Long-day Flowering Research Articles

Spectrum of low-intensity screw-in horticultural light-emitting diode lamps influences time to flower and finished quality of long-day ornamental species

Bedding plants with a long-day (LD) flowering requirement constitute a substantial portion of annuals and perennials produced in the United States for spring sales. However, greenhouse production often occurs when the day length is naturally short and not conducive for flower induction of LD plants (LDPs). Thus, growers must create artificial LDs through day-extension, cyclic, or night-interruption (NI) lighting to promote flowering of LDPs. Many low-intensity, screw-in horticultural light-emitting diode (LED) lamps are now commercially available, though their emission spectra vary. Therefore, the objective of our study was to quantify the influence of various commercially available low-intensity screw-in horticultural LED lamps on the flowering and growth responses of LDPs. We grew several obligate and facultative LD annuals under either a 9-h truncated short-day (SD), or a 9-h SD with NI lighting from 2200 to 0200 hr each day. NI treatments consisted of Feit 9-W Non-Dimmable Plant Grow Lights (Feit), General Electric (GE) 10-W Arize™ Greenhouse Pro-Photoperiodic LED Lamps (GE), Philips 13-W GreenPower LED flowering lamp 2.0 s (Philips), or TotalGrow ™ 16-W Pure Flowering 200 Lamps (TotalGrow). Philips and GE lamps hastened flowering of all LDPs studied, while TotalGrow lamps promoted or hastened flowering on a genus-specific basis. Flowering was delayed by up to 11 d under Feit lamps and plants developed more nodes and inflorescences at open flower than the other lighting treatments. Generally, the height of plants within genera were similar regardless of the lighting treatment. However, plants grown under TotalGrow lamps had a larger stem length than those grown under the other lighting treatments as they emitted the highest percentage of FR light. Therefore, greenhouse growers should not base their decision solely on the price of lamps.

PHYTOCHROME C regulation of photoperiodic flowering via PHOTOPERIOD1 is mediated by EARLY FLOWERING 3 in Brachypodium distachyon.

Daylength sensing in many plants is critical for coordinating the timing of flowering with the appropriate season. Temperate climate-adapted grasses such as Brachypodium distachyon flower during the spring when days are becoming longer. The photoreceptor PHYTOCHROME C is essential for long-day (LD) flowering in B. distachyon. PHYC is required for the LD activation of a suite of genes in the photoperiod pathway including PHOTOPERIOD1 (PPD1) that, in turn, result in the activation of FLOWERING LOCUS T (FT1)/FLORIGEN, which causes flowering. Thus, B. distachyon phyC mutants are extremely delayed in flowering. Here we show that PHYC-mediated activation of PPD1 occurs via EARLY FLOWERING 3 (ELF3), a component of the evening complex in the circadian clock. The extreme delay of flowering of the phyC mutant disappears when combined with an elf3 loss-of-function mutation. Moreover, the dampened PPD1 expression in phyC mutant plants is elevated in phyC/elf3 mutant plants consistent with the rapid flowering of the double mutant. We show that loss of PPD1 function also results in reduced FT1 expression and extremely delayed flowering consistent with results from wheat and barley. Additionally, elf3 mutant plants have elevated expression levels of PPD1, and we show that overexpression of ELF3 results in delayed flowering associated with a reduction of PPD1 and FT1 expression, indicating that ELF3 represses PPD1 transcription consistent with previous studies showing that ELF3 binds to the PPD1 promoter. Indeed, PPD1 is the main target of ELF3-mediated flowering as elf3/ppd1 double mutant plants are delayed flowering. Our results indicate that ELF3 operates downstream from PHYC and acts as a repressor of PPD1 in the photoperiod flowering pathway of B. distachyon.

Cantil: a previously unreported organ in wild-type Arabidopsis regulated by FT, ERECTA and heterotrimeric G proteins.

