Molecular cloning and functional analysis of a blue light receptor gene MdCRY2 from apple (Malus domestica)

The wavelength dependence of oxygen-evolving complex inactivation in Zosteramarina

Zostera marina, a critical keystone marine angiosperm species in coastal seagrass meadows, possesses a photosensitive oxygen evolving complex (OEC). In harsh environments, the photoinactivation of the Z. marina OEC may lead to population declines. However, the factors underlying this photosensitivity remain unclear. Therefore, this study was undertaken to elucidate the elements contributing to Z. marina OEC photosensitivity. Our results demonstrated a gradual decrease in photosystem II performance towards shorter wavelengths, especially blue light and ultraviolet radiation. This phenomenon was characterized by a reduction in Fv/Fm and the rate of O2 evolution, as well as increased fluorescence at 0.3 ms on the OJIP curve. Furthermore, exposure to shorter light wavelengths and longer exposure durations significantly reduced the relative abundance of the OEC peripheral proteins, indicating OEC inactivation. Analyses of light-screening substances revealed that carotenoids, which increased most notably under 420 nm light, might primarily serve as thermal dissipators instead of efficient light filters. In contrast, anthocyanins reacted least to short-wavelength light, in terms of changes to both their content and the expression of genes related to their biosynthesis. Additionally, the levels of aromatically acylated anthocyanins remained consistent across blue-, white-, and red-light treatments. These findings suggest that OEC photoinactivation in Z. marina may be linked to inadequate protection against short-wavelength light, a consequence of insufficient synthesis and aromatic acylation modification of anthocyanins.

Recent advances in plant-based bioproduction

Unable to move on their own, plants have acquired the ability to produce a wide variety of low molecular weight compounds to survive against various stresses. It is estimated that there are as many as one million different kinds. Plants also have the ability to accumulate high levels of proteins. Although plant-based bioproduction has traditionally relied on classical tissue culture methods, the attraction of bioproduction by plants is increasing with the development of omics and bioinformatics and other various technologies, as well as synthetic biology. This review describes the current status and prospects of these plant-based bioproduction from five advanced research topics, (i) de novo production of plant-derived high value terpenoids in engineered yeast, (ii) biotransformation of plant-based materials, (iii) genome editing technology for plant-based bioproduction, (iv) environmental effect of metabolite production in plant factory, and (v) molecular pharming.

OsCRY2 and OsFBO10 co-regulate photomorphogenesis and photoperiodic flowering in indica rice

Cryptochromes (CRYs) are a class of photoreceptors that perceive blue/ultraviolet-A light of the visible spectrum to mediate a vast number of physiological responses in bacteria, fungi, animals and plants. In the present study, we have characterized OsCRY2 in a photoperiod sensitive indica variety, Basmati 370, by generating and analyzing overexpression (OE) and knock-down (KD) transgenic lines. The OsCRY2^OE lines displayed dwarfism as shown in their reduced plant height and leaf length, attributed largely by an overall reduction in their cell size. The OsCRY2^OE lines flowered significantly earlier and showed shorter and broader seeds with an overall reduced seed weight. The OsCRY2^KD lines showed contrasting phenotypes, such as increased plant height and delayed flowering, however, decreased seed size and weight were also observed in the KD lines, along with reduced spikelet fertility and high seed shattering rate in mature panicles. Novel interactions were confirmed between OsCRY2 and members of ZEITLUPE family of blue/ultraviolet-A light photoreceptors, encoded by OsFBO8, OsFBO9 and OsFBO10 which are orthologous to ZEITLUPE (ZTL), LOV KELCH PROTEIN2 (LKP2) and FLAVIN BINDING, KELCH REPEAT F-BOX1 (FKF1), respectively, of Arabidopsis thaliana. Since FKF1 is known to play a role in regulating photoperiodic flowering, OsFBO10 was chosen for further studies. OsCRY2 and OsFBO10 interacted in the nucleus and cytoplasm of the cell and cross-regulated the expression of each other. They were also found to regulate the expression of several genes involved in photoperiodic flowering in rice. Both OsCRY2 and OsFBO10 played a positive role in photomorphogenic responses in different light conditions. The physical interaction of OsCRY2 with OsFBO10, their involvement in common physiological and developmental pathways and their cross-regulation of each other suggest that the two photoreceptors may regulate common developmental pathways in plants, either jointly or redundantly.

