The regulation of seasonal flowering in the Rosaceae

Genome Identification of B-BOX Gene Family Members in Seven Rosaceae Species and Their Expression Analysis in Response to Flower Induction in Malus domestica

BBX proteins play important roles in regulating plant growth and development including photomorphogenesis, photoperiodic regulation of flowering, and responses to biotic and abiotic stresses. At present, the genomes of seven Rosaceae fruit species have been fully sequenced. However, little is known about the BBX gene family and their evolutionary history in these Rosaceae species. Therefore, in this study total, 212 BBX genes were investigated from seven Rosaceae species (67 from Malus × domestica, 40 from Pyruscommunis, 22 from Rosa Chinesis, 20 from Prunuspersica, 21 from Fragariavesca, 22 from Prunusavium, and 20 from Rubusoccidentalis). The chemical properties, gene structures, and evolutionary relationships of the BBX genes were also studied. All the BBX genes were grouped into six subfamilies on the basis of their phylogenetic relationships and structural features. Analysis of gene structure, segmental and tandem duplication, gene phylogeny, and tissue-specific expression with the ArrayExpress database showed their diversification in function, quantity, and structure. The expression profiles of 19 MdBBX genes in different tissues were evaluated through qRT-PCR. These genes showed distinct transcription level among the tested tissues (bud, flower, fruit, stem, and leaf). Moreover, expression patterns of 19 MdBBX genes were examined during flowering induction time under flowering-related hormones and treatments (GA3, 6-BA, and sucrose). The expressions of the candidates BBX genes were affected and showed diverse expression profile. Furthermore, changes in response to these flowering-related hormones and treatment specifying their potential involvement in flowering induction. Based on these findings, BBX genes could be used as potential genetic markers for the growth and development of plants particularly in the area of functional analysis, and their involvement in flower induction in fruit plants.

Dormant Flower Buds Actively Accumulate Starch over Winter in Sweet Cherry

Temperate woody perennials survive to low temperatures in winter entering a dormant stage. Dormancy is not just a survival strategy, since chilling accumulation is required for proper flowering and arbitrates species adaptation to different latitudes. In spite of the fact that chilling requirements have been known for two centuries, the biological basis behind remain elusive. Since chilling accumulation is required for the normal growth of flower buds, it is tempting to hypothesize that something might be going on at this particular stage during winter dormancy. Here, we characterized flower bud development in relation to dormancy, quantifying changes in starch in the flower primordia in two sweet cherry cultivars over a cold and a mild year. Results show that, along the winter, flower buds remain at the same phenological stage with flower primordia at the very same developmental stage. But, surprisingly, important variation in the starch content of the ovary primordia cells occurs. Starch accumulated following the same pattern than chilling accumulation and reaching a maximum at chilling fulfillment. This starch subsequently vanished during ecodormancy concomitantly with ovary development before budbreak. These results showed that, along the apparent inactivity during endodormancy, flower primordia were physiologically active accumulating starch, providing a biological basis to understand chilling requirements.

Modulation of Dormancy and Growth Responses in Reproductive Buds of Temperate Trees

During autumn perennial trees cease growth and form structures called buds in order to protect meristems from the unfavorable environmental conditions, including low temperature and desiccation. In addition to increased tolerance to these abiotic stresses, reproductive buds modulate developmental programs leading to dormancy induction to avoid premature growth resumption, and flowering pathways. Stress tolerance, dormancy, and flowering processes are thus physically and temporarily restricted to a bud, and consequently forced to interact at the regulatory level. We review recent genomic, genetic, and molecular contributions to the knowledge of these three processes in trees, highlighting the role of epigenetic modifications, phytohormones, and common regulatory factors. Finally, we emphasize the utility of transcriptomic approaches for the identification of key structural and regulatory genes involved in bud processes, illustrated with our own experience using peach as a model.

