Short-day Photoperiod Research Articles

CsTFL1, a constitutive local repressor of flowering, modulates floral initiation by antagonising florigen complex activity in chrysanthemum

Chrysanthemums require repeated cycles of short-day (SD) photoperiod for successful anthesis, but their vegetative state is strictly maintained under long-day (LD) or night-break (NB) conditions. We have previously demonstrated that photoperiodic flowering of a wild diploid chrysanthemum (Chrysanthemum seticuspe f. boreale) is controlled by a pair of systemic floral regulators, florigen (CsFTL3) and anti-florigen (CsAFT), produced in the leaves. Here, we report the functional characterisation of a local floral regulator, CsTFL1, a chrysanthemum orthologue of TERMINAL FLOWER 1 gene in Arabidopsis. Constitutive expression of CsTFL1 in C. seticuspe (CsTFL1-ox) resulted in extremely late flowering under SD and prevented up-regulation of floral meristem identity genes in shoot tips and leaves. Bimolecular fluorescence complementation assay showed that both CsTFL1 and CsFTL3 interacted with CsFDL1, a bZIP transcription factor FD homologue, in the nucleus. The transient gene expression assay indicated that CsTFL1 suppresses flowering by directly antagonising the flower inductive activity of the CsFTL3-CsFDL1 complex. Our results suggest that strict maintenance of vegetative state under non-inductive photoperiod is achieved by the coordinated action of both the systemic floral inhibitor and local floral inhibitor CsTFL1, which is constitutively expressed in shoot tips.

Global transcriptional dynamics of diapause induction in non-blood-fed and blood-fed Aedes albopictus.

Background Aedes albopictus is a vector of increasing public health concern due to its rapid global range expansion and ability to transmit Dengue virus, Chikungunya virus and a wide range of additional arboviruses. Traditional vector control strategies have been largely ineffective against Ae. albopictus and novel approaches are urgently needed. Photoperiodic diapause is a crucial ecological adaptation in a wide range of temperate insects. Therefore, targeting the molecular regulation of photoperiodic diapause or diapause-associated physiological processes could provide the basis of novel approaches to vector control.Methodology/Principal FindingsWe investigated the global transcriptional profiles of diapause induction in Ae. albopictus by performing paired-end RNA-Seq of biologically replicated libraries. We sequenced RNA from whole bodies of adult females reared under diapause-inducing and non-diapause-inducing photoperiods either with or without a blood meal. We constructed a comprehensive transcriptome assembly that incorporated previous assemblies and represents over 14,000 annotated dipteran gene models. Mapping of sequence reads to the transcriptome identified differential expression of 2,251 genes in response to diapause-inducing short-day photoperiods. In non-blood-fed females, potential regulatory elements of diapause induction were transcriptionally up-regulated, including two of the canonical circadian clock genes, timeless and cryptochrome 1. In blood-fed females, genes in metabolic pathways related to energy production and offspring provisioning were differentially expressed under diapause-inducing conditions, including the oxidative phosphorylation pathway and lipid metabolism genes.Conclusions/SignificanceThis study is the first to utilize powerful RNA-Seq technologies to elucidate the transcriptional basis of diapause induction in any insect. We identified candidate genes and pathways regulating diapause induction, including a conserved set of genes that are differentially expressed as part of the diapause program in a diverse group of insects. These genes provide candidates whose diapause-associated function can be further interrogated using functional genomics approaches in Ae. albopictus and other insects.

Why is the number of days required for induction of adult diapause in the linden bug Pyrrhocoris apterus fewer in the larval than in the adult stage?

Adult females of Pyrrhocoris apterus, programmed for diapause by short-day (SD) photoperiod and those programmed for reproduction by long-day (LD) retain photoperiodic information in continuous darkness (DD) until death. However, if the interruption of SD by DD is made in the course of diapause programming in adults, then the incidence of diapause depends on the number of SD cycles received before DD, with no evidence that the photoperiodic clock is free-running at DD to complete diapause induction. These results indicate that the photoperiodic clock is stopped after transfer to DD and the information accumulated before transfer to DD is maintained. Diapause programming in the adult stage requires 9–10 SD cycles to induce diapause in 80% of individuals. However, if the diapause programming starts after ecdysis of LD-larvae to the last instar, only 3 SD cycles before transfer to DD are required for diapause in 80% of individuals. Surprisingly, if the newly ecdysed last instar LD-larvae, sensitive to photoperiod, are transferred to DD (thus they did not experience any SD), diapause occurs in 40% of the individuals. Thus, diapause ‘information’ is present in LD-larvae and is responsible for a lower number of SD required for diapause induction in the larval than in the adult stage.

