Photoperiod Perception Research Articles

SPL16 and SPL23 mediate photoperiodic control of seasonal growth in Populus trees.

Perennial trees in boreal and temperate regions undergo growth cessation and bud set under short photoperiods, which are regulated by phytochrome B (phyB) photoreceptors and PHYTOCHROME INTERACTING FACTOR 8 (PIF8) proteins. However, the direct signaling components downstream of the phyB-PIF8 module remain unclear. We found that short photoperiods suppressed the expression of miR156, while upregulated the expression of miR156-targeted SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE 16 (SPL16) and SPL23 in leaves and shoot apices of Populus trees. Accordingly, either overexpression of MIR156a/c or mutagenesis of SPL16/23 resulted in the attenuation of growth cessation and bud set under short days (SD), whereas overexpression of SPL16 and SPL23 conferred early growth cessation. We further showed that SPL16 and SPL23 directly suppressed FLOWERING LOCUS T2 (FT2) expression while promoted BRANCHED1 (BRC1.1 and BRC1.2) expression. Moreover, we revealed that PIF8.1/8.2, positive regulators of growth cessation, directly bound to promoters of MIR156a and MIR156c and inhibited their expression to modulate downstream pathways. Our results reveal a connection between the phyB-PIF8 module-mediated photoperiod perception and the miR156-SPL16/23-FT2/BRC1 regulatory cascades in SD-induced growth cessation. Our study provides insights into the rewiring of a conserved miR156-SPL module in the regulation of seasonal growth in Populus trees.

The evening complex integrates photoperiod signals to control flowering in rice

Plants use photoperiodism to activate flowering in response to a particular daylength. In rice, flowering is accelerated in short-day conditions, and even a brief exposure to light during the dark period (night-break) is sufficient to delay flowering. Although many of the genes involved in controlling flowering in rice have been uncovered, how the long- and short-day flowering pathways are integrated, and the mechanism of photoperiod perception is not understood. While many of the signaling components controlling photoperiod-activated flowering are conserved between Arabidopsis and rice, flowering in these two systems is activated by opposite photoperiods. Here we establish that photoperiodism in rice is controlled by the evening complex (EC). We show that mutants in the EC genes LUX ARRYTHMO (LUX) and EARLY FLOWERING3 (ELF3) paralogs abolish rice flowering. We also show that the EC directly binds and suppresses the expression of flowering repressors, including PRR37 and Ghd7. We further demonstrate that light acts via phyB to cause a rapid and sustained posttranslational modification of ELF3-1. Our results suggest a mechanism by which the EC is able to control both long- and short-day flowering pathways.

Interaction between photoperiod and variation in circadian rhythms in tomato

BackgroundMany biological processes follow circadian rhythmicity and are controlled by the circadian clock. Predictable environmental changes such as seasonal variation in photoperiod can modulate circadian rhythms, allowing organisms to adjust the timing of their biological processes to the time of the year. In some crops such as rice, barley or soybean, mutations in circadian clock genes have altered photoperiod sensitivity, enhancing their cultivability in specific seasons and latitudes. However, how changes in circadian rhythms interact with the perception of photoperiod in crops remain poorly studied. In tomato, the appearance during domestication of mutations in EMPFINDLICHER IM DUNKELROTEN LICHT 1 (EID1, Solyc09g075080) and NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED GENE 2 (LNK2, Solyc01g068560) delayed both the phase and period of its circadian rhythms. The fact that variation in period and phase are separated in tomato provides an optimal tool to study how these factors affect the perception of photoperiod.ResultsHere we develop tomato near isogenic lines carrying combinations of wild alleles of EID1 and LNK2 and show that they recreate the changes in phase and period that occurred during its domestication. We perform transcriptomic profiling of these near isogenic lines under two different photoperiods, and observe that EID1, but not LNK2, has a large effect on how the tomato transcriptome responds to photoperiod. This large effect of EID1 is likely a consequence of the global phase shift elicited by this gene in tomato's circadian rhythms.ConclusionsOur study shows that changes in phase that occurred during tomato domestication determine photoperiod perception in this species, while changes in period have little effect.