CRY2 gene of rice (Oryza sativa subsp. indica) encodes a blue light sensory receptor involved in regulating flowering, plant height and partial photomorphogenesis in dark

OsiCRY2 is involved in light-regulated plant development and plays a role in regulating photomorphogenesis, plant height, flowering and most strikingly partial photomorphogenesis in dark. Cryptochrome 2 (CRY2), the blue/UV-A light photoreceptor in plants, has been reported to regulate photoperiod-dependent flowering and seedling photomorphogenesis (under low-intensity light). Among monocots, CRY2 has been reported from japonica rice, wheat, sorghum and barley. The two sub-species of rice, indica and japonica, exhibit a high degree of genetic variation and morphological and physiological differences. This article describes the characterization of CRY2 of indica rice (OsiCRY2). While the transcript levels of OsiCRY2 did not change significantly under blue light, its protein levels were found to decline with increased time duration under blue light. For phenotypic characterization, OsiCRY2 over-expression (OX) transgenics were generated in Oryza sativa Pusa Sugandh 2 (PS2) cultivar, a highly scented Basmati cultivar. The OsiCRY2^OX transgenics displayed shorter coleoptiles and dwarfism than wild-type under blue light, white, and far-red light. Interestingly, even the dark-grown transgenics were shorter, concomitant with higher OsiCRY2 protein levels in transgenics than wild-type. Histological analysis revealed that the decrease in the length of the seedlings was due to a decrease in the length of the epidermal cells. The fully mature rice transgenics were shorter than the untransformed plants but flowered at the same time as wild-type. However, the OsiCRY2 Arabidopsis over-expressors exhibited early flowering by 10-15 days, indicating the potential and conservation of function of OsiCRY2. The whole-genome transcriptome profiling of rice transgenics revealed the differential up-regulation of several light-regulated genes in dark-grown coleoptiles. These data provide evidence that OsiCRY2 regulates photomorphogenesis, plant height, and flowering in indica rice.

Blue Light Simultaneously Induces Peel Anthocyanin Biosynthesis and Flesh Carotenoid/Sucrose Biosynthesis in Mango Fruit

Previous studies focused on the effects of light on fruit appearance, especially the peel color. However, the effect of light on fruit internal quality and the underlying mechanisms are unclear. In this study, we analyzed the effects of blue light on the appearance and internal quality of mango fruit (Mangifera indica L.). Blue light simultaneously induced peel anthocyanin and flesh sucrose/carotenoid biosynthesis in mango fruit. Analyses of co-expression networks and gene expression trends in mango fruit peel and flesh identified candidate genes, including transcription factor genes, involved in blue light-regulated anthocyanin, carotenoid, and sucrose biosynthesis pathways. Key blue light signaling-related genes (MiCRY and MiHY5) and blue light-triggered phytohormones were involved in these pathways. Additionally, there were common and tissue-specific pathways for the blue light-promoted accumulation of anthocyanins, carotenoids, and sucrose. Our results provide new insights into the regulatory effects of light on the appearance and internal quality of mango fruit.

Integrated transcriptome and metabolome analysis reveals the anthocyanin biosynthesis mechanisms in blueberry (Vaccinium corymbosum L.) leaves under different light qualities

INTRODUCTION

Blueberry (Vaccinium corymbosum L.) is a popular fruit with an abundance of anthocyanins in its leaves and fruits. Light is one of the pivotal environmental elements that affects plant growth and development, but the regulatory mechanism between light quality and anthocyanin formation is poorly understood.

METHODS

An integrated transcriptome and metabolome analysis was performed to investigate the effects of white (control), blue (B), red (R), and red/blue (60R/40B) light on blueberry growth and reveal the potential pathway controlling anthocyanin biosynthesis in blueberry leaves.

RESULTS

The anthocyanin content was significantly improved by the blue and red/blue light when compared with white light, whereas there was a significant reduction in the photosynthesis under the blue light, showing an inverse trend to that of anthocyanin accumulation. Transcriptomic analysis resulted in the assembly of 134,709 unigenes. Of these, 22 were differentially expressed genes (DEGs) that participate in the anthocyanin biosynthesis pathway, with the majority being significantly up-regulated under the blue light. Most of the photosynthesis-related genes that were down-regulated were expressed during anthocyanin accumulation. Targeted metabolome profiling identified 44 metabolites associated with anthocyanin biosynthesis. The contents of most of these metabolites were higher under blue light than the other light conditions, which was consistent with the transcriptome results. The integrated transcriptome and metabolome analysis suggested that, under blue light, leucoanthocyanidin dioxygenase (LDOX), O-methyltransferase (OMT), and UDP-glucose flavonoid glucosyltransferase (UFGT) were the most significantly expressed, and they promoted the synthesis of cyanidin (Cy), malvidin (Mv), and pelargonidin (Pg) anthocyanidins, respectively. The expression levels of dihydroflavonol 4-reductase (DFR) and OMT, as well as the accumulation of delphinidin (Dp), peonidin (Pn), and petunidin (Pt), were significantly increased by the red/blue light.

