Photoperiodic Cues Research Articles

Species that require long day conditions to flower are not advancing their flowering phenology as fast as species without photoperiod requirements.

Over the last few decades, many plant species have shown changes in phenology, such as the date on which they germinate, bud or flower. However, some species are changing slower than others, potentially due to daylength (photoperiod) requirements. We combined data on flowering time advancement with published records of photoperiod sensitivity to try to predict which species are advancing their flowering time. Data availability limited us to the Northern Hemisphere. Cross-species analyses showed that short day plants advanced their flowering time by 1.4 days per decade, day neutral plants advanced by 0.9 days per decade, but long day plants delayed their flowering by 0.2 days per decade. However, photoperiod sensitivity status was moderately phylogenetically conserved, and the differences in flowering time advancement were not significant after phylogeny was accounted for. Both annual and perennial herbs were more likely to have long day photoperiod cues than woody species, which were instead more likely to have short day photoperiod cues. Short day plants are keeping up with plants that do not have photoperiod requirements, suggesting that daylength requirements do not hinder changes in phenology. However, long day plants are not changing their phenology and may risk falling behind as competitors and pollinators adapt to climate change.

Removal of Exogenous Stimuli Reveals a Canalization of Circadian Physiology in a Vertically Migrating Copepod.

Diel rhythms are observed across taxa and are important for maintaining synchrony between the environment and organismal physiology. A striking example of this is the diel vertical migration undertaken by zooplankton, some of which, such as the 5 mm-long copepod Pleuromamma xiphias (P. xiphias), migrate hundreds of meters daily between the surface ocean and deeper waters. Some of the molecular pathways that underlie the expressed phenotype at different stages of this migration are entrained by environmental variables (e.g., day length and food availability), while others are regulated by internal clocks. We identified a series of proteomic biomarkers that vary across ocean DVM and applied them to copepods incubated in 24 h of darkness to assess circadian control. The dark-incubated copepods shared some proteomic similarities to the ocean-caught copepods (i.e., increased abundance of carbohydrate metabolism proteins at night). Shipboard-incubated copepods demonstrated a clearer distinction between night and day proteomic profiles, and more proteins were differentially abundant than in the in situ copepods, even in the absence of the photoperiod and other environmental cues. This pattern suggests that there is a canalization of rhythmic diel physiology in P. xiphias that reflects likely circadian clock control over diverse molecular pathways.

Decoding the effect of photoperiodic cues in transducing kisspeptin-melatonin circuit during the pubertal onset in common carp.

This study unravels the intricate interplay between photoperiod, melatonin, and kisspeptin to orchestrate the pubertal onset of Common carp. Female fingerlings exposed to long days (LD) exhibited a hormonal crescendo, with upregulated hypothalamic-pituitary-ovarian (HPO) axis genes (kiss1, kiss1r, kiss2, gnrh2, gnrh3) and their downstream targets (lhr, fshr, ar1, esr1). However, the expression of the melatonin receptor (mtnr1a) diminished in LD, suggesting a potential inhibitory role. This hormonal symphony was further amplified by increased activity of key transcriptional regulators (gata1, gata2, cdx1, sp1, n-myc, hoxc8, plc, tac3, tacr3) and decreased expression of delayed puberty genes (mkrn1, dlk1). In contrast, short days (SD) muted this hormonal chorus, with decreased gnrh gene and regulator expression, elevated mtnr1a, and suppressed gonadal development. In in-vitro, estradiol mimicked the LD effect, boosting gnrh and regulator genes while dampening mtnr1a and melatonin-responsive genes. Conversely, melatonin acted as a conductor, downregulating gnrh and regulator genes and amplifying mtnr1a. Our findings illuminate the crucial roles of melatonin and kisspeptin as opposing forces in regulating pubertal timing. LD-induced melatonin suppression allows the kisspeptin symphony to flourish, triggering GnRH release and, ultimately, gonadal maturation. This delicate dance between photoperiod, melatonin, and kisspeptin orchestrates common carp's transition from juvenile to reproductive life.