Arabidopsis thaliana HomeoBox 1 (AtHB1), a Homedomain-Leucine Zipper I (HD-Zip I) transcription factor, is regulated by PHYTOCHROME-INTERACTING FACTOR 1 to promote hypocotyl elongation.

Arabidopsis thaliana HomeoBox 1 (AtHB1) is a homeodomain-leucine zipper transcription factor described as a transcriptional activator with unknown function. Its role in A. thaliana development was investigated. AtHB1 expression was analyzed in transgenic plants bearing its promoter region fused to reporter genes. Knock-down mutant and overexpressor plant phenotypes were analyzed in different photoperiod regimes. AtHB1 was mainly expressed in hypocotyls and roots and up-regulated in seedlings grown under a short-day photoperiod. AtHB1 knock-down mutants and overexpressors showed shorter and longer hypocotyls, respectively, than wild type (WT). AtHB1 transcript levels were lower in PHYTOCHROME-INTERACTING FACTOR 1 (PIF1) mutants than in controls, suggesting that AtHB1 is regulated by PIF1 in hypocotyls. β-glucuronidase (GUS) activity in Nicotiana benthamiana leaves cotransformed with PromAtHB1::GUS and 35S::PIF1 indicated that PIF1 induces AtHB1 expression. Hypocotyl lenght was measured in seedlings of athb1, pif1, or double athb1/pif1 mutants and PIF1 or AtHB1 overexpressors in WT, athb1 or pif1 backgrounds, both in short- or long-day. These analyses allowed us to determine that AtHB1 is a factor acting downstream of PIF1. Finally, a transcriptome analysis of athb1 mutant hypocotyls revealed that AtHB1 regulates genes involved in cell wall composition and elongation. The results suggest that AtHB1 acts downstream of PIF1 to promote hypocotyl elongation, especially in response to short-day photoperiods.

Exploring avian deep-brain photoreceptors and their role in activating the neuroendocrine regulation of gonadal development.

In the eyes of mammals, specialized photoreceptors called intrinsically photosensitive retinal ganglion cells (ipRGC) have been identified that sense photoperiodic or daylight exposure, providing them over time with seasonal information. Detectors of photoperiods are critical in vertebrates, particularly for timing the onset of reproduction each year. In birds, the eyes do not appear to monitor photoperiodic information; rather, neurons within at least 4 different brain structures have been proposed to function in this capacity. Specialized neurons, called deep brain photoreceptors (DBP), have been found in the septum and 3 hypothalamic areas. Within each of the 4 brain loci, one or more of 3 unique photopigments, including melanopsin, neuropsin, and vertebrate ancient opsin, have been identified. An experiment was designed to characterize electrophysiological responses of neurons proposed to be avian DBP following light stimulation. A second study used immature chicks raised under short-day photoperiods and transferred to long day lengths. Gene expression of photopigments was then determined in 3 septal-hypothalamic regions. Preliminary electrophysiological data obtained from patch-clamping neurons in brain slices have shown that bipolar neurons in the lateral septal organ responded to photostimulation comparable with mammalian ipRGC, particularly by showing depolarization and a delayed, slow response to directed light stimulation. Utilizing real-time reverse-transcription PCR, it was found that all 3 photopigments showed significantly increased gene expression in the septal-hypothalamic regions in chicks on the third day after being transferred to long-day photoperiods. Each dissected region contained structures previously proposed to have DBP. The highly significant increased gene expression for all 3 photopigments on the third, long-day photoperiod in brain regions proposed to contain 4 structures with DBP suggests that all 3 types of DBP (melanopsin, neuropsin, and vertebrate ancient opsin) in more than one neural site in the septal-hypothalamic area are involved in reproductive function. The neural response to light of at least 2 of the proposed DBP in the septal/hypothalamic region resembles the primitive, functional, sensory ipRGC well characterized in mammals.