DISCUSSION

The blue and red/blue lights promoted anthocyanin biosynthesis via inducing the expression of key structural genes and accumulation of metabolites involved in anthocyanin synthesis pathway. Moreover, there was a possible feedback regulating correlation between anthocyanin biosynthesis and photosynthesis under different light qualities in blueberry leaves. This study would provide a theoretical basis for elucidating the underlying regulatory mechanism of anthocyanin biosynthesis of V. corymbosum.

Characterization of Cry2 genes (CRY2a and CRY2b) of B. napus and comparative analysis of BnCRY1 and BnCRY2a in regulating seedling photomorphogenesis

Cryptochrome 2 (CRY2) perceives blue/UV-A light and regulates photomorphogenesis in plants. However, besides Arabidopsis, CRY2 has been functionally characterized only in native species of japonica rice and tomato. In the present study, the BnCRY2a, generating a relatively longer cDNA and harboring an intron in its 5'UTR, has been characterized in detail. Western blot analysis revealed that BnCRY2a is light labile and degraded rapidly by 26S proteasome when seedlings are irradiated with blue light. For functional analysis, BnCRY2a was over-expressed in Brassica juncea, a related species more amenable to transformation. The BnCRY2a over-expression (BnCRY2a^OE) transgenics developed short hypocotyl and expanded cotyledons, accumulated more anthocyanin in light-grown seedlings, and displayed early flowering on maturity. Early flowering in BnCRY2a^OE transgenics was coupled with the up-regulation of many flowering-related genes such as FT. The present study also highlights the differential light sensitivity of cry1 and cry2 in controlling hypocotyl elongation growth in Brassica. BnCRY2a^OE seedlings developed much shorter hypocotyl under the low-intensity of blue light, while BnCRY1^OE seedling hypocotyls were shorter under the high-intensity blue light, compared to untransformed seedlings.

Identification and Analysis of Long Non-Coding RNAs Related to UV-B-Induced Anthocyanin Biosynthesis During Blood-Fleshed Peach (Prunus persica) Ripening

Blood flesh is a key fruit trait in peaches (Prunus persica) and can be attributed to the accumulation of anthocyanins. The roles of long non-coding RNAs (lncRNAs) have been highlighted by multiple studies in regulating fruit ripening, anthocyanin accumulation, and abiotic stress responses in many flowering plants. Such regulatory functions of lncRNAs in Prunus persica, nonetheless, have not been reported. In this research, we sequenced and analyzed the complete transcriptome of C3-20 (a blood-fleshed peach) fruit at four developmental stages. Analyses of the correlated genes and differentially expressed lncRNA target genes helped to forecast lncRNAs’ possible functions. The RNA-seq data were generated using high-throughput sequencing. In total, 17,456 putative lncRNAs, including 4,800 intergenic lncRNAs, 2,199 antisense lncRNAs, and 10,439 intronic lncRNAs were discovered, of which 4,871 differentially expressed lncRNAs (DE-lncRNAs) were annotated in the fruit developmental processes. The target genes of these DE-lncRNAs and their regulatory relationship identifying 21,795 cis-regulated and 18,271 trans-regulated targets of the DE-lncRNAs were in a similar way predicted by us. The enriched GO terms for the target genes included anthocyanin biosynthesis. Flavonoid biosynthesis and plant hormone signal transduction were also included in the enriched KEGG pathways. Co-expression network construction demonstrated that the highly expressed genes might co-regulate multiple other genes associated with auxin signal transduction and take effect in equal pathways. We discovered that lncRNAs, including LNC_000987, LNC_000693, LNC_001323, LNC_003610, LNC_001263, and LNC_003380, correlated with fruit that ripened and could take part in ethylene biosynthesis and metabolism and the ABA signaling pathway. Several essential transcription factors, such as ERFs, WRKY70, NAC56, and NAC72, may in a similar way regulate fruit ripening. Three DE-lncRNAs, XLOC_011933, XLOC_001865, and XLOC_042291, are involved in UV-B-induced anthocyanin biosynthesis and positively regulating UVR8 and COP10, were identified and characterized. Our discovery and characterization of XLOC_011933, XLOC_001865, and XLOC_042291 provide a more precise understanding and preliminarily establishes a theoretical framework for UV-B-induced flesh anthocyanin biosynthesis. This phenomenon might encourage more in-depth investigations to study the molecular mechanisms underlying peach flesh coloring.