Transcriptomic basis of sex loss in the pea aphid

BackgroundTransitions from sexual to asexual reproduction are common in eukaryotes, but the underlying mechanisms remain poorly known. The pea aphid—Acyrthosiphon pisum—exhibits reproductive polymorphism, with cyclical parthenogenetic and obligate parthenogenetic lineages, offering an opportunity to decipher the genetic basis of sex loss. Previous work on this species identified a single 840 kb region controlling reproductive polymorphism and carrying 32 genes. With the aim of identifying the gene(s) responsible for sex loss and the resulting consequences on the genetic programs controlling sexual or asexual embryogenesis, we compared the transcriptomic response to photoperiod shortening—the main sex-inducing cue—of a sexual and an obligate asexual lineage of the pea aphid, focusing on heads (where the photoperiodic cue is detected) and embryos (the final target of the cue).ResultsOur analyses revealed that four genes (one expressed in the head, and three in the embryos) of the region responded differently to photoperiod in the two lineages. We also found that the downstream genetic programs expressed during embryonic development of a future sexual female encompass ∼1600 genes, among which miRNAs, piRNAs and histone modification pathways are overrepresented. These genes mainly co-localize in two genomic regions enriched in transposable elements (TEs).ConclusionsOur results suggest that the causal polymorphism(s) in the 840 kb region somehow impair downstream epigenetic and post-transcriptional regulations in obligate asexual lineages, thereby sustaining asexual reproduction.

Food and social cues modulate reproductive development but not migratory behavior in a nomadic songbird, the Pine Siskin

Abstract Many animals rely on photoperiodic and non-photoperiodic environmental cues to gather information and appropriately time life-history stages across the annual cycle, such as reproduction, molt, and migration. Here, we experimentally demonstrate that the reproductive physiology, but not migratory behavior, of captive Pine Siskins (Spinus pinus) responds to both food and social cues during the spring migratory-breeding period. Pine Siskins are a nomadic finch with a highly flexible breeding schedule and, in the spring, free-living Pine Siskins can wander large geographic areas and opportunistically breed. To understand the importance of non-photoperiodic cues to the migratory-breeding transition, we maintained individually housed birds on either a standard or enriched diet in the presence of group-housed heterospecifics or conspecifics experiencing either the standard or enriched diet type. We measured body condition and reproductive development of all Pine Siskins and, among individually housed Pine Siskins, quantified nocturnal migratory restlessness. In group-housed birds, the enriched diet caused increases in body condition and, among females, promoted reproductive development. Among individually housed birds, female reproductive development differed between treatment groups, whereas male reproductive development did not. Specifically, individually housed females showed greater reproductive development when presented with conspecifics compared to heterospecifics. The highest rate of female reproductive development, however, was observed among individually housed females provided the enriched diet and maintained with group-housed conspecifics on an enriched diet. Changes in nocturnal migratory restlessness did not vary by treatment group or sex. By manipulating both the physical and social environment, this study demonstrates how multiple environmental cues can affect the timing of transitions between life-history stages with differential responses between sexes and between migratory and reproductive systems.

Experimental designs for testing the interactive effects of temperature and light in ecology: The problem of periodicity

AbstractTemperature and light cues interact to control many biological processes. Experiments give researchers the ability to manipulate these environmental cues independently and can be designed to robustly quantify their individual and interactive effects on any particular biological activity. Such experiments have produced important insights into the environmental controls on numerous biological processes in both plant and animal taxa across terrestrial and aquatic environments. Testing the interactive effects of multiple environmental cues, however, requires experimental treatments to be fully independent; any unmeasured experimental covariation among treatments can result in incorrect conclusions.Using a database of controlled environment experiments on the spring phenology of woody plants as a case study, we highlight how a common experimental set‐up, designed to parse the interactive effects of temperature and photoperiod on time to budburst, introduces a latent experimental covariation of these treatments by coupling photo‐ and thermoperiodicity. Using data simulations, algebraic corrections and a comparative analysis of published experiments, we demonstrate how this unmeasured experimental covariation biases statistical inference regarding the relative contribution of light and temperature cues to phenological variation.We identify this experimental covariation in more than 40% of published phenology studies that manipulate photoperiod. Our analyses demonstrate that the coupling of thermo‐ and photoperiodicity results in the overestimation of the effect of photoperiod, the underestimation of forcing effects, and misleading conclusions about their interactions on phenology. This may, in part, explain why the significance of photoperiod cues for spring phenology is currently debated in the literature.Accurate forecasting of how varying environmental conditions will impact the dynamics of biological events requires accurately quantifying cue responses. To this end, we present several options for statistical corrections and alternative experimental designs that can provide more robust estimates of the relative effects of temperature and photoperiod on phenology and many other biological processes controlled by temperature and light.Read the freePlain Language Summaryfor this article on the Journal blog.