We describe a previously unreported macroscopic Arabidopsis organ, the cantil, named for its 'cantilever' function of holding the pedicel at a distance from the stem. Cantil development is strongest at the first nodes after the vegetative to reproductive inflorescence transition; cantil magnitude and frequency decrease acropetally. Cantils develop in wild-type Arabidopsis accessions (e.g. Col-0, Ws and Di-G) as a consequence of delayed flowering in short days; cantil formation is observed in long days when flowering is delayed by null mutation of the floral regulator FLOWERING LOCUS T. The receptor-like kinase ERECTA is a global positive regulator of cantil formation; therefore, cantils never form in the Arabidopsis strain Ler. ERECTA functions genetically upstream of heterotrimeric G proteins. Cantil expressivity is repressed by the specific heterotrimeric complex subunits GPA1, AGB1 and AGG3, which also play independent roles: GPA1 suppresses distal spurs at cantil termini, while AGB1 and AGG3 suppress ectopic epidermal rippling. These G protein mutant traits are recapitulated in long-day flowering gpa1-3 ft-10 plants, demonstrating that cantils, spurs and ectopic rippling occur as a function of delayed phase transition, rather than as a function of photoperiod per se.

Phosphorylation of OsFD1 by OsCIPK3 promotes the formation of RFT1-containing florigen activation complex for long-day flowering in rice

Heading date is a critical trait that determines the regional adaptability and grain productivity of many crops. Although rice is a facultative short-day plant, its domestication led to the Ghd7-Ehd1-Hd3a/RFT1 pathway for adaptation to long-day conditions (LDs). The formation of the “florigen activation complex” (FAC) containing florigen Hd3a has been characterized. However, the molecular composition of the FAC that contains RFT1 for long-day flowering is unclear. We show here that RFT1 forms a ternary FAC with 14-3-3 proteins and OsFD1 to promote flowering under LDs. We identified a calcineurin B-like-interacting protein kinase, OsCIPK3, which directly interacts with and phosphorylates OsFD1, thereby facilitating the localization of the FAC to the nucleus. Mutation in OsCIPK3 results in a late heading date under LDs but a normal heading date under short-day conditions. Collectively, our results suggest that OsCIPK3 phosphorylates OsFD1 to promote RFT1-containing FAC formation and consequently induce flowering in rice under LDs.

Evolution: Replicated mutation of COL2 contributed long-day flowering in common bean

The ability to flower without strict daylength constraints has helped spread cultivation of crop plants to new locations. The generation of daylength-insensitive common bean accessions in central and South America involved the repeated selection of mutant alleles for a key transcription factor that suppresses long-day flowering.

Changing times: Opportunities for altering winter wheat phenology

Social Impact StatementClimate change presents challenges to agricultural production systems. Wheat is a significant crop in the United Kingdom, occupying 40% of arable land area. Increased temperatures and drought risk are predicted to lead to future productivity losses. Plant breeders and researchers are working to develop more resilient wheat varieties although are often driven by different motivating factors compared to farmers. Here, we report on a dialog with agronomists working with farmers in wheat‐producing regions throughout the UK to gain greater understanding of the farm‐level importance of wheat flowering time and maturity along with the future opportunities and risks presented by earlier flowering varieties. Summary Optimized environmental adaptation is the cornerstone of regional crop breeding. Recent and predicted future instability for long‐standing adaptive response presents new challenges to selective breeding. Wheat is a long day plant, requiring extended daylength to initiate flowering, a response controlled by the Photoperiod‐1 (Ppd‐1) gene. Mutations conferring photoperiod insensitivity arose during domestication, allowing rapid flowering in both short and long days and extending wheat's adaptive range. In the United Kingdom, wheat production is dominated by photoperiod‐sensitive winter varieties which have a relatively narrow window of flowering time. Changing seasonal conditions alongside mounting logistics pressure as a result of loss of effective agrochemicals and increasing seasonal weather fluctuations mean that greater flexibility in varietal flowering time is likely required to sustain UK wheat productivity. In this Opinion piece, we present findings from a recent dialog with UK agronomists on the demand and likely potential for greater flowering time range in winter wheat varieties. This provides important insight connecting farmer priorities and demands with ongoing genetic research and breeding. Our findings highlight the farm‐level importance of wheat phenology and provide recommendations for future research and plant breeding.