The Function and Photoregulatory Mechanisms of Cryptochromes From Moso Bamboo (Phyllostachys edulis)

Light is one of the most important environmental factors affecting growth and geographic distribution of forestry plants. Moso bamboo is the largest temperate bamboo on earth and an important non-woody forestry species that serves not only important functions in the economy of rural areas but also carbon sequestration in the world. Due to its decades-long reproductive timing, the germplasm of moso bamboo cannot be readily improved by conventional breeding methods, arguing for a greater need to study the gene function and regulatory mechanisms of this species. We systematically studied the photoregulatory mechanisms of the moso bamboo (Phyllostachys edulis) cryptochrome 1, PheCRY1. Our results show that, similar to its Arabidopsis counterpart, the bamboo PheCRY1s are functionally restricted to the blue light inhibition of cell elongation without an apparent activity in promoting floral initiation. We demonstrate that PheCRY1s undergo light-dependent oligomerization that is inhibited by PheBIC1s, and light-dependent phosphorylation that is catalyzed by PhePPKs. We hypothesize that light-induced phosphorylation of PheCRY1s facilitate their degradation, which control availability of the PheCRY1 proteins and photosensitivity of bamboo plants. Our results demonstrate the evolutionary conservation of not only the function but also photoregulatory mechanism of PheCRY1 in this monocot forestry species.

Cryptochrome 2 from Lilium × formolongi Regulates Photoperiodic Flowering in Transgenic Arabidopsis thaliana

The photoperiodic flowering pathway is essential for plant reproduction. As blue and ultraviolet-A light receptors, cryptochromes play an important role in the photoperiodic regulation of flowering. Lilium × formolongi is an important cut flower that flowers within a year after seed propagation. Floral induction is highly sensitive to photoperiod. In this study, we isolated the CRYPTOCHROME2 gene (LfCRY2) from L. × formolongi. The predicted LfCRY2 protein was highly homologous to other CRY2 proteins. The transcription of LfCRY2 was induced by blue light. LfCRY2 exhibits its highest diurnal expression during the floral induction stage under both long-day and short-day photoperiods. Overexpression of LfCRY2 in Arabidopsis thaliana promoted flowering under long days but not short days, and inhibited hypocotyl elongation under blue light. Furthermore, LfCRY2 was located in the nucleus and could interact with L. × formolongi CONSTANS-like 9 (LfCOL9) and A. thaliana CRY-interacting basic-helix-loop-helix 1 (AtCIB1) in both yeast and onion cells, which supports the hypothesis that LfCRY2 hastens the floral transition via the CIB1-CO pathway in a manner similar to AtCRY2. These results provide evidence that LfCRY2 plays a vital role in promoting flowering under long days in L. × formolongi.

MdBBX21, a B-Box Protein, Positively Regulates Light-Induced Anthocyanin Accumulation in Apple Peel

The red coloration of apple (Malus × domestica Borkh.) is due to the accumulation of anthocyanins in the fruit peel. Light is essential for anthocyanin biosynthesis in apple. In this study, we performed a transcriptome sequencing (RNA-seq) analysis of apple fruit exposed to light after unbagging. The identified differentially expressed genes included MdBBX21, which is homologous to Arabidopsis BBX21, suggesting it may be involved in light-induced anthocyanin biosynthesis. Additionally, MdBBX21 was localized in the nucleus and its gene was expressed earlier than MdMYB1 in apple peel treated with light. Overexpressing MdBBX21 in Arabidopsis and apple calli under light increased anthocyanin accumulation. Dual-luciferase and yeast one-hybrid assays confirmed that MdBBX21 binds to the MdHY5, MdBBX20, and MdBBX22-1/2 promoters and induces expression. At the same time, MdHY5 can also activate the expression of MdBBX21. Furthermore, bimolecular fluorescence complementation and yeast two-hybrid assays demonstrated that MdBBX21 can interact with MdHY5. This interaction can significantly enhance MdMYB1 promoter activity. These findings clarify the molecular mechanism by which MdBBX21 positively regulates light-induced anthocyanin accumulation in apple.