Cross‐disciplinary insights into the mechanisms of plant cold hardiness: From molecules to ecosystems

Cross‐disciplinary insights into the mechanisms of plant cold hardiness: From molecules to ecosystems

Exposure to artificial light at night mediates the locomotion activity and oviposition capacity of Dastarcus helophoroides (Fairmaire).

Light entrains the endogenous circadian clocks of organisms to synchronize their behavioral and physiological rhythms with the natural photoperiod. The presence of artificial light at night disrupts these photoperiodic cues and is currently considered to be a major threat to key fitness-related behaviors, including sleep disruption and physiological stress. Research on the ecological influence of forest pest and their natural enemies is lacking. The wood-boring insects significantly damage forest and urban forest ecosystem functions. The parasitic beetles, Dastarcus helophoroides is an important natural enemy of wood-boring insects, especially those in the Cerambycidae family. However, the effect of artificial light at night on the locomotor rhythms and oviposition capacity of D. helophoroides has received little attention. To address this gap, diel changes in the locomotor activity and number of eggs laid by female D. helophoroides was analyzed under different light-dark (LD) cycles and temperatures. The results showed that the 24-h rhythmic of locomotor activity in these beetles was elevated in darkness and reduced under illumination, indicating that they are nocturnal insects. This activity has two major peaks, the evening (1-8h after lights off) and morning (3.5-12.5h after lights off) components, reflecting that light mediate regular changes in locomotor activity. Moreover, the circadian rhythms and active percentage were influenced by the illumination duration and temperature, especially constant light and 40°C. Females laid more eggs under the 16L: 8 D cycles at 30°C than under the other combinations of photoperiod (including constant light and darkness) and temperature. Finally, the potential influence of exposure to four ecologically relevant intensities of artificial light at night (0, 1, 10 or 100 lx) on oviposition capacity was studied. The results showed that lifetime exposure to bright artificial light (1-100 lx) at night decreased the number of eggs laid relative to those laid with no lighting at night. These results demonstrate that chronic exposure to bright artificial light at night may influence the locomotor activity and oviposition capacity of this parasitic beetle.

Flowering responses of serradella (Ornithopus spp.) and subterranean clover (Trifolium subterraneum L.) to vernalisation and photoperiod and their role in maturity type determination and flowering date stability

Context Serradellas (Ornithopus spp.) are promising alternative annual legumes to subterranean clover (Trifolium subterraneum L.), for permanent, temperate pastures. However, many cultivars exhibit unstable flowering dates across years. This is a risk for seed production and persistence. Aim This study assessed how vernalisation and photoperiod cues determine maturity type and flowering date stability among serradella cultivars. Methods First flower appearance was recorded for early and late maturing cultivars of yellow serradella (Ornithopus compressus L.), French serradella (Ornithopus sativus Brot.) and subterranean clover after exposure to six vernalisation treatments (0, 1, 3, 5, 7 or 9 weeks at 5°C) with subsequent growth under four photoperiods (8, 12, 16 or 20 h). Key results ‘Intrinsic earliness’ differed by only zero to three nodes for cultivars within species, indicating that maturity type was determined primarily by a cultivar’s responses to vernalisation and photoperiod. An interaction between these responses was observed, with a precipitous decline in the requirement for vernalisation when photoperiods exceeded 12 h. Many cultivars also displayed a persistent component to their vernalisation response, whereby long photoperiods (20 h) did not completely negate the response to vernalisation. Conclusions Later maturity was associated particularly with need for long exposure to the vernalisation treatment to minimise the duration from sowing to first flower appearance. Stable flowering is more likely when a cultivar has components of its vernalisation requirement that are not satisfied before autumn ends to prevent premature flowering, and a photoperiod response in spring that overrides any unmet vernalisation requirement. Implications Persistence by serradella cultivars requires selection for suitable responsiveness to vernalisation and photoperiod.