LUX ARRHYTHMO Interacts With ELF3a and ELF4a to Coordinate Vegetative Growth and Photoperiodic Flowering in Rice.

The evening complex (EC) plays a critical role in photoperiod flowering in Arabidopsis. Nevertheless, the underlying functions of individual components and coordinate regulation mechanism of EC genes in rice flowering remain to be elucidated. Here, we characterized the critical role of LUX ARRHYTHMO (LUX) in photoperiod perception and coordinating vegetative growth and flowering in rice. Non-functional alleles of OsLUX extremely extended vegetative phase, leading to photoperiod-insensitive late flowering and great increase of grain yield. OsLUX displayed an obvious diurnal rhythm expression with the peak at dusk and promoted rice flowering via coordinating the expression of genes associated with the circadian clock and the output integrators of photoperiodic flowering. OsLUX combined with OsELF4a and OsELF3a or OsELF3b to form two ECs, of which the OsLUX-OsELF3a-OsELF4a was likely the dominant promoter for photoperiodic flowering. In addition, OsELF4a was also essential for promoting rice flowering. Unlike OsLUX, loss OsELF4a displayed a marginal influence under short-day (SD) condition, but markedly delayed flowering time under long-day (LD) condition. These results suggest that rice EC genes share the function of promoting flowering. This is agreement with the orthologs of SD plant, but opposite to the counterparts of LD species. Taken together, rice EC genes display similar but not identical function in photoperiodic flowering, probably through regulating gene expression cooperative and independent. These findings facilitate our understanding of photoperiodic flowering in plants, especially the SD crops.

EARLY FLOWERING 3 and Photoperiod Sensing in Brachypodium distachyon.

The proper timing of flowering, which is key to maximize reproductive success and yield, relies in many plant species on the coordination between environmental cues and endogenous developmental programs. The perception of changes in day length is one of the most reliable cues of seasonal change, and this involves the interplay between the sensing of light signals and the circadian clock. Here, we describe a Brachypodium distachyon mutant allele of the evening complex protein EARLY FLOWERING 3 (ELF3). We show that the elf3 mutant flowers more rapidly than wild type plants in short days as well as under longer photoperiods but, in very long (20 h) days, flowering is equally rapid in elf3 and wild type. Furthermore, flowering in the elf3 mutant is still sensitive to vernalization, but not to ambient temperature changes. Molecular analyses revealed that the expression of a short-day marker gene is suppressed in elf3 grown in short days, and the expression patterns of clock genes and flowering time regulators are altered. We also explored the mechanisms of photoperiodic perception in temperate grasses by exposing B. distachyon plants grown under a 12 h photoperiod to a daily night break consisting of a mixture of red and far-red light. We showed that 2 h breaks are sufficient to accelerate flowering in B. distachyon under non-inductive photoperiods and that this acceleration of flowering is mediated by red light. Finally, we discuss advances and perspectives for research on the perception of photoperiod in temperate grasses.

Night interruption provides evidence for photoperiodic regulation of bud burst in Japanese beech, Fagus crenata

ABSTRACT Some of trees in cool and temperate regions regulate bud burst by perceiving photoperiod. However, it is not clear whether the difference in bud burst timing between the two photoperiod conditions is due to differences in perception of day length or the daily light integral (DLI) because majority of studies concerning the photoperiodic regulation of bud burst make use of an experimental design that compares the differential timing of bud burst between long and shortday length. We conducted night and day interrupt experiments using twig cuttings of Japanese beech, Fagus crenata, to investigate the effect of photoperiod on bud burst. Twigs with leaf buds were collected in winter (February 2020) and maintained in four conditions: 1) long day length (16L8D; LD), 2) short day length (8L16D; SD), 3) day interruption for 2-h in the middle of the 16-h light period and a 6-h dark period (DI; total time of light period is the same as LD), and 4) night interruption with 2-h of light in the middle of the dark period and a 6-h light period (NI; total time of light period is the same as SD) for a duration of 40 d. We then measured the number of days until burst for each bud. Timing of bud burst was delayed in the SD treatment compared to the LD, DI, and NI treatments. These results demonstrate that the difference in bud burst phenology observed between SD and LD conditions is mainly due to day length perception rather than DLI, and an uninterrupted night period plays a major role in the perception of photoperiod. Our results provide the experimental evidence of perception of photoperiod regulating bud burst in spring.