Molecular evolution and phylogenetic analysis of eight COL superfamily genes in group I related to photoperiodic regulation of flowering time in wild and domesticated cotton (Gossypium) species.

Flowering time is an important ecological trait that determines the transition from vegetative to reproductive growth. Flowering time in cotton is controlled by short-day photoperiods, with strict photoperiod sensitivity. As the CO-FT (CONSTANS-FLOWER LOCUS T) module regulates photoperiodic flowering in several plants, we selected eight CONSTANS genes (COL) in group I to detect their expression patterns in long-day and short-day conditions. Further, we individually cloned and sequenced their homologs from 25 different cotton accessions and one outgroup. Finally, we studied their structures, phylogenetic relationship, and molecular evolution in both coding region and three characteristic domains. All the eight COLs in group I show diurnal expression. In the orthologous and homeologous loci, each gene structure in different cotton species is highly conserved, while length variation has occurred due to insertions/deletions in intron and/or exon regions. Six genes, COL2 to COL5, COL7 and COL8, exhibit higher nucleotide diversity in the D-subgenome than in the A-subgenome. The Ks values of 98.37% in all allotetraploid cotton species examined were higher in the A-D and At-Dt comparison than in the A-At and D-Dt comparisons, and the Pearson’s correlation coefficient (r) of Ks between A vs. D and At vs. Dt also showed positive, high correlations, with a correlation coefficient of at least 0.797. The nucleotide polymorphism in wild species is significantly higher compared to G. hirsutum and G. barbadense, indicating a genetic bottleneck associated with the domesticated cotton species. Three characteristic domains in eight COLs exhibit different evolutionary rates, with the CCT domain highly conserved, while the B-box and Var domain much more variable in allotetraploid species. Taken together, COL1, COL2 and COL8 endured greater selective pressures during the domestication process. The study improves our understanding of the domestication-related genes/traits during cotton evolutionary process.

Effects of short-day treatment on long-term growth performance and maturation of farmed Arctic charr Salvelinus alpinus reared in brackish water.

The effects of a 6 week short-day photoperiod followed by continuous light, applied during the juvenile phase of Arctic charr Salvelinus alpinus in fresh water on smoltification and on the long-term growth and maturity following transfer to brackish water (BW) (constant salinity of either 17 and 27 or increasing salinity in steps from 17 to 27) were investigated. Prior to salinity transfer, the juveniles were either reared at continuous light (C group) or reared for 6 weeks on a short day (8L:16D, S group) followed by continuous light (24L:0D). Increased salinity had negative effect on growth, with female fish reared at 17 salinity weighing 19 and 27% more than the salinity-step group (17-27) and the 27 salinity group, respectively. The stepwise acclimation to salinity had limited advantage in terms of growth rate. Short photoperiod for 6 weeks (November to January) followed by continuous light improved growth, but not seawater (SW) tolerance. Gill Na(+) , K(+) -ATPase activity and plasma Na(+) levels changed with time, indicating some variation in osmoregulatory capacity during the experimental period. Overall, there appear to be interactive effects on maturation from applying short-day photoperiod followed by rearing at higher salinities. Plasma leptin varied with time and may be linked to stress caused by the observed variations in osmoregulatory ability. It is concluded that changes in growth rates observed in this study are mainly related to rearing salinity with higher growth rates at lower salinities. Short-day photoperiod has some growth-inducing effects but did not improve SW tolerance. Farmers of S. alpinus using BW for land-based rearing should keep salinity at moderate and stable levels according to these results to obtain best growth.

Regulation of arabidopsis flowering by the histone mark readers MRG1/2 via interaction with CONSTANS to modulate FT expression.