Altered regulation of TERMINAL FLOWER 1 causes the unique vernalisation response in an arctic woodland strawberry accession

Vernalisation requirement is an agriculturally important trait that postpones the development of cold-sensitive floral organs until the spring. The family Rosaceae includes many agriculturally important fruit and berry crops that suffer from crop losses caused by frost injury to overwintering flower buds. Recently, a vernalisation-requiring accession of the Rosaceae model woodland strawberry (Fragaria vesca) has been identified in northern Norway. Understanding the molecular basis of the vernalisation requirement in this accession would advance the development of strawberry cultivars better adapted to temperate climate. We use gene silencing, gene expression analysis, genetic mapping and population genomics to study the genetic basis of the vernalisation requirement in woodland strawberry. Our results indicate that the woodland strawberry vernalisation requirement is endemic to northern Norwegian population, and mapping data suggest the orthologue of TERMINAL FLOWER1 (FvTFL1) as the causal floral repressor. We demonstrate that exceptionally low temperatures are needed to downregulate FvTFL1 and to make these plants competent to induce flowering at low postvernalisation temperatures in the spring. We show that altered regulation of FvTFL1 in the northern Norwegian woodland strawberry accession postpones flower induction until the spring, allowing plants to avoid winter injuries of flower buds that commonly occur in temperate regions.

Occupational respiratory allergy in peach crop workers

BACKGROUND

Occupational respiratory diseases in workers of peach tree crops have been reported punctually and have been associated with sensitization to proteins present in both pollen and leaf tree. We report the study of 37 workers with respiratory symptoms related to occupational exposure to peach trees.

METHODS

Prick tests and specific IgE determinations were performed with extracts from leaves and branches of peach tree. Immunodetection in leaf extract was realized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis SDS-PAGE-immunoblotting with patient sera and rabbit serum anti-Pru p 3. Immunodetection inhibition was performed with rPru p 3 and pollen profilins. The clinical relevance of sensitization was demonstrated by specific bronchial challenge test (SBCT) with peach leaf extract.

RESULTS

Most patients suffered symptoms when peach trees had leaves, specifically during thinning and harvesting fruit (rhinoconjunctivitis: 100% and asthma: 67.5%). Sensitization to leaf extract was demonstrated in 86% of patients. IgE-immunoblotting with peach leaf extract revealed in six patient sera a pair of bands of 10 and 16 kDa, and in nine a 16-kDa band. Those bands could be two isoforms of peach leaf lipid transfer proteins( LTP), so the recognition frequency of some LTP isoform by our patient sera was 42%. 33% of the sera recognized a doubled band of about 14.5 kDa and this recognition was inhibited by nPho d 2. The SBCT with peach leaf extract was positive in the asthmatic sensitized patients tested.

CONCLUSIONS

Sensitization to peach leaves was the cause of occupational respiratory symptoms in our patients. Some patient sera revealed IgE-binding proteins matching LTP and/or profilin.

De novo transcriptome analysis in Dendrobium and identification of critical genes associated with flowering

Artificial control of flowering time is pivotal for the ornamental value of orchids including the genus Dendrobium. Although various flowering pathways have been revealed in model plants, little information is available on the genetic regualtion of flowering in Dendrobium. To identify the critical genes associated with flowering, transcriptomes from four organs (leaf, root, stem and flower) of D. officinale were analyzed in our study. In total, 2645 flower-specific transcripts were identified. Functional annotation and classification suggested that several metabolic pathways, including four sugar-related pathways and two fatty acid-related pathways, were enriched. A total of 24 flowering-related transcripts were identified in D. officinale according to the similarities to their homologous genes from Arabidopsis, suggesting that most classical flowering pathways existed in D. officinale. Furthermore, phylogenetic analysis suggested that the FLOWERING LOCUS T homologs in orchids are highly conserved during evolution process. In addition, expression changes in nine randomly-selected critical flowering-related transcripts between the vegetative stage and reproductive stage were quantified by qRT-PCR analysis. Our study provided a number of candidate genes and sequence resources for investigating the mechanisms underlying the flowering process of the Dendrobium genus.