Photoinactivation of the oxygen-evolving complex regulates the photosynthetic strategy of the seagrass Zostera marina

Zostera marina, a widespread seagrass, evolved from a freshwater ancestor of terrestrial monocots and successfully transitioned into a completely submerged seagrass. We found that its oxygen-evolving complex (OEC) was partially inactivated in response to light exposure, as evidenced by both the increment of the relative variable fluorescence at the K-step and the downregulation of the OEC genes and proteins. This photosynthetic regulation was further addressed at both proteome and physiology levels by an in vivo study. The unchanged content of the ΔpH sensor PsbS protein and the non-photochemical quenching induction dynamics, described by a single exponential function, verified the absence of the fast qE component. Contents and activities of chlororespiration, Mehler reaction, malic acid synthesis, and photorespiration key enzymes were not upregulated, suggesting that alternative electron flows remained unactivated. Furthermore, neither significant production of singlet oxygen nor increment of total antioxidative capacity indicated that reactive oxygen species were not produced during light exposure. In summary, these low electron consumptions may allow Z. marina to efficiently use the limited electrons caused by partial OEC photoinactivation to maintain a normal carbon assimilation level.

Anything New under the Sun? An Update on Modulation of Bioactive Compounds by Different Wavelengths in Agricultural Plants

Plants continuously rely on light as an energy source and as the driver of many processes in their lifetimes. The ability to perceive different light radiations involves several photoreceptors, which in turn activate complex signalling cascades that ultimately lead to a rearrangement in plant metabolism as an adaptation strategy towards specific light conditions. This review, after a brief summary of the structure and mode of action of the different photoreceptors, introduces the main classes of secondary metabolites and specifically focuses on the influence played by the different wavelengths on the content of these compounds in agricultural plants, because of their recognised roles as nutraceuticals.

The Photomorphogenic Transcription Factor PpHY5 Regulates Anthocyanin Accumulation in Response to UVA and UVB Irradiation

Red coloration contributes to fruit quality and is determined by anthocyanin content in peach (Prunus persica). Our previous study illustrated that anthocyanin accumulation is strongly regulated by light, and the effect of induction differs according to light quality. Here we showed that both ultraviolet-A (UVA) and ultraviolet-B (UVB) irradiation promoted anthocyanin biosynthesis in "Hujingmilu" peach fruit, and a combination of UVA and UVB had additional effects. The expression of anthocyanin biosynthesis and light signaling related genes, including transcription factor genes and light signaling elements, were induced following UV irradiation as early as 6 h post-treatment, earlier than apparent change in coloration which occurred at 72 h. To investigate the molecular mechanisms for UVA- and UVB-induced anthocyanin accumulation, the genes encoding ELONGATED HYPOCOTYL 5 (HY5), CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), Cryptochrome (CRY), and UV RESISTANCE LOCUS 8 (UVR8) in peach were isolated and characterized through functional complementation in corresponding Arabidopsis (Arabidopsis thaliana) mutants. PpHY5 and PpCOP1.1 restored hypocotyl length and anthocyanin content in Arabidopsis mutants under white light; while PpCRY1 and PpUVR8.1 restored AtHY5 expression in Arabidopsis mutants in response to UV irradiation. Arabidopsis PpHY5/hy5 transgenic lines accumulated higher amounts of anthocyanin under UV supplementation (compared with weak white light only), especially when UVA and UVB were applied together. These data indicated that PpHY5, acting as AtHY5 counterpart, was a vital regulator in UVA and UVB signaling pathway. In peach, the expression of PpHY5 was up-regulated by UVA and UVB, and PpHY5 positively regulated both its own transcription by interacting with an E-box in its own promoter, and the transcription of the downstream anthocyanin biosynthetic genes chalcone synthase 1 (PpCHS1), chalcone synthase 2 (PpCHS2), and dihydroflavonol 4-reductase (PpDFR1) as well as the transcription factor gene PpMYB10.1. In summary, functional evidence supports the role of PpHY5 in UVA and UVB light transduction pathway controlling anthocyanin biosynthesis. In peach this is via up-regulation of expression of genes encoding biosynthetic enzymes, as well as the transcription factor PpMYB10.1 and PpHY5 itself.