Champions of winter survival: cold acclimation and molecular regulation of cold hardiness in evergreen conifers.

Evergreen conifers are champions of winter survival, based on their remarkable ability to acclimate to cold and develop cold hardiness. Counterintuitively, autumn cold acclimation is triggered not only by exposure to low temperature, but also by a combination of decreasing temperature, decreasing photoperiod and changes in light quality. These environmental cues control a network of signaling pathways that coordinate cold acclimation and cold hardiness in overwintering conifers, leading to cessation of growth, bud dormancy, freezing tolerance and changes in energy metabolism. Advances in genomic, transcriptomic and metabolomic tools for conifers have improved our understanding of how trees sense and respond to changes in temperature and light during cold acclimation and the development of cold hardiness, but there remain considerable gaps deserving further research in conifers. In the first section of this review, we focus on the physiological mechanisms used by evergreen conifers to adjust metabolism seasonally and to protect overwintering tissues against winter stresses. In the second section, we review how perception of low temperature and photoperiod regulate the induction of cold acclimation. Finally, we explore the evolutionary context of cold acclimation in conifers and evaluate challenges imposed on them by changing climate and discuss emerging areas of research in the field.

Transcriptomic analysis of flower induction for long-day pitaya by supplementary lighting in short-day winter season

BackgroundPitayas are currently attracting considerable interest as a tropical fruit with numerous health benefits. However, as a long-day plant, pitaya plants cannot flower in the winter season from November to April in Hainan, China. To harvest pitayas with high economic value in the winter season, it is necessary to provide supplementary lighting at night to induce flowering. To further explore the molecular regulating mechanisms of flower induction in pitaya plants exposed to supplementary lighting, we used de novo RNA sequencing-based transcriptomic analysis for four stages of pitaya plants subjected to light induction.ResultsWe assembled 68,113 unigenes in total, comprising 29,782 unigenes with functional annotations in the NR database, 20,716 annotations in SwissProt, 18,088 annotations in KOG, and 11,059 annotations in KEGG. Comparisons between different samples revealed different numbers of significantly differentially expressed genes (DEGs). A number of DEGs involved in energy metabolism-related processes and plant hormone signaling were detected. Moreover, we identified many CONSTANS-LIKE, FLOWERING LOCUS T, and other DEGs involved in the direct regulation of flowering including CDF and TCP, which function as typical transcription factor genes in the flowering process. At the transcriptomic level, we verified 13 DEGs with different functions in the time-course response to light-induced flowering by quantitative reverse-transcription PCR analysis.ConclusionsThe identified DEGs may include some key genes controlling the pitaya floral-induction network, the flower induction and development is very complicated, and it involves photoperiod perception and different phytohormone signaling. These findings will increase our understanding to the molecular mechanism of floral regulation of long-day pitaya plants in short-day winter season induced by supplementary lighting.

Branching Regulator BRC1 Mediates Photoperiodic Control of Seasonal Growth in Hybrid Aspen