Day-length is important for regulating the transition to reproductive development (flowering) in plants. In the model plant Arabidopsis thaliana, the transcription factor CONSTANS (CO) promotes expression of the florigen FLOWERING LOCUS T (FT), constituting a key flowering pathway under long-day photoperiods. Recent studies have revealed that FT expression is regulated by changes of histone modification marks of the FT chromatin, but the epigenetic regulators that directly interact with the CO protein have not been identified. Here, we show that the Arabidopsis Morf Related Gene (MRG) group proteins MRG1 and MRG2 act as H3K4me3/H3K36me3 readers and physically interact with CO to activate FT expression. In vitro binding analyses indicated that the chromodomains of MRG1 and MRG2 preferentially bind H3K4me3/H3K36me3 peptides. The mrg1 mrg2 double mutant exhibits reduced mRNA levels of FT, but not of CO, and shows a late-flowering phenotype under the long-day but not short-day photoperiod growth conditions. MRG2 associates with the chromatin of FT promoter in a way dependent of both CO and H3K4me3/H3K36me3. Vice versa, loss of MRG1 and MRG2 also impairs CO binding at the FT promoter. Crystal structure analyses of MRG2 bound with H3K4me3/H3K36me3 peptides together with mutagenesis analysis in planta further demonstrated that MRG2 function relies on its H3K4me3/H3K36me3-binding activity. Collectively, our results unravel a novel chromatin regulatory mechanism, linking functions of MRG1 and MRG2 proteins, H3K4/H3K36 methylations, and CO in FT activation in the photoperiodic regulation of flowering time in plants.

D2-like dopamine receptors mediate regulation of pupal diapause in Chinese oak silkmothAntheraea pernyi

The present study investigated the pharmacological properties of dopamine receptors that functioned in the termination of pupal diapause in the Chinese oak silkmoth, Antheraea pernyi (Lepidoptera: Saturniidae). Dopamine receptors are classified according to their structure and function into two subfamilies as D1- and D2-like receptors. D1-like receptors activate, whereas D2-like receptors inhibit, adenylate cyclase. We examined the effects of agonists and antagonists selective for D1- and D2-like receptors on the diapause state. As A. pernyi is a long-day species, pupal diapause is maintained during short days and can be terminated by exposure to a long-day photoperiod. The D2-like receptor-selective agonist quinpirole delayed the timing of adult emergence under long days, and the D2-receptor-selective antagonist sulpiride terminated pupal diapause even under a short-day photoperiod. The D1-like receptor-selective agonist and antagonist, SKF-38393 and SCH-23390, respectively, caused no significant effects on diapause pupae. These results suggest that not D1- but D2-like receptors mediated diapause regulation in A. pernyi. This dopamine pathway appeared to block the termination of pupal diapause. Furthermore, the actions of the cAMP analog 8-CPT-cAMP and dopamine receptor antagonists upon diapause pupae were similar, which supports the notion that D2-like receptors involved in diapause of this insect prevent adenylate cyclase from producing cAMP like vertebrate D2-like receptors. Taken together, our findings suggest that dopamine blocked diapause termination through D2-like receptors that inhibited adenylate cyclase in A. pernyi. During short days under which diapause was maintained in pupae, the dopaminergic mechanism might be stimulated to suppress cAMP levels in cells regulating diapause.

EARLY FLOWERING3 Regulates Flowering in Spring Barley by Mediating Gibberellin Production and FLOWERING LOCUS T Expression

EARLY FLOWERING3 (ELF3) is a circadian clock gene that contributes to photoperiod-dependent flowering in plants, with loss-of-function mutants in barley (Hordeum vulgare), legumes, and Arabidopsis thaliana flowering early under noninductive short-day (SD) photoperiods. The barley elf3 mutant displays increased expression of FLOWERING LOCUS T1 (FT1); however, it remains unclear whether this is the only factor responsible for the early flowering phenotype. We show that the early flowering and vegetative growth phenotypes of the barley elf3 mutant are strongly dependent on gibberellin (GA) biosynthesis. Expression of the central GA biosynthesis gene, GA20oxidase2, and production of the bioactive GA, GA1, were significantly increased in elf3 leaves under SDs, relative to the wild type. Inhibition of GA biosynthesis suppressed the early flowering of elf3 under SDs independently of FT1 and was associated with altered expression of floral identity genes at the developing apex. GA is also required for normal flowering of spring barley under inductive photoperiods, with chemical and genetic attenuation of the GA biosynthesis and signaling pathways suppressing inflorescence development under long-day conditions. These findings illustrate that GA is an important floral promoting signal in barley and that ELF3 suppresses flowering under noninductive photoperiods by blocking GA production and FT1 expression.