A Combination of Long-Day Suppressor Genes Contributes to the Northward Expansion of Rice.

Growing cultivated rice with a moderate heading date is the key to expanding its cultivation area and maintaining stable yields. The genes that regulate heading date are largely cloned; however, it remains unclear how genetic mutations and their combinations affect the heading date and adaptability of cultivated rice. Here, we report the analysis of genetic variation in eight long-day flowering suppressor genes (Hd1, DTH8, Ghd7, OsCOL4, DTH7, Hd6, Se5, and PhyB) and the phylogenetic relationship of eight genes. Genetic variations in DTH8, Ghd7, Hd1, DTH7, PhyB, and OsCOL4 are correlated with differences in heading date and the correlation between the genetic diversity of Hd6 and Se5 and rice heading data are weak. One group of haplotypes of DTH8, Ghd7, Hd1, DTH7, PhyB, and OsCOL4 are associated with earlier heading dates and appear to have accumulated during the northward expansion of rice cultivation. A minimum of four group A alleles of DTH8, Ghd7, Hd1, DTH7, PhyB, and OsCOL4 are required for the growth of cultivated rice at latitudes above 30°N. This study presents a preliminary investigation of the genetic patterns and adaptation mechanisms of long-day flowering suppressor genes and provides a useful reference for the molecular breeding of rice cultivars for various environments and farming systems.

SIN3 LIKE genes mediate long-day induction of flowering but inhibit the floral transition in short days through histone deacetylation in Arabidopsis.

Day length or photoperiod changes are crucial for plants to align the timing of the floral transition with seasonal changes. Through the photoperiod pathway, day length changes induce the expression of the florigenic FLOWERING LOCUS T (FT) to promote flowering. In the facultative long days (LDs) plant Arabidopsis thaliana, LD signals induce flowering, whereas short days (SDs) inhibit flowering. Here, we show that in Arabidopsis SIN3 LIKE (SNL) family genes, encoding a scaffold protein for assembly of histone deacetylase complexes, directly repress the expression of an FT activator and three FT repressors to regulate the transition to flowering in SDs and LDs, respectively. Under inductive LDs, SNLs including SIN3 LIKE 1 (SNL1) to SNL5, function in partial redundancy to repress the expression of three AP2 family transcription factors that repress FT expression, and therefore mediate LD induction of FT expression and promote the transition to flowering. In contrast, under non-inductive SDs SNLs act to inhibit the floral transition, partly through direct repression of a MADS box transcriptional factor that promotes FT expression. Therefore, our results reveal that SNLs, through histone deacetylation, play a dual role for the control of flowering in the LD plant Arabidopsis: inhibiting flowering when the day length is shorter and promoting the floral transition when days become longer than a threshold length.

Growth and Flowering Response of <i>Patrinia rupestris</i> in Response to Different Cold Durations and Photoperiods

This study aims to examine the effects of cold durations and photoperiods on dormancy break, growth, and flowering of Patrinia rupestris native to Korea. First, we monitored the growth and flowering phenology of plants growing in an open field from March to October, 2018. For the dormancy breaking experiments, P. rupestris was maintained at 4°C for 0, 3, 6, 9, and 12 weeks under short-day conditions andfor cold treatment. The plants were then transferred to long-day conditions (9 h + 4h night interruption) in room chamber set at 25°C. To determine photoperiodic responses, P. rupestris was maintained under short- (9 h, SD), middle- (12 h, MD), and long-day (16 h, LD) conditions in room chamber set at 25°C following natural chilling accumulation. In open field conditions, P. rupestris blooms in the late summer from August to September with attractive yellow flowers. Time to first flower significantly decreased following 9 or 12 weeks of cold storage compared with the plants subjected to 3 or 6 weeks of cold storage. P. rupestris required ≥9 weeks of chilling treatment to achieve ≥33% flowering. Plant height was the highest in the LD condition (50.1 cm) compared with the SD (16.7 cm) and MD (16.1 cm) conditions. All plants grown under LD conditions flowered, but not all plants grown under SD and MD conditions did (0% flowering) after 16 weeks of forcing. P. rupestris demonstrated both obligate vernalization and long-day flowering responses.

