduced-coverage genome sequences for 22 other samples of the allotetraploid goosefoot complex. The genome sequence facilitated the identification of the transcription factor likely to control the production of anti-nutritional triterpenoid saponins found in quinoa seeds, including a mutation that appears to cause alternative splicing and a premature stop codon in sweet quinoa strains. These genomic resources are an important first step towards the genetic improvement of quinoa.

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.

A dark-light transition triggers expression of the floral promoter CrFTL1 and downregulates CONSTANS-like genes in a short-day plant Chenopodium rubrum

The proper timing of flowering is essential for the adaptation of plant species to their ever-changing environments. The central position in a complex regulatory network is occupied by the protein FT, which acts as a florigen. We found that light, following a permissive period of darkness, was essential to induce the floral promoter CrFTL1 and to initiate flowering in seedlings of the short-day plant Chenopodium rubrum L. We also identified two novel CONSTANS-like genes in C. rubrum and observed their rhythmic diurnal and circadian expressions. Strong rhythmicity of expression suggested that the two genes might have been involved in the regulation of photoperiod-dependent processes, despite their inability to complement co mutation in A. thaliana. The CrCOL1 and CrCOL2 genes were downregulated by dark-light transition, regardless of the length of a preceding dark period. The same treatment activated the floral promoter CrFTL1. Light therefore affected CrCOL and CrFTL1 in an opposite manner. Both CrCOL genes and CrFTL1 displayed expression patterns unique among short-day plants. Chenopodium rubrum, the subject of classical physiological studies in the past, is emerging as a useful model for the investigation of flowering at the molecular level.

Photoperiodic control of FT-like gene ClFT initiates flowering in Chrysanthemum lavandulifolium

The FLOWERING LOCUS T (FT) gene plays crucial roles in regulating the transition from the vegetative phase to the reproductive phase. In this study, we isolated an FT homologous gene (denoted as ClFT) from Chrysanthemum lavandulifolium. The sequencing analysis indicated that the promoter of the ClFT gene contains many elements, such as light response, abscisic acid, drought-inducibility response and CIRCADIAN clock elements. The expression patterns of ClFT in different tissues/organs at different developmental stages and its responses to different photoperiods were observed. ClFT is expressed in all tested organs/tissues, with the highest expression level being observed in the leaves of plants with visible floral buds under the short day (SD) condition. Next, we studied the rhythmic expression of ClFT during different photoperiod treatments and found that the level of ClFT increases with additional hours of continuous dark. ClFT accumulates when the continuous dark period is 12 h, regardless of the duration of light period. The ectopic expression of the ClFT gene in wild type Arabidopsis (Col-0) results in early flowering, with high expression levels of endogenous LFY and SOC1 being observed in transgenic Arabidopsis. All results indicated that the ClFT gene plays an evolutionarily conserved role in promoting flowering in inductive short days in C. lavandulifolium and that this gene could serve as a vital target for the genetic manipulation of flowering time in chrysanthemums.

Overexpression of the auxin binding protein1 modulates PIN-dependent auxin transport in tobacco cells

BACKGROUND

Auxin binding protein 1 (ABP1) is a putative auxin receptor and its function is indispensable for plant growth and development. ABP1 has been shown to be involved in auxin-dependent regulation of cell division and expansion, in plasma-membrane-related processes such as changes in transmembrane potential, and in the regulation of clathrin-dependent endocytosis. However, the ABP1-regulated downstream pathway remains elusive.

METHODOLOGY/PRINCIPAL FINDINGS

Using auxin transport assays and quantitative analysis of cellular morphology we show that ABP1 regulates auxin efflux from tobacco BY-2 cells. The overexpression of ABP1can counterbalance increased auxin efflux and auxin starvation phenotypes caused by the overexpression of PIN auxin efflux carrier. Relevant mechanism involves the ABP1-controlled vesicle trafficking processes, including positive regulation of endocytosis of PIN auxin efflux carriers, as indicated by fluorescence recovery after photobleaching (FRAP) and pharmacological manipulations.

CONCLUSIONS/SIGNIFICANCE

The findings indicate the involvement of ABP1 in control of rate of auxin transport across plasma membrane emphasizing the role of ABP1 in regulation of PIN activity at the plasma membrane, and highlighting the relevance of ABP1 for the formation of developmentally important, PIN-dependent auxin gradients.

Proteins from the FLOWERING LOCUS T-like subclade of the PEBP family act antagonistically to regulate floral initiation in tobacco

Flowering is an important agronomic trait that often depends on the integration of photoperiod, vernalization, gibberellin and/or autonomous signaling pathways by regulatory proteins such as FLOWERING LOCUS T (FT), a member of the phosphatidylethanolamine-binding protein (PEBP) family. Six PEBP family proteins control flowering in the model plant Arabidopsis thaliana, and their regulatory functions are well established, but variation in the number and structural diversity of PEBPs in different species means their precise functions must be determined on a case-by-case basis. We isolated four novel FT-like genes from Nicotiana tabacum (tobacco), and determined their expression profiles in wild-type plants and their overexpression phenotypes in transgenic plants. We found that all four genes were expressed in leaves under short-day conditions, and at least NtFT3 expression was restricted to phloem companion cells. We also found that the NtFT1, NtFT2 and NtFT3 proteins are floral inhibitors (atypical for FT-like proteins), whereas only NtFT4 is a floral inducer. We were unable to detect the expression of these genes under long-day conditions, suggesting that all four tobacco FT-like proteins may control flowering in response to short days. Phylogenetic analysis of PEBP family proteins and their functions in different solanaceous species confirmed that gene duplication and divergence within the FT-like clade has led to the evolution of antagonistic regulators that may help to fine-tune floral initiation in response to environmental cues.