Effect of prepartum photoperiod and melatonin feeding on milk production and prolactin concentration in dairy heifers and cows

Holstein multiparous cows (n=29) and primiparous heifers (n=32) calving over a 1-yr period were subjected to photoperiod-melatonin treatments according to a 2×3 factorial design. Starting 8wk before expected calving, all animals were subjected to 1 of the following treatments: 8h of light and 16h of dark (8L:16D), 16h of light and 8h of dark (16L:8D), or 16L:8D plus melatonin feeding (16L:8D-melatonin). Each day at 1355h, the animals in the melatonin treatment received orally a gelatin capsule containing 25mg of melatonin. The treatments ended at calving, when the animals were moved to the lactation barn; all animals were then subjected to about 16h of light per day. At the beginning and end of the treatment period before calving, blood samples were taken from 6heifers and 6cows through a jugular cannula for 24h at 30-min intervals to monitor serum melatonin and prolactin concentrations. Milk production in the heifers was not affected by the photoperiod treatments. Early-lactation milk production was higher in the cows exposed to the short-day photoperiod than in those exposed to a long-day photoperiod (16L:8D and 16L:8D-melatonin), with averages of 36.7±0.9, 33.1±0.8, and 34.1±0.9kg/d for 8L:16D, 16L:8D, and 16L:8D-melatonin, respectively. Photoperiod had no effect on late-lactation milk production in the cows. During lactation, the dry matter intake of heifers was not affected by the treatments, but dry matter intake of the cows exposed to a short-day photoperiod was greater than that of the cows exposed to a long-day photoperiod. Feed efficiency of heifers was improved by short-day photoperiod. During the treatment period, prolactin concentration was lower in the animals exposed to a short-day photoperiod than in those exposed to a long-day photoperiod, was lower with the 16L:8D-melatonin treatment than with the 16L:8D treatment, and tended to be lower with the 8L:16D treatment than with the 16L:8D-melatonin treatment, with averages of 3.5±0.8, 9.9±0.8, and 6.0±0.8ng/mL for 8L:16D, 16L:8D, and 16L:8D-melatonin, respectively. In early lactation, prolactin concentration was lower in the heifers exposed to the 16L:8D photoperiod during the dry period than in those exposed to the 8L:16D photoperiod or fed melatonin. In conclusion, a short-day photoperiod during the dry period transiently increases milk production of cows and the feed efficiency of heifers in the following lactation. However, melatonin cannot be used to mimic a short-day photoperiod during the dry period.

Identification of photoperiod-regulated gene in soybean and functional analysis in Nicotiana benthamiana.

Soybean (Glycine max) is a short-day crop and the photoperiod is a crucial factor regulating its flowering time. To investigate the molecular mechanism controlling the flowering time by photoperiod in soybean, cDNA-amplified fragment length polymorphism (cDNA-AFLP) was used to identify photoperiod-regulated genes in leaves of soybean growing under short-day length, neutral photoperiod and long-day length. A total of 36 transcript-derived fragments (TDFs) were identified to be regulated by photoperiod. Among them, 26 TDFs were homologues of genes with known function. These genes are involved in secondary metabolism, cellular metabolism, cell wall components metabolism, ion transport and hormone signalling. Silencing of the homologue genes in Nicotiana benthamiana for 14 TDFs was conducted by virus-induced gene silencing. The flowering time was delayed by silencing of the genes encoding rhodanese and 40S ribosomal protein S4 (RPS4). The results indicated that rhodanese and RPS4 probably play important roles in regulating flowering time.