Cessation of growth as winter approaches is a key adaptive trait for survival of perennial plants, such as long-lived trees native to boreal and temperate regions [1, 2]. The timing of growth cessation in these plants is controlled by photoperiodic cues. As shown recently, perception of growth-repressive short photoperiod (SP) mediated via components of circadian clock results indownregulation of the tree ortholog of Arabidopsis flowering regulator FLOWERING LOCUS T(FT), FT2[3, 4]. Downregulation of FT2 results in suppression of downstream components LAP1 (orthologousto the Arabidopsis floral meristem identity gene APETALA1) and AIL1 (orthologous to AINTEGUMENTA in Arabidopsis), culminating in induction of growth cessation and bud set [5-7]. Results presented here reveal that, in addition to the CO/FT pathway, a photoperiodically controlled negative feedback loop involving a tree ortholog of Arabidopsis BRANCHED1 (BRC1) (a member of TEOSINTE BRANCHED 1, CYCLOIDEA, PCF family), LAP1, and FT2 participates in regulation of seasonal growth in the model tree hybrid aspen. In growth-promotive long photoperiod, LAP1 suppresses expression of BRC1, but upon perception of growth-repressive SP, downregulation of LAP1 de-represses expression of its downstream target BRC1. BRC1 physically interacts with FT2, and BRC1-FT interaction further reinforces the effect of SP and triggers growth cessation by antagonizing FT action. Accordingly, BRC1 gain and loss of function result in early and retarded growth cessation responses to SP, respectively. Thus, these results reveal a regulatory feedback loop that reinforces responses to SP and induction of seasonal growth cessation.

Manipulation of photoperiod perception advances gonadal growth but not laying date in the great tit

In seasonal environments, organisms use biotic and abiotic cues to time various biological processes that are crucial for growth, survival and reproductive success. Photoperiod is the best‐known cue used to regulate gonadal development, migration and moult of many animal species. In birds, the relationship between photoperiod and gonadal development is clearly established, but we have little understanding on whether photoperiod also regulates actual timing of egg laying under natural conditions. Elucidating the link between photoperiod and timing of breeding is however key to understand whether an evolutionary change in sensitivity to photoperiod is a possible mechanism through which organisms could adjust their seasonal timing in response to climate warming. Here, we investigated the causal relationship between photoperiod, gonadal growth and laying date in wild female great tits. We experimentally increased the photoperiod perceived by the birds in spring by clipping head feathers, and we subsequently monitored gonadal development in the lab and egg laying dates in the wild. We show that our manipulation increased the photoperiod perceived by the birds to a level that approximately corresponds to an advancement of ten calendar days. This increase in perceived photoperiod led to an acceleration of gonadal development, but not to an advancement of egg laying dates. Our results indicate that photoperiod sensitivity is not constraining the advancement of laying date under current environmental conditions and suggest that evolution of sensitivity to other supplementary cues is necessary to advance reproduction under global warming.

LHY2 Integrates Night-Length Information to Determine Timing of Poplar Photoperiodic Growth

Day length is a key indicator of seasonal information that determines major patterns of behavior in plants and animals. Photoperiodism has been described in plants for about 100 years, but the underlying molecular mechanisms of day length perception and signal transduction in many systems are not well understood. In trees, photoperiod perception plays a major role in growth cessation during the autumn as well as activating the resumption of shoot growth in the spring, both processes controlled by FLOWERING LOCUS T2 (FT2) expression levels and critical for the survival of perennial plants over winter [1-4]. It has been shown that the conserved role of poplar orthologs to Arabidopsis CONSTANS (CO) directly activates FT2 expression [1, 5]. Overexpression of poplar CO is, however, not sufficient to sustain FT2 expression under short days [5], pointing to the presence of an additional short-day-dependent FT2 repression pathway in poplar. We find that night length information is transmitted via the expression level of a poplar clock gene, LATE ELONGATED HYPOCOTYL 2 (LHY2), which controls FT2 expression. Repression of FT2 is a function of the night extension and LHY2 expression level. We show that LHY2 is necessary and sufficient to activate night length repressive signaling. We propose that the photoperiodic control of shoot growth in poplar involves a balance between FT2 activating and repressing pathways. Our results show that poplar relies on night length measurement to determine photoperiodism through interaction between light signaling pathways and the circadian clock.

Expression of sugarcane genes associated with perception of photoperiod and floral induction reveals cycling over a 24-hour period.