Cold acclimation threshold induction temperatures of switchgrass ecotypes grown under a long and short photoperiod

Plants can cold acclimate to enhance their freezing tolerance by sensing declining temperature and photoperiod cues. However, the factors influencing genotypic variation in the induction of cold acclimation are poorly understood among perennial grasses. We hypothesized that the more northern upland switchgrass (Panicum virgatum L.) ecotype develops a higher degree of freezing tolerance by initiating cold acclimation at higher temperatures as compared with the coastal and southern lowland ecotypes. First, we determined the optimal method for assessing freezing tolerance and the length of exposure to 8/4°C required to induce the maximum level of freezing tolerance in the most northern upland and most southern lowland genotypes. We characterized the maximum freezing tolerance of eight uplands, three coastal and five lowland genotypes grown for 21 days at 8/4°C and a 10 or 16 h photoperiod. Next, we identified the temperature required to induce cold acclimation by exposing the 16 genotypes for 7 days at 20-6°C constant temperatures under a 10 or 16 h photoperiod. Cold acclimation initiated at temperatures 5 and 7°C higher in upland than in coastal and lowland genotypes. Among upland genotypes the shorter photoperiod induced cold acclimation at a 1°C higher temperature. Genotypes originating from a more northern latitude initiate cold acclimation at higher temperatures and develop higher maximum freezing tolerances. An earlier response to declining temperatures may provide the upland ecotype with additional time to prepare for winter and provide an advantage when plants are subjected to the rapid changes in fall temperature associated with injurious frosts.

Impact of food restriction on the medio-basal hypothalamus of intact ewes as revealed by a large-scale transcriptomics study.

In mammals, the medio-basal hypothalamus (MBH) integrates photoperiodic and food-related cues to ensure timely phasing of physiological functions, including seasonal reproduction. The current human epidemics of obesity and associated reproductive disorders exemplifies the tight link between metabolism and reproduction. Yet, how food-related cues impact breeding at the level of the MBH remains unclear. In this respect, the sheep, which is a large diurnal mammal with a marked dual photoperiodic/metabolic control of seasonal breeding, is a relevant model. Here, we present a large-scale study in ewes (n=120), which investigated the impact of food restriction (FRes) on the MBH transcriptome using unbiased RNAseq, followed by RT-qPCR. Few genes (~100) were impacted by FRes and the transcriptional impact was very modest (<2-fold increase or < 50% decrease for most genes). As anticipated, FRes increased expression of Npy/AgRP/LepR and decreased expression of Pomc/Cartpt, while Kiss1 expression was not impacted. Of particular interest, Eya3, Nmu and Dio2, genes involved in photoperiodic decoding within the MBH, were also affected by FRes. Finally, we also identified a handful of genes not known to be regulated by food-related cues (e.g., RNase6, HspA6, Arrdc2). In conclusion, our transcriptomics study provides insights into the impact of metabolism on the MBH in sheep, which may be relevant to human, and identifies possible molecular links between metabolism and (seasonal) reproduction.

Plasticity in Photoperiodism: Drosophila montana Females Have a Life-Long Ability to Switch From Reproduction to Diapause.