Genetic control of flowering time in woody plants: Roses as an emerging model

Genetic control of the timing of flowering in woody plants is complex and has yet to be adequately investigated due to their long life-cycle and difficulties in genetic modification. Studies in Populus, one of the best woody plant models, have revealed a highly conserved genetic network for flowering timing in annuals. However, traits like continuous flowering cannot be addressed with Populus. Roses and strawberries have relatively small, diploid genomes and feature enormous natural variation. With the development of new genetic populations and genomic tools, roses and strawberries have become good models for studying the molecular mechanisms underpinning the regulation of flowering in woody plants. Here, we review findings on the molecular and genetic factors controlling continuous flowering in roses and woodland strawberries. Natural variation at TFL1 orthologous genes in both roses and strawberries seems be the key plausible factor that regulates continuous flowering. However, recent efforts suggest that a two-recessive-loci model may explain the controlling of continuous flowering in roses. We propose that epigenetic factors, including non-coding RNAs or chromatin-related factors, might also play a role. Insights into the genetic control of flowering time variation in roses should benefit the development of new germplasm for woody crops and shed light on the molecular genetic bases for the production and maintenance of plant biodiversity.

Small RNA-Sequencing Links Physiological Changes and RdDM Process to Vegetative-to-Floral Transition in Apple

Transition from vegetative to floral buds is a critical physiological change during flower induction that determines fruit productivity. Small non-coding RNAs (sRNAs) including microRNAs (miRNAs) and small interfering RNAs (siRNAs) are pivotal regulators of plant growth and development. Although the key role of sRNAs in flowering regulation has been well-described in Arabidopsis and some other annual plants, their relevance to vegetative-to-floral transition (hereafter, referred to floral transition) in perennial woody trees remains under defined. Here, we performed Illumina sequencing of sRNA libraries prepared from vegetative and floral bud during flower induction of the apple trees. A large number of sRNAs exemplified by 33 previously annotated miRNAs and six novel members display significant differential expression (DE) patterns. Notably, most of these DE-miRNAs in floral transition displayed opposite expression changes in reported phase transition in apple trees. Bioinformatics analysis suggests most of the DE-miRNAs targeted transcripts involved in SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) gene regulation, stress responses, and auxin and gibberellin (GA) pathways, with further suggestion that there is an inherent link between physiological stress response and metabolism reprogramming during floral transition. We also observed significant changes in 24 nucleotide (nt) sRNAs that are hallmarks for RNA-dependent DNA methylation (RdDM) pathway, suggestive of the correlation between epigenetic modifications and the floral transition. The study not only provides new insight into our understanding of fundamental mechanism of poorly studied floral transition in apple and other woody plants, but also presents important sRNA resource for future in-depth research in the apple flowering physiology.

Additive QTLs on three chromosomes control flowering time in woodland strawberry (Fragaria vesca L.)

Flowering time is an important trait that affects survival, reproduction and yield in both wild and cultivated plants. Therefore, many studies have focused on the identification of flowering time quantitative trait locus (QTLs) in different crops, and molecular control of this trait has been extensively investigated in model species. Here we report the mapping of QTLs for flowering time and vegetative traits in a large woodland strawberry mapping population that was phenotyped both under field conditions and in a greenhouse after flower induction in the field. The greenhouse experiment revealed additive QTLs in three linkage groups (LG), two on both LG4 and LG7, and one on LG6 that explain about half of the flowering time variance in the population. Three of the QTLs were newly identified in this study, and one co-localized with the previously characterized FvTFL1 gene. An additional strong QTL corresponding to previously mapped PFRU was detected in both field and greenhouse experiments indicating that gene(s) in this locus can control the timing of flowering in different environments in addition to the duration of flowering and axillary bud differentiation to runners and branch crowns. Several putative flowering time genes were identified in these QTL regions that await functional validation. Our results indicate that a few major QTLs may control flowering time and axillary bud differentiation in strawberries. We suggest that the identification of causal genes in the diploid strawberry may enable fine tuning of flowering time and vegetative growth in the closely related octoploid cultivated strawberry.

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.