Effect of Exercise on Photoperiod-Regulated Hypothalamic Gene Expression and Peripheral Hormones in the Seasonal Dwarf Hamster Phodopus sungorus

The Siberian hamster (Phodopus sungorus) is a seasonal mammal responding to the annual cycle in photoperiod with anticipatory physiological adaptations. This includes a reduction in food intake and body weight during the autumn in anticipation of seasonally reduced food availability. In the laboratory, short-day induction of body weight loss can be reversed or prevented by voluntary exercise undertaken when a running wheel is introduced into the home cage. The mechanism by which exercise prevents or reverses body weight reduction is unknown, but one hypothesis is a reversal of short-day photoperiod induced gene expression changes in the hypothalamus that underpin body weight regulation. Alternatively, we postulate an exercise-related anabolic effect involving the growth hormone axis. To test these hypotheses we established photoperiod-running wheel experiments of 8 to 16 weeks duration assessing body weight, food intake, organ mass, lean and fat mass by magnetic resonance, circulating hormones FGF21 and insulin and hypothalamic gene expression. In response to running wheel activity, short-day housed hamsters increased body weight. Compared to short-day housed sedentary hamsters the body weight increase was accompanied by higher food intake, maintenance of tissue mass of key organs such as the liver, maintenance of lean and fat mass and hormonal profiles indicative of long day housed hamsters but there was no overall reversal of hypothalamic gene expression regulated by photoperiod. Therefore the mechanism by which activity induces body weight gain is likely to act largely independently of photoperiod regulated gene expression in the hypothalamus.

Accumulation of Biomass and Compositional Change Over the Growth Season for Six Photoperiod Sorghum Lines

Biomass sorghums [Sorghum bicolor (L.) Moench] are short-day photoperiod sensitive (PS) types, meaning that the crop will grow vegetatively late into the fall season in subtropical and temperate environments. This feature results in high biomass yield potential and mitigates drought susceptibility. The objective of this study is to assess biomass growth patterns and associated changes in composition over a growing season for PS sorghum. The experiment had a split-plot design with two replications, six PS sorghum genotypes, and 13 harvest dates. Harvest started at 60 days after planting (DAP) and continued every 15 days thereafter in both College Station (CS) and Corpus Christi (CC) in Texas, 2010. At each harvest, dry biomass yield, plant height and biomass composition (percent lignin and cellulose) were measured. For all genotypes, biomass accumulation followed a standard growth pattern which included an early lag phase, followed by a log phase of growth and finally, a general reduction in the rate of accumulation. The early lag phase ended at approximately 70 DAP, the log phase of growth ended at approximately 125 DAP, and biomass yields maximized between 180 and 225 DAP. The highest yielding genotype produced 24 Mg ha−1. Plant heights up to 400 cm were also measured between 180 and 225 DAP. Plant height and biomass yield patterns were similar, indicating that height is important to increase yield. Lignin and cellulose concentrations increased with time; at the highest yields (between 180 and 225 DAP), maximum lignin content were 14.5 to 15.5 % and maximum cellulose content was 31 to 32 %. As with yield potential, significant differences were detected for composition as well. The growth curves indicate that PS biomass sorghum yields sufficiently and can be harvested as early as 130 DAP with maximum sorghum biomass accumulation occurring between 180 and 225 days. Thus, with careful selection and deployment of biomass sorghum hybrids, the harvest season of biomass sorghum can be extended over a 3-month period in southern regions of the US

Roles of Gibberellin Catabolism and Signaling in Growth and Physiological Response to Drought and Short-Day Photoperiods in Populus Trees

Survival and productivity of perennial plants in temperate zones are dependent on robust responses to prolonged and seasonal cycles of unfavorable conditions. Here we report whole-genome microarray, expression, physiological, and transgenic evidence in hybrid poplar (Populus tremula × Populus alba) showing that gibberellin (GA) catabolism and repressive signaling mediates shoot growth inhibition and physiological adaptation in response to drought and short-day (SD) induced bud dormancy. Both water deprivation and SDs elicited activation of a suite of poplar GA2ox and DELLA encoding genes. Poplar transgenics with up-regulated GA 2-oxidase (GA2ox) and DELLA domain proteins showed hypersensitive growth inhibition in response to both drought and SDs. In addition, the transgenic plants displayed greater drought resistance as evidenced by increased pigment concentrations (chlorophyll and carotenoid) and reductions in electrolyte leakage (EL). Comparative transcriptome analysis using whole-genome microarray showed that the GA-deficiency and GA-insensitivity, SD-induced dormancy, and drought response in poplar share a common regulon of 684 differentially-expressed genes, which suggest GA metabolism and signaling plays a role in plant physiological adaptations in response to alterations in environmental factors. Our results demonstrate that GA catabolism and repressive signaling represents a major route for control of growth and physiological adaptation in response to immediate or imminent adverse conditions.