Maturity2, a novel regulator of flowering time in Sorghum bicolor, increases expression of SbPRR37 and SbCO in long days delaying flowering.

Sorghum bicolor is a drought-resilient facultative short-day C4 grass that is grown for grain, forage, and biomass. Adaptation of sorghum for grain production in temperate regions resulted in the selection of mutations in Maturity loci (Ma1 –Ma6) that reduced photoperiod sensitivity and resulted in earlier flowering in long days. Prior studies identified the genes associated with Ma1 (PRR37), Ma3 (PHYB), Ma5 (PHYC) and Ma6 (GHD7) and characterized their role in the flowering time regulatory pathway. The current study focused on understanding the function and identity of Ma2. Ma2 delayed flowering in long days by selectively enhancing the expression of SbPRR37 (Ma1) and SbCO, genes that co-repress the expression of SbCN12, a source of florigen. Genetic analysis identified epistatic interactions between Ma2 and Ma4 and located QTL corresponding to Ma2 on SBI02 and Ma4 on SBI10. Positional cloning and whole genome sequencing identified a candidate gene for Ma2, Sobic.002G302700, which encodes a SET and MYND (SYMD) domain lysine methyltransferase. Eight sorghum genotypes previously identified as recessive for Ma2 contained the mutated version of Sobic.002G302700 present in 80M (ma2) and one additional putative recessive ma2 allele was identified in diverse sorghum accessions.

Water use efficiency, photosynthesis and plant growth of Chia (Salvia hispanica L.): a glasshouse experiment

As chia (Salvia hispanica L.) is spreading in new environments, information on its photosynthetic and agronomic behavior is scarce. This research is focused on the physiological characteristics (photosynthetic rate, conductance to H2O, transpiration rate, intercellular CO2 concentration) of chia with different water supply and from two sources: a commercial Black chia (P) and a long-day flowering mutant (G8). Irrigation treatments were: full (V100) with soil water restitution up to field capacity, half (V50) where half of the water of V100 was given, and no irrigation (VO). Water shortage reduced the photosynthetic rate by 25% between V100 and V0; transpiration was reduced significantly only in the P genotype between V100 and V0 by 52%. Leaf water potentials ranged between − 1.1 (V100) and − 2.0 (V0). Leaf area and total dry matter decreased significantly in response to water shortage due to reduced photosynthetic activity and lower water availability. The G8 genotype showed higher photosynthetic rate, but lower leaf water potential and overall biomass accumulation and leaf area than the P genotype. According to our results Water Use Efficiency increased with water availability and was higher in the P genotype at all irrigation levels, ranging from 0.5 g l−1 in G8 V0 to 1.5 g l−1 in P V100.

Soil structure and stability in the spermosphere of myxosdiaspore chia (Salvia hispanica L.)

Mucilage produced by myxodiaspores has been mainly studied for its role in seed ecology. This work investigates changes due to mucilage in soil structure and stability in the spermosphere of the myxodiaspore crop chia (Salvia hispanica L.). In sandy-loam (S) repacked soil sown with chia and subjected to wetting–drying (DW), Computer Assisted X-ray micro tomography showed that extrusion of a mucilage capsule formed a pore of volume twice that of the seed, surrounded by a shell of particles with higher porosity and lower pore size than the bulk soil. In three soils (S; loam, L; and clay-loam, C) the aggregate stability index to wet sieving (Stw) decreased with one and two DW cycles. Application of 2% w/w mucilage increased Stw before and after DW, from 29% in C to more than 60-fold in S. Mucilage-amended samples after DW had higher or equal Stw compared with unamended soil before DW. Soil retained at the surface of hydrated diaspores exposed to water flow changed with soil texture (11.3, 90.5 and 91.7mg on each hydrated seed for S, L and C respectively) and chia genotype (6.7, 9.9 and 12.8mg per hydrated seed in BC and G8 long-day flowering mutants and commercial Black chia respectively). Our results showed that myxodiaspores affected soil structure by providing a microenvironment of altered porosity and high stability around the mucilage capsule extruded by the hydrated seed. This finding characterises a transient but crucial time of crop production around sowing when physical properties of soil surrounding seeds are relevant to stability, germination and plant–microorganism relations.