Recent advances of flowering locus T gene in higher plants

Flowering Locus T (FT) can promote flowering in the plant photoperiod pathway and also facilitates vernalization flowering pathways and other ways to promote flowering. The expression of products of the FT gene is recognized as important parts of the flowering hormone and can induce flowering by long-distance transportation. In the present study, many FT-like genes were isolated, and the transgenic results show that FT gene can promote flowering in plants. This paper reviews the progress of the FT gene and its expression products to provide meaningful information for further studies of the functions of FT genes.

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.

The Medicago FLOWERING LOCUS T homolog, MtFTa1, is a key regulator of flowering time

FLOWERING LOCUS T (FT) genes encode proteins that function as the mobile floral signal, florigen. In this study, we characterized five FT-like genes from the model legume, Medicago (Medicago truncatula). The different FT genes showed distinct patterns of expression and responses to environmental cues. Three of the FT genes (MtFTa1, MtFTb1, and MtFTc) were able to complement the Arabidopsis (Arabidopsis thaliana) ft-1 mutant, suggesting that they are capable of functioning as florigen. MtFTa1 is the only one of the FT genes that is up-regulated by both long days (LDs) and vernalization, conditions that promote Medicago flowering, and transgenic Medicago plants overexpressing the MtFTa1 gene flowered very rapidly. The key role MtFTa1 plays in regulating flowering was demonstrated by the identification of fta1 mutants that flowered significantly later in all conditions examined. fta1 mutants do not respond to vernalization but are still responsive to LDs, indicating that the induction of flowering by prolonged cold acts solely through MtFTa1, whereas photoperiodic induction of flowering involves other genes, possibly MtFTb1, which is only expressed in leaves under LD conditions and therefore might contribute to the photoperiodic regulation of flowering. The role of the MtFTc gene is unclear, as the ftc mutants did not have any obvious flowering-time or other phenotypes. Overall, this work reveals the diversity of the regulation and function of the Medicago FT family.

The FT-like ZCN8 Gene Functions as a Floral Activator and Is Involved in Photoperiod Sensitivity in Maize

The mobile floral-promoting signal, florigen, is thought to consist of, in part, the FT protein named after the Arabidopsis thaliana gene FLOWERING LOCUS T. FT is transcribed and translated in leaves and its protein moves via the phloem to the shoot apical meristem where it promotes the transition from vegetative to reproductive development. In our search for a maize FT-like floral activator(s), seven Zea mays CENTRORADIALIS (ZCN) genes encoding FT homologous proteins were studied. ZCN8 stood out as the only ZCN having the requisite characteristics for possessing florigenic activity. In photoperiod sensitive tropical lines, ZCN8 transcripts were strongly upregulated in a diurnal manner under floral-inductive short days. In day-neutral temperate lines, ZCN8 mRNA level was independent of daylength and displayed only a weak cycling pattern. ZCN8 is normally expressed in leaf phloem, but ectopic expression of ZCN8 in vegetative stage shoot apices induced early flowering in transgenic plants. Silencing of ZCN8 by artificial microRNA resulted in late flowering. ZCN8 was placed downstream of indeterminate1 and upstream of delayed flowering1, two other floral activator genes. We propose a flowering model linking photoperiod sensitivity of tropical maize to diurnal regulation of ZCN8.

Two coordinately regulated homologs of FLOWERING LOCUS T are involved in the control of photoperiodic flowering in soybean

FLOWERING LOCUS T (FT) is a key flowering integrator in Arabidopsis (Arabidopsis thaliana), with homologs that encode florigens in many plant species regardless of the type of photoperiodic response. We identified 10 FT homologs, which were arranged as five pairs of linked genes in different homoeologous chromosomal regions, in soybean (Glycine max), a paleopolyploid species. Two of the FT homologs, GmFT2a and GmFT5a, were highly up-regulated under short-day (SD) conditions (inductive for flowering in soybean) and had diurnal expression patterns with the highest expression 4 h after dawn. Under long-day (LD) conditions, expression of GmFT2a and GmFT5a was down-regulated and did not follow a diurnal pattern. Flowering took much longer to initiate under LD than under SD, and only the GmFT5a transcript accumulated late in development under LD. Ectopic expression analysis in Arabidopsis confirmed that both GmFT2a and GmFT5a had the same function as Arabidopsis FT, but the effect of GmFT5a was more prominent. A double-mutant soybean line for two PHYTOCHROME A (PHYA) genes expressed high levels of GmFT2a and GmFT5a under LD, and it flowered slightly earlier under LD than the wild type grown under SD. The expression levels of GmFT2a and GmFT5a were regulated by the PHYA-mediated photoperiodic regulation system, and the GmFT5a expression was also regulated by a photoperiod-independent system in LD. Taken together, our results suggest that GmFT2a and GmFT5a coordinately control flowering and enable the adaptation of soybean to a wide range of photoperiodic environments.