The genetic network resulting in the production of an inflorescence is complex, involving one or more pathways including the photoperiod, maturity, gibberellin and autonomous pathways, and induction and repression of genes along the pathways. Understanding the cyclic expression profile of genes involved with photoperiod perception and floral pathway induction in sugarcane, an intermediate-short day plant (ISD), is crucial for identifying key genes and understanding how the profile changes in response to floral induction signals under decreasing daylengths. Homologues of 21 genes, and some gene alleles, associated with photoperiod perception and the flower induction pathway were examined in sugarcane variety Q174 over a 24-h light-dark cycle. The strongest expression of these genes was seen in the immature spindle leaves and levels of expression generally decreased with increasing leaf age. Significant changes in gene expression levels during a 24-h cycle were observed for 16 of the 21 genes tested. We have now defined an important baseline for expression patterns over a 24-h cycle in non-inductive conditions in sugarcane. These results can be utilised to select the optimal time for detecting changes during floral induction, differences between varieties that are responsive/non-responsive to photoperiod induction, and to identify genes that may be manipulated to enhance or inhibit flowering.

Photoperiodism dynamics during the domestication and improvement of soybean.

Soybean (Glycine max) is a facultative short-day plant with a sensitive photoperiod perception and reaction system, which allows it to adjust its physiological state and gene regulatory networks to seasonal and diurnal changes in environmental conditions. In the past few decades, soybean cultivation has spread from East Asia to areas throughout the world. Biologists and breeders must now confront the challenge of understanding the molecular mechanism of soybean photoperiodism and improving agronomic traits to enable this important crop to adapt to geographical and environmental changes. In this review, we summarize the genetic regulatory network underlying photoperiodic responses in soybean. Genomic and genetic studies have revealed that the circadian clock, in conjunction with the light perception pathways, regulates photoperiodic flowering. Here, we provide an annotated list of 844 candidate flowering genes in soybean, with their putative biological functions. Many photoperiod-related genes have been intensively selected during domestication and crop improvement. Finally, we describe recent progress in engineering photoperiod-responsive genes for improving agronomic traits to enhance geographic adaptation in soybean, as well as future prospects for research on soybean photoperiodic responses.

Identification of fasciclin-like arabinogalactan proteins in textile hemp (Cannabis sativa L.): in silico analyses and gene expression patterns in different tissues

BackgroundThe fasciclin-like arabinogalactan proteins (FLAs) belong to the arabinogalactan protein (AGP) superfamily and are known to play different physiological roles in plants. This class of proteins was shown to participate in plant growth, development, defense against abiotic stresses and, notably, cell wall biosynthesis. Although some studies are available on the characterization of FLA genes from different species, both woody and herbaceous, no detailed information is available on the FLA family of textile hemp (Cannabis sativa L.), an economically important fibre crop.ResultsBy searching the Cannabis genome and EST databases, 23 CsaFLAs have been here identified which are divided into four phylogenetic groups. A real-time qPCR analysis performed on stem tissues (isolated bast fibres and shivs sampled at three heights), hypocotyls (6-9-12-15-17-20 days-old), whole seedlings, roots, leaves and female/male flowers of the monoecious fibre variety Santhica 27, indicates that the identified FLA genes are differentially expressed. Interestingly, some hemp FLAs are expressed during early phases of fibre growth (elongation), while others are more expressed in the middle and base of the stem and thus potentially involved in secondary cell wall formation (fibre thickening). The bioinformatic analysis of the promoter regions shows that the FLAs upregulated in the younger regions of the stem share a conserved motif related to flowering control and regulation of photoperiod perception. The promoters of the FLA genes expressed at higher levels in the older stem regions, instead, share a motif putatively recognized by MYB3, a transcriptional repressor belonging to the MYB family subgroup S4.ConclusionsThese results point to the existence of a transcriptional network fine-tuning the expression of FLA genes in the older and younger regions of the stem, as well as in the bast fibres/shivs of textile hemp. In summary, our study paves the way for future analyses on the biological functions of FLAs in an industrially relevant fibre crop.