Overexpression of PvCO1, a bamboo CONSTANS-LIKE gene, delays flowering by reducing expression of the FT gene in transgenic Arabidopsis

BackgroundIn Arabidopsis, a long day flowering plant, CONSTANS (CO) acts as a transcriptional activator of flowering under long day (LD) condition. In rice, a short day flowering plant, Hd1, the ortholog of CO, plays dual functions in respond to day-length, activates flowering in short days and represses flowering in long days. In addition, alleles of Hd1 account for ~ 44% of the variation in flowering time observed in cultivated rice and sorghum. How does it work in bamboo? The function of CO in bamboo is similar to that in Arabidopsis?ResultsTwo CO homologous genes, PvCO1 and PvCO2, in Phyllostachys violascens were identified. Alignment analysis showed that the two PvCOLs had the highest sequence similarity to rice Hd1. Both PvCO1 and PvCO2 expressed in specific tissues, mainly in leaf. The PvCO1 gene had low expression before flowering, high expression during the flowering stage, and then declined to low expression again after flowering. In contrast, expression of PvCO2 was low during the flowering stage, but rapidly increased to a high level after flowering. The mRNA levels of both PvCOs exhibited a diurnal rhythm. Both PvCO1 and PvCO2 proteins were localized in nucleus of cells. PvCO1 could interact with PvGF14c protein which belonged to 14–3-3 gene family through B-box domain. Overexpression of PvCO1 in Arabidopsis significantly caused late flowering by reducing the expression of AtFT, whereas, transgenic plants overexpressing PvCO2 showed a similar flowering time with WT under LD conditions. Taken together, these results suggested that PvCO1 was involved in the flowering regulation, and PvCO2 may either not have a role in regulating flowering or act redundantly with other flowering regulators in Arabidopsis. Our data also indicated regulatory divergence between PvCOLs in Ph. violascens and CO in Arabidopsis as well as Hd1 in Oryza sativa. Our results will provide useful information for elucidating the regulatory mechanism of COLs involved in the flowering.ConclusionsUnlike to the CO gene in Arabidopsis, PvCO1 was a negative regulator of flowering in transgenic Arabidopsis under LD condition. It was likely that long period of vegetative growth of this bamboo species was related with the regulation of PvCO1.

Climate warming shortens flowering duration: a comprehensive assessment of plant phenological responses based on gene expression analyses and mathematical modeling

AbstractThere is an increasing potential to incorporate recent advances in our understanding of molecular‐genetic pathways of flowering‐time regulation to forecast shifts in flowering phenology in response to rising temperature. Recent studies developed models that integrate temperature and photoperiod signals into the network of floral regulatory genes, and predicted the shortening of flowering duration under warming based on the expression dynamics of major flowering‐time genes in the perennial herb Arabidopsis halleri subsp. gemmifera. Nevertheless, empirical testing of the model prediction is still lacking. We performed temperature manipulation experiments and common garden experiments to test the model predictions using plants from two distant populations of A. halleri. We also quantified expression levels of two major flowering‐time genes and compared the observed and predicted gene expression patterns. Our experiments in the laboratory and the field demonstrated that flowering duration of A. halleri was significantly shortened under warming conditions. Our results also revealed that the end of flowering was more sensitive to the climate warming than the onset of flowering in A. halleri. The observed gene expression dynamics in the warming condition were predicted well by the gene regulatory model. The transplant experiment of plants from Hokkaido, the northernmost island, to the subtropical field site in Okinawa, Japan, showed that plants flowered without significant activation of FLOWERING LOCUS T, a floral integrator crucial for the accelerated flowering in long days. The study suggested that the redundancy of flowering gene regulatory network could be beneficial to the persistence of flowering ability under extreme climatic conditions.