PIF1 promotes phytochrome-regulated growth under photoperiodic conditions in Arabidopsis together with PIF3, PIF4, and PIF5

Seedlings growing under diurnal conditions display maximal growth at the end of the night in short-day (SD) photoperiods. Current evidence indicates that this behaviour involves the action of PHYTOCHROME-INTERACTING FACTOR 3 (PIF3) together with PIF4 and PIF5, through direct regulation of growth-related genes at dawn coinciding with a PIF3 accumulation peak generated by phytochrome-imposed oscillations in protein abundance. Here, to assess how alterations in PIF3 levels impact seedling growth, the night-specific accumulation of PIF3 was modulated by releasing SD-grown seedlings into continuous light, or by exposing them to a phytochrome-inactivating end-of-day far-red pulse (EOD-FRp). The data show a strong direct correlation between PIF3 accumulation, PIF3-regulated induction of growth-related genes, and hypocotyl elongation, and suggest that growth promotion in SD conditions involves factors other than PIF3, PIF4, and PIF5. Using a pif1 mutant, evidence is provided that PIF1 also contributes to inducing hypocotyl elongation during the dark period under diurnal conditions. PIF1 displayed constitutive transcript levels in SD conditions, suggesting that phytochrome-imposed oscillations in PIF1 protein abundance determine its accumulation and action during the night, similar to PIF3 and in contrast to PIF4 and PIF5, which oscillate diurnally due to a combination of circadian clock-regulated transcription and light control of protein accumulation. Furthermore, using single and higher order pif mutants, the relative contribution of each member of the PIF quartet to the regulation of morphogenesis and the expression of selected growth marker genes under SD conditions, or under SD conditions supplemented with an EOD-FRp, is defined. Collectively, the data indicate that PIF1, PIF3, PIF4, and PIF5 act together to promote and optimize growth under photoperiodic conditions.

MicroRNA156: A Potential Graft-Transmissible MicroRNA That Modulates Plant Architecture and Tuberization in Solanum tuberosum ssp. andigena

MicroRNA156 (miR156) functions in maintaining the juvenile phase in plants. However, the mobility of this microRNA has not been demonstrated. So far, only three microRNAs, miR399, miR395, and miR172, have been shown to be mobile. We demonstrate here that miR156 is a potential graft-transmissible signal that affects plant architecture and tuberization in potato (Solanum tuberosum). Under tuber-noninductive (long-day) conditions, miR156 shows higher abundance in leaves and stems, whereas an increase in abundance of miR156 has been observed in stolons under tuber-inductive (short-day) conditions, indicative of a photoperiodic control. Detection of miR156 in phloem cells of wild-type plants and mobility assays in heterografts suggest that miR156 is a graft-transmissible signal. This movement was correlated with changes in leaf morphology and longer trichomes in leaves. Overexpression of miR156 in potato caused a drastic phenotype resulting in altered plant architecture and reduced tuber yield. miR156 overexpression plants also exhibited altered levels of cytokinin and strigolactone along with increased levels of LONELY GUY1 and StCyclin D3.1 transcripts as compared with wild-type plants. RNA ligase-mediated rapid amplification of complementary DNA ends analysis validated SQUAMOSA PROMOTER BINDING-LIKE3 (StSPL3), StSPL6, StSPL9, StSPL13, and StLIGULELESS1 as targets of miR156. Gel-shift assays indicate the regulation of miR172 by miR156 through StSPL9. miR156-resistant SPL9 overexpression lines exhibited increased miR172 levels under a short-day photoperiod, supporting miR172 regulation via the miR156-SPL9 module. Overall, our results strongly suggest that miR156 is a phloem-mobile signal regulating potato development.

Effects of photoperiod on food intake, activity and metabolic rate in adult neutered male cats.