An apple rootstock overexpressing a peach CBF gene alters growth and flowering in the scion but does not impact cold hardiness or dormancy

The C-repeat binding factor (CBF) transcription factor is involved in responses to low temperature and water deficit in many plant species. Overexpression of CBF genes leads to enhanced freezing tolerance and growth inhibition in many species. The overexpression of a peach CBF (PpCBF1) gene in a transgenic line of own-rooted apple (Malus×domestica) M.26 rootstock (T166) trees was previously reported to have additional effects on the onset of dormancy and time of spring budbreak. In the current study, the commercial apple cultivar 'Royal Gala' (RG) was grafted onto either non-transgenic M.26 rootstocks (RG/M.26) or transgenic M.26 (T166) rootstocks (RG/T166) and field grown for 3 years. No PpCBF1 transcript was detected in the phloem or cambium of RG scions grafted on T166 rootstocks indicating that no graft transmission of transgene mRNA had occurred. In contrast to own-rooted T166 trees, no impact of PpCBF1 overexpression in T166 rootstocks was observed on the onset of dormancy, budbreak or non-acclimated leaf-cold hardiness in RG/T166 trees. Growth, however, as measured by stem caliper, current-year shoot extension and overall height, was reduced in RG/T166 trees compared with RG/M.26 trees. Although flowering was evident in both RG/T166 and RG/M.26 trees in the second season, the number of trees in flower, the number of shoots bearing flowers, and the number of flower clusters per shoot was significantly higher in RG/M.26 trees than RG/T166 trees in both the second and third year after planting. Elevated levels of RGL (DELLA) gene expression were observed in RG/T166 trees and T166 trees, which may play a role in the reduced growth observed in these tree types. A model is presented indicating how CBF overexpression in a rootstock might influence juvenility and flower abundance in a grafted scion.

Analysis of transcripts differentially expressed between fruited and deflowered 'Gala' adult trees: a contribution to biennial bearing understanding in apple

BACKGROUND

The transition from vegetative to floral state in shoot apical meristems (SAM) is a key event in plant development and is of crucial importance for reproductive success. In perennial plants, this event is recurrent during tree life and subject to both within-tree and between-years heterogeneity. In the present study, our goal was to identify candidate processes involved in the repression or induction of flowering in apical buds of adult apple trees.

RESULTS

Genes differentially expressed (GDE) were examined between trees artificially set in either 'ON' or 'OFF' situation, and in which floral induction (FI) was shown to be inhibited or induced in most buds, respectively, using qRT-PCR and microarray analysis. From the period of FI through to flower differentiation, GDE belonged to four main biological processes (i) response to stimuli, including response to oxidative stress; (ii) cellular processes, (iii) cell wall biogenesis, and (iv) metabolic processes including carbohydrate biosynthesis and lipid metabolic process. Several key regulator genes, especially TEMPRANILLO (TEM), FLORAL TRANSITION AT MERISTEM (FTM1) and SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) were found differentially expressed. Moreover, homologs of SPL and Leucine-Rich Repeat proteins were present under QTL zones previously detected for biennial bearing.

CONCLUSIONS

This data set suggests that apical buds of 'ON' and 'OFF' trees were in different physiological states, resulting from different metabolic, hormonal and redox status which are likely to contribute to FI control in adult apple trees. Investigations on carbohydrate and hormonal fluxes from sources to SAM and on cell detoxification process are expected to further contribute to the identification of the underlying physiological mechanisms of FI in adult apple trees.

Shoot bending promotes flower bud formation by miRNA-mediated regulation in apple (Malus domestica Borkh.)

Flower induction in apple (Malus domestica Borkh.) trees plays an important life cycle role, but young trees produce fewer and inferior quality flower buds. Therefore, shoot bending has become an important cultural practice, significantly promoting the capacity to develop more flower buds during the growing seasons. Additionally, microRNAs (miRNAs) play essential roles in plant growth, flower induction and stress responses. In this study, we identified miRNAs potentially involved in the regulation of bud growth, and flower induction and development, as well as in the response to shoot bending. Of the 195 miRNAs identified, 137 were novel miRNAs. The miRNA expression profiles revealed that the expression levels of 68 and 27 known miRNAs were down-regulated and up-regulated, respectively, in response to shoot bending, and that the 31 differentially expressed novel miRNAs between them formed five major clusters. Additionally, a complex regulatory network associated with auxin, cytokinin, abscisic acid (ABA) and gibberellic acid (GA) plays important roles in cell division, bud growth and flower induction, in which related miRNAs and targets mediated regulation. Among them, miR396, 160, 393, and their targets associated with AUX, miR159, 319, 164, and their targets associated with ABA and GA, and flowering-related miRNAs and genes, regulate bud growth and flower bud formation in response to shoot bending. Meanwhile, the flowering genes had significantly higher expression levels during shoot bending, suggesting that they are involved in this regulatory process. This study provides a framework for the future analysis of miRNAs associated with multiple hormones and their roles in the regulation of bud growth, and flower induction and formation in response to shoot bending in apple trees.