Artificially extended photoperiod administered to pre-partum mares via blue light to a single eye: Observations on gestation length, foal birth weight and foal hair coat at birth

In seasonally breeding animals, photoperiod perception is crucial for timing of important physiological events. In the horse, long day photoperiod influences the onset of ovulation and cyclicity, shedding of the heavier winter coat and the timing of parturition. In this compilation of studies, conducted across three breeding seasons and two countries, the impact of artificially extended day length was investigated on gestation length, foal birth weight and foal hair coat at birth. The light therapy was administered to pre-partum mares via mobile head worn masks which provided short wavelength blue light to a single eye. In Study 1, reductions in gestation lengths were observed following administration of artificially extended day length (124.8 ± 15.11 days) in the final months of pregnancy to a group of Thoroughbred mares compared to controls (P < 0.05; 339.7 ± 9.56 days vs 350.6 ± 9.13). Study 2 revealed that pre-partum exposure to artificially extended day length (104.6 ± 9.89 days) increased foal birth weight compared to controls (47.13 ± 2.93 kg vs 43.51 ± 6.14 kg; P < 0.05) in mares bred early in the year. In Study 3, artificially extended day length (87.53 ± 19.6 days) administered to pre-partum mares affected the coat condition of foals at birth with respect to hair weight (P < 0.0001) and hair length (P < 0.0001) compared to controls (0.34 ± 0.20 μg vs 0.59 ± 0.12 μg and 1.93 ± 0.56 cm vs 2.56 ± 0.32 cm, respectively). Collectively, these studies serve to highlight the influential role of the circa-annual changes in photoperiod length on the pre-partum mare for normal foetal development during the natural breeding season. It also emphasizes the potential that exists to improve breeding efficiency parameters by artificially simulating this important environmental cue in the latter stages of gestation against the backdrop of an economically driven early breeding season.

Phenological response of spring wheat to timing of photoperiod perception: The effect of sowing depth on final leaf number in spring wheat

Wheat phenological modelling literature suggests final leaf number (FLN) targets of wheat (Triticum aestivum) will be set only once daylight is perceived and will be based upon environmental and cultivar-specific genetics at that time. Development is thought to proceed relative to thermal time regardless of light perception prior to emergence. Modelled predictions of final leaf number (FLN) and thence anthesis are based on this mechanism. Results did not support this hypothesis, and we suggest and alternative hypothesis based on molecular interactions between vernalization genes Vrn1, Vrn2 and Vrn3.

The clock gene period is essential for the photoperiodic response in the jewel wasp Nasonia vitripennis (Hymenoptera: Pteromalidae)

The role of the clock gene period (per) in photoperiodism was investigated in the jewel wasp Nasonia vitripennis (Walker) (Hymenoptera: Pteromalidae). Typically, females reared under long days lay eggs that develop to adulthood without developmental interruption, whereas those reared under short days lay eggs that enter larval diapause. We found that RNA interference (RNAi) of per disrupts the photoperiodic response; RNAi wasps failed to produce diapause-destined eggs in response to short days. This indicates that per is essential for the photoperiodic response in this species. Exposure to low temperature swiftly affects maternal physiology and prompts N. vitripennis females to lay diapause-destined eggs. Interestingly, per RNAi females also laid diapause-destined eggs in response to the low temperature treatment in the current study. This finding indicates that per RNAi did not disrupt the maternal physiology that was directly involved in production of diapause-destined eggs, but it did affect photoperiodic perception. We also investigated the expression patterns of several clock genes, per, mammalian-type cryptochrome (cry-m), cycle (cyc), PAR-domain protein 1 (Pdp1), and clockwork orange (cwo), to determine whether their expression patterns were affected by different photoperiods.

DhEFL2, 3 and 4, the three EARLY FLOWERING4-like genes in a Doritaenopsis hybrid regulate floral transition.