With the continued rise in feline obesity, novel weight management strategies are needed. To date, strategies aimed at altering physical activity, an important factor in weight maintenance, have been lacking. Photoperiod is known to cause physiological changes in seasonal mammals, including changes in body weight (BW) and reproductive status. Thus, our objective was to determine the effect of increased photoperiod (longer days) on voluntary physical activity levels, resting metabolic rate (RMR), food intake required to maintain BW, and fasting serum leptin and ghrelin concentrations in adult cats. Eleven healthy, adult, neutered, male domestic shorthair cats were used in a randomized crossover design study. During two 12-week periods, cats were exposed to either a short-day (SD) photoperiod of 8 h light: 16 h dark or a long-day (LD) photoperiod of 16 h light: 8 h dark. Cats were fed a commercial diet to maintain baseline BW. In addition to daily food intake and twice-weekly BW, RMR (via indirect calorimetry), body composition [via dual-energy X-ray absorptiometry (DEXA)] and physical activity (via Actical activity monitors) were measured at week 0 and 12 of each period. Fasting serum leptin and ghrelin concentrations were measured at week 0, 6 and 12 of each period. Average hourly physical activity was greater (p = 0.008) in LD vs. SD cats (3770 vs. 3129 activity counts/h), which was primarily due to increased (p < 0.001) dark period activity (1188 vs. 710 activity counts/h). This corresponded to higher (p < 0.0001) daily metabolizable energy intake (mean over 12-week period: 196 vs. 187 kcal/day), and increased (p = 0.048) RMR in LD cats (9.02 vs. 8.37 kcal/h). Body composition, serum leptin and serum ghrelin were not altered by photoperiod. More research is needed to determine potential mechanisms by which these physiological changes occurred and how they may apply to weight management strategies.

Ectopic Expression of a WRKY Homolog from Glycine soja Alters Flowering Time in Arabidopsis

Flowering is a critical event in the life cycle of plants; the WRKY-type transcription factors are reported to be involved in many developmental processes sunch as trichome development and epicuticular wax loading, but whether they are involved in flowering time regulation is still unknown. Within this study, we provide clear evidence that GsWRKY20, a member of WRKY gene family from wild soybean, is involved in controlling plant flowering time. Expression of GsWRKY20 was abundant in the shoot tips and inflorescence meristems of wild soybean. Phenotypic analysis showed that GsWRKY20 over-expression lines flowered earlier than the wild-type plants under all conditions: long-day and short-day photoperiods, vernalization, or exogenous GA3 application, indicating that GsWRKY20 may mainly be involved in an autonomous flowering pathway. Further analyses by qRT-PCR and microarray suggests that GsWRKY20 accelerating plant flowering might primarily be through the regulation of flowering-related genes (i.e., FLC, FT, SOC1 and CO) and floral meristem identity genes (i.e., AP1, SEP3, AP3, PI and AG). Our results provide the evidence demonstrating the effectiveness of manipulating GsWRKY20 for altering plant flowering time.

Deletion of chloroplast NADPH-dependent thioredoxin reductase results in inability to regulate starch synthesis and causes stunted growth under short-day photoperiods.

Plastid-localized NADPH-dependent thioredoxin reductase C (NTRC) is a unique NTR enzyme containing both reductase and thioredoxin domains in a single polypeptide. Arabidopsis thaliana NTRC knockout lines (ntrc) show retarded growth, especially under short-day (SD) photoperiods. This study identified chloroplast processes that accounted for growth reduction in SD-acclimated ntrc. The strongest reduction in ntrc growth occurred under photoperiods with nights longer than 14h, whereas knockout of the NTRC gene did not alter the circadian-clock-controlled growth of Arabidopsis. Lack of NTRC modulated chloroplast reactive oxygen species (ROS) metabolism, but oxidative stress was not the primary cause of retarded growth of SD-acclimated ntrc. Scarcity of starch accumulation made ntrc leaves particularly vulnerable to photoperiods with long nights. Direct interaction of NTRC and ADP-glucose pyrophosphorylase, a key enzyme in starch synthesis, was confirmed by yeast two-hybrid analysis. The ntrc line was not able to maximize starch synthesis during the light period, which was particularly detrimental under SD conditions. Acclimation of Arabidopsis to SD conditions also involved an inductive rise of ROS production in illuminated chloroplasts that was not counterbalanced by the activation of plastidial anti-oxidative systems. It is proposed that knockout of NTRC challenges redox regulation of starch synthesis, resulting in stunted growth of the mutant lines acclimated to the SD photoperiod.