Photoperiodic reproductive diapause is an essential part of female life cycle in several insect species living on high latitudes, where overwintering in reproductive stage involves high risks for survival and progeny production. The sensitive period (SP), during which photoperiodic cues can trigger the switch from direct development to diapause, can last from a few hours or days after emergence to the entire life span of females. Moreover, in some species, sexually mature females can enter post-reproductive diapause as a response to decreasing day length and/or temperature. We studied the duration of SP for diapause induction and the females' ability to enter post-reproductive diapause at short day lengths in Drosophila montana strains from different latitudes in Europe, North America, and Japan. Our study shows that the females of this species have a life-long SP and that they retain an ability to switch between reproduction and diapause as a response to back-and-forth changes in day length for at least 3 months. D. montana strains from different latitudes showed high variation in females' ability to enter post-reproductive diapause; females of the southern strains generally requiring longer time and/or lower temperature to enter this stage than those of the northern strains. Moreover, the proportion of females that switched to post-reproductive diapause in 3 weeks in short day conditions at 16 °C showed positive correlation with the critical day length (CDL) for diapause induction and the latitudinal and continental origin of the strains. Life-long SP increases females' flexibility to respond to short-term changes in environmental conditions and enables reproducing females to switch to post-reproductive diapause when the days get shorter and colder toward the autumn. This ability can play a major role in species phenology and should be taken into account in theoretical and empirical studies on insect adaptation to seasonal variation.

Diel Rhythm and Thermal Independence of Metabolic Rate in a Benthic Shark.

Biological rhythms that are mediated by exogenous factors, such as light and temperature, drive the physiology of organisms and affect processes ranging from cellular to population levels. For elasmobranchs (i.e. sharks, rays, and skates), studies documenting diel activity and movement patterns indicate that many species are crepuscular or nocturnal in nature. However, few studies have investigated the rhythmicity of elasmobranch physiology to understand the mechanisms underpinning these distinct patterns. Here, we assess diel patterns of metabolic rates in a small meso-predator, the epaulette shark (Hemiscyllium ocellatum), across ecologically relevant temperatures and upon acutely removing photoperiod cues. This species possibly demonstrates behavioral sleep during daytime hours, which is supported herein by low metabolic rates during the day and a 1.7-fold increase in metabolic rates at night. From spring to summer seasons, where average average water temperature temperatures for this species range 24.5 to 28.5 °C, time of day, and not temperature, had the strongest influence on metabolic rate. These results indicate that this species, and perhaps other similar species from tropical and coastal environments, may have physiological mechanisms in place to maintain metabolic rate on a seasonal time scale regardless of temperature fluctuations that are relevant to their native habitats.

2b-RAD Genotyping of the Seagrass Cymodocea nodosa Along a Latitudinal Cline Identifies Candidate Genes for Environmental Adaptation.

Plant populations distributed along broad latitudinal gradients often show patterns of clinal variation in genotype and phenotype. Differences in photoperiod and temperature cues across latitudes influence major phenological events, such as timing of flowering or seed dormancy. Here, we used an array of 4,941 SNPs derived from 2b-RAD genotyping to characterize population differentiation and levels of genetic and genotypic diversity of three populations of the seagrass Cymodocea nodosa along a latitudinal gradient extending across the Atlantic-Mediterranean boundary (i.e., Gran Canaria—Canary Islands, Faro—Portugal, and Ebro Delta—Spain). Our main goal was to search for potential outlier loci that could underlie adaptive differentiation of populations across the latitudinal distribution of the species. We hypothesized that such polymorphisms could be related to variation in photoperiod-temperature regime occurring across latitudes. The three populations were clearly differentiated and exhibited diverse levels of clonality and genetic diversity. Cymodocea nodosa from the Mediterranean displayed the highest genotypic richness, while the Portuguese population had the highest clonality values. Gran Canaria exhibited the lowest genetic diversity (as observed heterozygosity). Nine SNPs were reliably identified as outliers across the three sites by two different methods (i.e., BayeScan and pcadapt), and three SNPs could be associated to specific protein-coding genes by screening available C. nodosa transcriptomes. Two SNPs-carrying contigs encoded for transcription factors, while the other one encoded for an enzyme specifically involved in the regulation of flowering time, namely Lysine-specific histone demethylase 1 homolog 2. When analyzing biological processes enriched within the whole dataset of outlier SNPs identified by at least one method, “regulation of transcription” and “signalling” were among the most represented. Our results highlight the fundamental importance signal integration and gene-regulatory networks, as well as epigenetic regulation via DNA (de)methylation, could have for enabling adaptation of seagrass populations along environmental gradients.

Photoperiodic regulation of avian physiology: From external coincidence to seasonal reproduction.