DhEFL2, 3 and 4 regulate the flowering of Doritaenopsis . These genes could rescue elf4-1 phenotype in Arabidopsis while its overexpression delayed flowering. Phalaenopsis are popular floral plants, and studies on orchid flowering genes could help develop off-season cultivars. Early flowering 4 (ELF4) of A. thaliana has been shown to be involved in photoperiod perception and circadian regulation. We isolated two members of the ELF4 family from Doritaenopsis hybrid (Doritaenopsis 'Tinny Tender' (Doritaenopsis Happy Smile × Happy Valentine)), namely, DhEFL2 and DhEFL3 (DhEFL4 has been previously cloned). Multiple alignment analysis of the deduced amino acid sequences of the three DhEFL homologs showed that DhEFL4 and DhEFL2 are similar with 72% identical amino acids, whereas DhEFL3 is divergent with 72% similarity with DhEFL2 and 68% similarity with DhEFL4. DhEFL3 forms a separate phylogenetic subgroup and is far away from DhEFL2 and DhEFL4. The diurnal expression patterns of DhEFL2, 3, and 4 are similar in the long-day photoperiod conditions; however, in the short-day conditions, DhEFL3 is different from DhEFL2 and 4. For the DhEFL2, 3, and 4 genes, the strongest audience expression organs are the stem, petal and bud, respectively. The ectopic expression of DhEFL2, 3, or 4 in transgenic A. thaliana plants (Ws-2 ecotype) showed novel phenotypes by late flowering and more rosette leaves. The ectopic expression of DhEFL2, 3, or 4 could complement the elf4-1 flowering time and hypocotyl length defects in transgenic A. thaliana elf4-1 mutant plants. These results strongly suggest that DhEFL2, 3, and 4 may be involved in regulation of flower formation and floral induction in Doritaenopsis.

Overexpression of Doritaenopsis Hybrid EARLY FLOWERING 4-like4 Gene, DhEFL4, Postpones Flowering in Transgenic Arabidopsis

The EARLY FLOWERING 4 (ELF4) gene has been reported as a requirement for photoperiod perception and circadian function. In this study, an ELF4 homolog gene EARLY FLOWERING 4-like4 (EFL4) was isolated from Doritaenopsis “Tinny Tender” (Doritaenopsis Happy Smile × Happy Valentine) and designated as DhEFL4. The acquired DhEFL4 cDNA was 593 bp with a 345 bp open reading frame encoding 114 amino acids. The putative DhEFL4 protein contained a conserved region, DUF1313, which is shared by the ELF4 family. Amino acid sequence alignment showed that DhEFL4 shared high similarity to ELF4 and ELF4-like homologs from other species. The DhEFL4 promoter was also obtained, and 241 cis-elements were found. The diurnal expression of DhEFL4, which may be affected by the EVENINGAT (EE) and circadian motif was analyzed by quantitative PCR under short- and long-day conditions. Reverse-transcription PCR analysis results showed that DhEFL4 is an evening-expressed circadian gene. DhEFL4 was expressed in both vegetative and reproductive organs, and its transcripts reached higher levels in the buds. To further study the function of the DhEFL4 gene, DhEFL4 was overexpressed in Arabidopsis thaliana by Agrobacterium-mediated transformation. The flowering of these transgenic plants was more delayed than that of wild-type Arabidopsis by 12−14 days, and flower stems increased. Results indicated that DhEFL4 may perform an important function in the regulation of flowering.

Perception of photoperiod in individual buds of mature trees regulates leaf-out.

Experimental data on the perception of day length and temperature in dormant temperate zone trees are surprisingly scarce. In order to investigate when and where these environmental signals are perceived, we carried out bagging experiments in which buds on branches of Fagus sylvatica, Aesculus hippocastanum and Picea abies trees were exposed to natural light increase or kept at constant 8-h days from December until June. Parallel experiments used twigs cut from the same trees, harvesting treated and control twigs seven times and then exposing them to 8- or 16-h days in a glasshouse. Under 8-h days, budburst in Fagus outdoors was delayed by 41 d and in Aesculus by 4 d; in Picea, day length had no effect. Buds on nearby branches reacted autonomously, and leaf primordia only reacted to light cues in late dormancy after accumulating warm days. Experiments applying different wavelength spectra and high-resolution spectrometry to buds indicate a phytochrome-mediated photoperiod control. By demonstrating local photoperiodic control of buds, revealing the time when these signals are perceived, and showing the interplay between photoperiod and chilling, this study contributes to improved modelling of the impact of climate warming on photosensitive species.