P-236 - Unravelling the role of DRIF transcription factors in Arabidopsis thaliana

Transcriptions factors play a pivotal role in the regulation of gene expression and in the control of several developmental processes. A new sub-family of transcriptional regulators, called DIV-and-RAD-interacting-factors (DRIFs) participate in an antagonistic module of interactions regulated by a small interfering peptide, and have been co-opted to regulate different developmental processes in plants. It is still unknown what molecular and cellular processes this module controls in Arabidopsis thaliana. Single knockout lines for five DRIF homologs do not show any obvious phenotypes, suggesting genetic redundancy. Double and triple mutants were obtained and are currently being analysed. One phenotype displayed by a triple mutant is late flowering under long days with no observable difference from wild-type plants under short days, suggesting that the DRIFs may be involved in the long-day flowering time pathway. The expression of genes controlling this pathway will be analysed in the triple mutant. Other phenotypes displayed by double and triple mutants are currently being explored and will be presented.

Metabolomic analysis by UAE-GC MS and antioxidant activity of Salvia hispanica (L.) seeds grown under different irrigation regimes

Chia (Salvia hispanica L.) is an emerging crop with a high content of α-linolenic acid and metabolites of industrial and pharmaceutical interest but information on metabolome variations in response to agricultural management is scarce. We investigated the yield and metabolic profile of the seeds of two chia populations, one commercial black (B) and one long-day flowering genotype (G8), in response to two irrigation levels: replacement of 100% ET0 (I) or rainfed (NI). Seed yield was higher in irrigated plots in G8 only (0.255 kg m−2 for I vs 0.184 kg m−2 for NI) while it was very low regardless of irrigation in B due to late flowering. Ultrasound assisted extraction (UAE) of seeds followed by gas chromatography-mass spectrometry (GC/MS) analysis showed differences in fatty acids and the major classes of organic compounds due to both genotype and irrigation, especially in the non-polar phase where irrigated samples showed a higher content of α-linolenic and other fatty acids and a lower oleic/linoleic ratio (47.4 in NI vs. 39.6 in I). The antioxidant activity, expressed as trolox equivalent antioxidant capacity (TEAC), ranged from 1.317 ± 0.027 to 2.174 ± 0.010 mmol TEAC/g of defatted chia seed after 2 and 40 min respectively, and was negatively affected by irrigation. The total polyphenolic content (TPC) measured with the Folin-Ciocalteu method, also decreased with irrigation. According to our results irrigation can affect chia yield, metabolome and antioxidant behavior but some of the effects are genotype-dependent.

Shelf-life evaluation and nutraceutical properties of chia seeds from a recent long-day flowering genotype cultivated in Mediterranean area

Chia seeds (S. hispanica L.) are a good source of nutrients like essential fatty acids, fiber and antioxidant compounds; for this reason they are considered as functional foods. Chia seeds are usually cultivated in Central America, while a few reports about their growing outside of this area are reported. In this paper seeds obtained from a recent G8 genotype, a long-day flowering line of chia, grown in Mediterranean area have been analyzed during storage time to evaluate their oxidative stability and nutraceutical compounds. Seeds were grown with two different levels of irrigation and two levels of sowing density. No significant influence of these factors on chemical composition of seeds has been found. Seed yield was comparable with the one from native area as well as fatty acid composition and antioxidant compounds content, even if a higher content of peroxides and a shorter predicted shelf life was recorded.