Seasonal cycles of environmental cues generate variation in the timing of life-history transition events across taxa. It is through the entrainment of internal, endogenous rhythms of organisms to these external, exogenous rhythms in environment, such as cycling temperature and daylight, by which organisms can regulate and time life history transitions. Here, we review the current understanding of how photoperiod both stimulates and terminates seasonal reproduction in birds. The review describes the role of external coincidence timing, the process by which photoperiod is proposed to stimulate reproductive development. Then, the molecular basis of light detection and the photoperiodic regulation of neuroendocrine timing of seasonal reproduction in birds is presented. Current data indicates that vertebrate ancient opsin is the predominant photoreceptor for light detection by the hypothalamus, compared to neuropsin and rhodopsin. The review then connects light detection to well-characterized hypothalamic and pituitary gland molecules involved in the photoperiodic regulation of reproduction. In birds, Gonadotropin-releasing hormone synthesis and release are controlled by photoperiodic cues via thyrotropin-stimulating hormone-β (TSHβ) independent and dependent pathways, respectively. The review then highlights the role of D-box and E-box binding motifs in the promoter regions of photoperiodic genes, in particular Eyes-absent 3, as the key link between circadian clock function and photoperiodic time measurement. Based on the available evidence, the review proposes that at least two molecular programs form the basis for external coincidence timing in birds: photoperiodic responsiveness by TSHβ pathways and endogenous internal timing by gonadotropin synthesis.

High body condition score combined with a reduced lambing to ram introduction interval improves the short-term ovarian response of milking Lacaune ewes to the male effect

The male effect is an effective natural technique to induce off-season ovulation and ultimately mating or artificial insemination in small ruminants. It constitutes an alternative to hormonal treatments in conventional breeding systems and, to shift and organise the yearly production cycle, is currently the only solution complying with European organic standards. However, its associated performances are still heterogeneous, both in terms of the global response and the extent of reproductive synchronisation of the females, due to complex interactions with environmental factors that limit its use on commercial farms. This study was carried out on a French organic farm under commercial conditions to investigate, in the field and across five consecutive years, the main parameters affecting the early ovarian response to a ram effect on Lacaune dairy ewes. While the within-year binary logistic regressions yielded contrasting results, the cross-year mixed-effect binary logistic regression models clearly showed that parameters associated with the nutritional state of the animals have a profound influence on the ovarian response of the ewes. Indeed, the probabilities of a spontaneous resumption of ovarian activity before the ram effect and of an early ovarian response to the ram effect were positively associated with the body condition score, total milk production and the age of the animals, while being negatively associated with the milk production level at the 3rd milk recording. The probabilities of a spontaneous resumption of ovarian activity before the ram effect were positively associated with the interval between lambing and the introduction of the rams. Altogether, these results indicate that the ovarian performances in response to a male effect follow a bell-curve pattern with optimal performances depending upon a complex combination between photoperiodic and nutritional cues. Regarding these latter, this study highlights the major contribution of body reserves and energy balance dynamics.

Juvenile hormone as a causal factor for maternal regulation of diapause in a wasp

Most temperate multivoltine insects enter diapause, a hormonally controlled developmental suspension, in response to seasonal photoperiodic and/or thermal cues. Some insect species exhibit maternal regulation of diapause in which developmental trajectories of the offspring are determined by mothers in response to environmental cues that the mother received. Although maternally regulated diapause is common among insects, the maternal endocrinological mechanisms are largely veiled. To approach this issue, we used the jewel wasp Nasonia vitripennis, which produces non-diapause-destined offspring under long days and diapause-destined offspring under short days or low temperatures. Comparative transcriptomics of these wasps revealed possible involvement of the juvenile hormone (JH) biosynthetic cascade in maternal diapause regulation. The expression of juvenile hormone acid O-methyltransferase (jhamt) was typically downregulated in short-day wasps, and this was reflected by a reduction in haemolymph JH concentrations. RNAi targeted at jhamt reduced haemolymph JH concentration and induced wasps to produce diapause-destined offspring even under long days. In addition, topical application of JH suppressed the production of diapause-destined offspring under short days or low temperatures. These results indicate that diapause in N. vitripennis is determined by maternal jhamt expression and haemolymph JH concentration in response to day length. We therefore report a novel role for JH in insect seasonality.