Transcription Profiles Reveal Sugar and Hormone Signaling Pathways Mediating Flower Induction in Apple (Malus domestica Borkh.)

Flower induction in apple (Malus domestica Borkh.) is regulated by complex gene networks that involve multiple signal pathways to ensure flower bud formation in the next year, but the molecular determinants of apple flower induction are still unknown. In this research, transcriptomic profiles from differentiating buds allowed us to identify genes potentially involved in signaling pathways that mediate the regulatory mechanisms of flower induction. A hypothetical model for this regulatory mechanism was obtained by analysis of the available transcriptomic data, suggesting that sugar-, hormone- and flowering-related genes, as well as those involved in cell-cycle induction, participated in the apple flower induction process. Sugar levels and metabolism-related gene expression profiles revealed that sucrose is the initiation signal in flower induction. Complex hormone regulatory networks involved in cytokinin (CK), abscisic acid (ABA) and gibberellic acid pathways also induce apple flower formation. CK plays a key role in the regulation of cell formation and differentiation, and in affecting flowering-related gene expression levels during these processes. Meanwhile, ABA levels and ABA-related gene expression levels gradually increased, as did those of sugar metabolism-related genes, in developing buds, indicating that ABA signals regulate apple flower induction by participating in the sugar-mediated flowering pathway. Furthermore, changes in sugar and starch deposition levels in buds can be affected by ABA content and the expression of the genes involved in the ABA signaling pathway. Thus, multiple pathways, which are mainly mediated by crosstalk between sugar and hormone signals, regulate the molecular network involved in bud growth and flower induction in apple trees.

Changing the spatial pattern of TFL1 expression reveals its key role in the shoot meristem in controlling Arabidopsis flowering architecture

Models for the control of above-ground plant architectures show how meristems can be programmed to be either shoots or flowers. Molecular, genetic, transgenic, and mathematical studies have greatly refined these models, suggesting that the phase of the shoot reflects different genes contributing to its repression of flowering, its vegetativeness ('veg'), before activators promote flower development. Key elements of how the repressor of flowering and shoot meristem gene TFL1 acts have now been tested, by changing its spatiotemporal pattern. It is shown that TFL1 can act outside of its normal expression domain in leaf primordia or floral meristems to repress flower identity. These data show how the timing and spatial pattern of TFL1 expression affect overall plant architecture. This reveals that the underlying pattern of TFL1 interactors is complex and that they may be spatially more widespread than TFL1 itself, which is confined to shoots. However, the data show that while TFL1 and floral genes can both act and compete in the same meristem, it appears that the main shoot meristem is more sensitive to TFL1 rather than floral genes. This spatial analysis therefore reveals how a difference in response helps maintain the 'veg' state of the shoot meristem.

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.

Florigen and anti-florigen - a systemic mechanism for coordinating growth and termination in flowering plants

Genetic studies in Arabidopsis established FLOWERING LOCUS T (FT) as a key flower-promoting gene in photoperiodic systems. Grafting experiments established unequivocal one-to-one relations between SINGLE FLOWER TRUSS (SFT), a tomato homolog of FT, and the hypothetical florigen, in all flowering plants. Additional studies of SFT and SELF PRUNING (SP, homolog of TFL1), two antagonistic genes regulating the architecture of the sympodial shoot system, have suggested that transition to flowering in the day-neutral and perennial tomato is synonymous with "termination." Dosage manipulation of its endogenous and mobile, graft-transmissible levels demonstrated that florigen regulates termination and transition to flowering in an SP-dependent manner and, by the same token, that high florigen levels induce growth arrest and termination in meristems across the tomato shoot system. It was thus proposed that growth balances, and consequently the patterning of the shoot systems in all plants, are mediated by endogenous, meristem-specific dynamic SFT/SP ratios and that shifts to termination by changing SFT/SP ratios are triggered by the imported florigen, the mobile form of SFT. Florigen is a universal plant growth hormone inherently checked by a complementary antagonistic systemic system. Thus, an examination of the endogenous functions of FT-like genes, or of the systemic roles of the mobile florigen in any plant species, that fails to pay careful attention to the balancing antagonistic systems, or to consider its functions in day-neutral or perennial plants, would be incomplete.