Flowering performance and yield of established and recent strawberry cultivars (Fragaria × ananassa) as affected by raising temperature and photoperiod

ABSTRACTPlants of six strawberry cultivars were raised under controlled conditions and tested for flowering and yield potential. Short days (SD) at intermediate temperatures for 4 weeks in August induced profuse flowering in subsequent long days (LD) in all cultivars except the late-flowering ‘Malwina’. LD conditions induced flowering only in ‘Nobel’, which has an everbearing parent. ‘Nobel’ and ‘Saga’ exhibited broad temperature adaptation for SD floral induction, which was generally reduced or suppressed at 9 and 27°C. After autumn planting, all cultivars flowered most abundantly in plants raised in SD and intermediate temperatures. Flowering was earliest in ‘Nobel’ and ‘Rumba’. Plants that did not reach floral commitment after 4 weeks in SD continued and completed induction under subsequent natural SD conditions after planting in the field, demonstrating the capability of fractional induction. Berry yield varied in parallel with flowering in the field and was always higher in plants raised under SD conditions. The traditional cultivars ‘Florence’ and ‘Sonata’ out-yielded the more recent cultivars. Some cultivars lost more than two thirds of their initiated flowers during the winter with obvious consequences for their yields. With proper raising management, acceptable yields were obtained after autumn planting even in a cool Nordic climate.

The sweet cherry (Prunus avium) FLOWERING LOCUS T gene is expressed during floral bud determination and can promote flowering in a winter-annual Arabidopsis accession.

FT gene is expressed in leaves and buds and is involved in floral meristem determination and bud development in sweet cherry. In woody fruit perennial trees, floral determination, dormancy and bloom, depends on perception of different environmental and endogenous cues which converge to a systemic signaling gene known as FLOWERING LOCUS T (FT). In long-day flowering plants, FT is expressed in the leaves on long days. The protein travels through the phloem to the shoot apical meristem, where it induces flower determination. In perennial plants, meristem determination and flowering are separated by a dormancy period. Meristem determination takes place in summer, but flowering occurs only after a dormancy period and cold accumulation during winter. The roles of FT are not completely clear in meristem determination, dormancy release, and flowering in perennial plants. We cloned FT from sweet cherry (Prunus avium) and analyzed its expression pattern in leaves and floral buds during spring and summer. Phylogenetic analysis shows high identity of the FT cloned sequence with orthologous genes from other Rosaceae species. Our results show that FT is expressed in both leaves and floral buds and increases when the daylight reached 12h. The peak in FT expression was coincident with floral meristem identity genes expression and morphological changes typical of floral meristem determination. The Edi-0 Arabidopsis ecotype, which requires vernalization to flower, was transformed with a construct for overexpression of PavFT. These transgenic plants showed an early-flowering phenotype without cold treatment. Our results suggest that FT is involved in floral meristem determination and bud development in sweet cherry. Moreover, we show that FT is expressed in both leaves and floral buds in this species, in contrast to annual plants.

BRR2a Affects Flowering Time via FLC Splicing.

Several pathways control time to flowering in Arabidopsis thaliana through transcriptional and posttranscriptional gene regulation. In recent years, mRNA processing has gained interest as a critical regulator of flowering time control in plants. However, the molecular mechanisms linking RNA splicing to flowering time are not well understood. In a screen for Arabidopsis early flowering mutants we identified an allele of BRR2a. BRR2 proteins are components of the spliceosome and highly conserved in eukaryotes. Arabidopsis BRR2a is ubiquitously expressed in all analyzed tissues and involved in the processing of flowering time gene transcripts, most notably FLC. A missense mutation of threonine 895 in BRR2a caused defects in FLC splicing and greatly reduced FLC transcript levels. Reduced FLC expression increased transcription of FT and SOC1 leading to early flowering in both short and long days. Genome-wide experiments established that only a small set of introns was not correctly spliced in the brr2a mutant. Compared to control introns, retained introns were often shorter and GC-poor, had low H3K4me1 and CG methylation levels, and were often derived from genes with a high-H3K27me3-low-H3K36me3 signature. We propose that BRR2a is specifically needed for efficient splicing of a subset of introns characterized by a combination of factors including intron size, sequence and chromatin, and that FLC is most sensitive to splicing defects.