NUTRITION AND REPRODUCTION IN SHEEP

High nutrition, but not overfeeding, has a positive effect on ewe reproductive capability in terms of the number of estrous cycles, length of the breeding season, greater ovulation rate, and improved lambing %. Copper deficiency hurts lambing percentage and lamb health. Manganese is required for the ovarian activity to be maintained. Protein is necessary for sheep for optimum sperm capacitation, conception rate, pregnancy, and reduced abortions. Protein insufficiency causes lower feed intake, poorer feed utilization, lower growth rate, lower milk output, and lower wool production. A possible reason for the decline in adult reproductive function is nutritionally impaired ovarian development. Functional impairment in any component of the hormone complex has a direct impact on reproduction. Factors such as photoperiod, nutrition, and social sexual cues, genetics, affect the reproductive capacity of both male and female sheep. In mammals, reproduction is energetically more demanding for the females than for the males.

Neuroendocrine regulation of reproduction in Atlantic cod (Gadus morhua): Evidence of Eya3 as an integrator of photoperiodic cues and nutritional regulation to initiate sexual maturation

Evidence from mammals and aves alludes to a possibly conserved seasonal photoperiod induced neuroendocrine cascade which stimulates subsequent sexual maturation however our understanding of this mechanism in teleosts is lacking. Unlike all teleosts studied to date, the Atlantic cod (Gadus morhua) is a short day breeder with the reduction in day-length from the summer solstice stimulating gametogenesis. Cod specific orthologues of eya3, tshβ and dio2 were identified and their expression was monitored in the brain and pituitary of cod held under either stimulated or inhibited photoperiod conditions. While no differential expression was apparent in brain dio2 &tshβ and pituitary tshβ, there was significant temporal variation in expression of pituitary eya3 under the SNP treatment, with expression level elevating in association with active gametogenesis. Under the LL treatment, sexual maturation was inhibited and there was a corresponding suppression of eya3 expression. In a second study the impact of size/energetic status on the initiation of sexual maturation was investigated. In the feed restricted population maturation was significantly suppressed (5% sexually mature) compared to the ab libitum fed stock (95% sexually mature) with there being a concomitant significant suppression in pituitary eya3 expression. Overall, these results suggest that pituitary eya3 has the potential to act as an integrator of both environmental and energetic regulation of sexual maturation of cod. Being the first account of eya3 induction in a short day breeding teleost, the conserved association with stimulation of reproduction and not seasonal state indicates that the upstream drivers which initiate the pathway differ among vertebrates according to their breeding strategies, but the pathway itself and its role in the reproductive cascade appears to be conserved across the vertebrate clade.

Phytochrome B and PHYTOCHROME INTERACTING FACTOR8 modulate seasonal growth in trees.

The seasonally synchronized annual growth cycle that is regulated mainly by photoperiod and temperature cues is a crucial adaptive strategy for perennial plants in boreal and temperate ecosystems. Phytochrome B (phyB), as a light and thermal sensor, has been extensively studied in Arabidopsis. However, the specific mechanisms for how the phytochrome photoreceptors control the phenology in tree species remain poorly understood. We characterized the functions of PHYB genes and their downstream PHYTOCHROME INTERACTING FACTOR (PIF) targets in the regulation of shade avoidance and seasonal growth in hybrid aspen trees. We show that while phyB1 and phyB2, as phyB in other plants, act as suppressors of shoot elongation during vegetative growth, they act as promoters of tree seasonal growth. Furthermore, while the Populus homologs of both PIF4 and PIF8 are involved in the shade avoidance syndrome (SAS), only PIF8 plays a major role as a suppressor of seasonal growth. Our data suggest that the PHYB-PIF8 regulon controls seasonal growth through the regulation of FT and CENL1 expression while a genome-wide transcriptome analysis suggests how, in Populus trees, phyB coordinately regulates SAS responses and seasonal growth cessation.