Effect of extending the photoperiod with low-intensity red or far-red light on the timing of shoot elongation and flower-bud formation of 1-year-old Japanese pear (Pyrus pyrifolia)

To investigate the effects of light quality (wavelength) on shoot elongation and flower-bud formation in Japanese pear (Pyrus pyrifolia (Burm. f.) Nakai), we treated 1-year-old trees with the following: (i) 8 h sunlight + 16 h dark (SD); (ii) 8 h sunlight + 16 h red light (LD(SD + R)); or (iii) 8 h sunlight + 16 h far-red (FR) light (LD(SD + FR)) daily for 4 months from early April (before the spring flush) until early August in 2009 and 2010. In both years, shoot elongation stopped earlier in the LD(SD + FR) treatment than in the SD and LD(SD + R) treatments. After 4 months of treatments, 21% (2009) or 40% (2010) of LD(SD + FR)-treated trees formed flower buds in the shoot apices, whereas all the shoot apices from SD or LD(SD + R)-treated plants remained vegetative. With an additional experiment conducted in 2012, we confirmed that FR light at 730 nm was the most efficacious wavelength to induce flower-bud formation. Reverse transcription-quantitative polymerase chain reaction revealed that the expression of two floral meristem identity gene orthologues, LEAFY (PpLFY2a) and APETALA1 (PpMADS2-1a), were up-regulated in the shoot apex of LD(SD + FR). In contrast, the expression of a flowering repressor gene, TERMINAL FLOWER 1 (PpTFL1-1a, PpTFL1-2a), was down-regulated. In addition, expression of an orthologue of the flower-promoting gene FLOWERING LOCUS T (PpFT1a) was positively correlated with flower-bud formation, although the expression of another orthologue, PpFT2a, was negatively correlated with shoot growth. Biologically active cytokinin and gibberellic acid concentrations in shoot apices were reduced with LD(SD + FR) treatment. Taken together, our results indicate that pear plants are able to regulate flowering in response to the R : FR ratio. Furthermore, LD(SD + FR) treatment terminated shoot elongation and subsequent flower-bud formation in the shoot apex at an earlier time, possibly by influencing the expression of flowering-related genes and modifying plant hormone concentrations.

Light quality regulates flowering in FvFT1/FvTFL1 dependent manner in the woodland strawberry Fragaria vesca

Control of flowering in the perennial model, the woodland strawberry (Fragaria vesca L.), involves distinct molecular mechanisms that result in contrasting photoperiodic flowering responses and growth cycles in different accessions. The F. vesca homolog of TERMINAL FLOWER1 (FvTFL1) functions as a key floral repressor that causes short-day (SD) requirement of flowering and seasonal flowering habit in the SD strawberry. In contrast, perpetual flowering F. vesca accessions lacking functional FvTFL1 show FLOWERING LOCUS T (FvFT1)-dependent early flowering specifically under long-days (LD). We show here that the end-of-day far-red (FR) and blue (B) light activate the expression of FvFT1 and the F. vesca homolog of SUPPRESSOR OF THE OVEREXPRESSION OF CONSTANS (FvSOC1) in both SD and LD strawberries, whereas low expression levels are detected in red (R) and SD treatments. By using transgenic lines, we demonstrate that FvFT1 advances flowering under FR and B treatments compared to R and SD treatments in the LD strawberry, and that FvSOC1 is specifically needed for the B light response. In the SD strawberry, flowering responses to these light quality treatments are reversed due to up-regulation of the floral repressor FvTFL1 in parallel with FvFT1 and FvSOC1. Our data highlights the central role of FvFT1 in the light quality dependent flower induction in the LD strawberry and demonstrates that FvTFL1 reverses not only photoperiodic requirements but also light quality effects on flower induction in the SD strawberry.