MdCER2 conferred to wax accumulation and increased drought tolerance in plants

Drought can activate many stress responses in plant growth and development, including the synthesis of epidermal wax and the induction of abscisic acid (ABA), and increased wax accumulation will improve plant drought resistance. Therefore, an examination of wax biosynthesis genes could help to better understand the molecular mechanism of environmental factors regulating wax biosynthesis and the wax associated stress response. Here, we identified the MdCER2 gene from the 'Gala' (Malus× domestica Borkh.) variety of domestic apple, which is a homolog of Arabidopsis AtCER2. It possesses a transferase domain and the protein localizes on the cell membrane. The MdCER2 gene was constitutively expressed in apple tissues and was induced by drought treatment. Finally, we transformed the MdCER2 gene into Arabidopsis to identify its function, and found ectopic expression of MdCER2 promoted accumulation of cuticular wax in both leaves and stems, decreased water loss and permeability in leaves, increased lateral root number, changed plant ABA sensitivity, and increased drought resistance.

Effect of Orchard Management Factors on Flesh Color of Two Red-Fleshed Apple Clones

Little is known about factors affecting anthocyanin biosynthesis in red-fleshed apples (Malus × domestica Borkh.). The objective was to establish the effects of orchard management factors on flesh anthocyanin content of dark-colored (DC) and light-colored (LC) apple clones. Flesh color was assessed by measuring color in the L, a, b mode using a spectrophotometer and predicting the anthocyanin content based on relationships between the absorption of a flesh extract at 530 nm and the L-value determined using a spectrophotometer (r2 = 0.99 ***). Fruit from the DC clone were red by 86 days after full bloom (DAFB), whereas the LC clone began to color at 136 DAFB. Color intensity in both clones decreased from the top of the tree to the base. Further, the intensity of the flesh color of the DC clone decreased with shading (94% absorption of incident photosynthetic active radiation). Covering a fruit with a UV absorbing film (100% UV absorption) had no effect on flesh color in the DC clone but decreased color in the LC clone. Fruit thinning increased color in DC and LC fruit. There was little change in flesh color during storage. However, the DC clone developed severe flesh browning as storage progressed beyond 30 days. The results demonstrated that light (visible and UV wavelength) stimulated, whereas shade inhibited, anthocyanin biosynthesis in the flesh under orchard conditions.

MdMYBDL1 employed by MdHY5 increases anthocyanin accumulation via repression of MdMYB16/308 in apple

Light is an important environmental factor affecting plant growth and development. Additionally, HY5 is a central factor that coordinates light signal transduction and regulates the expression of flower color-related genes. However, there are few reports describing the co-regulation of apple fruit coloration by MdHY5 and MYB transcription factors. In this study, we detected a light-inducible gene, MdMYBDL1, which encodes a MYB-like domain and is homologous to AtMYBD in Arabidopsis thaliana. Moreover, we observed that MdHY5 binds to the G-box element of the MdMYBDL1 promoter to upregulate expression. The overexpression of MdMYBDL1 enhanced anthocyanin accumulation in apple calli and inhibited the expression of MdMYB16 and its homolog, MdMYB308. Furthermore, MdMYB16 can form a dimer with MdMYB308 and functions as a negative regulator of anthocyanin biosynthesis. Interestingly, MdMYB16 and MdMYB308 promoter activities were inhibited by MdMYBDL1 and MdHY5. These findings imply that MdHY5 responds to light signals and functions upstream of different types of MYB transcription factors, ultimately regulating anthocyanin accumulation in apples.

ClCRY2 facilitates floral transition in Chrysanthemum lavandulifolium by affecting the transcription of circadian clock-related genes under short-day photoperiods

Plants sense photoperiod signals to confirm the optimal flowering time. Previous studies have shown that Cryptochrome2 (CRY2) functions to promote floral transition in the long-day plant (LDP) Arabidopsis; however, the function and molecular mechanism by which CRY2 regulates floral transition in short-day plants (SDPs) is still unclear. In this study, we identified a CRY2 homologous gene, ClCRY2, from Chrysanthemum lavandulifolium, a typical SDP. The morphological changes in the C. lavandulifolium shoot apex and ClFTs expression analysis under SD conditions showed that adult C. lavandulifolium completed the developmental transition from vegetative growth to reproductive growth after eight SDs. Meanwhile, ClCRY2 mRNA exhibited an increasing trend from 0 to 8 d of SD treatment. ClCRY2 overexpression in wild-type (WT) Arabidopsis and C. lavandulifolium resulted in early flowering. The transcript levels of the CONSTANS-like (COL) genes ClCOL1, ClCOL4, and ClCOL5, and FLOWERING LOCUS T (FT) homologous gene ClFT1 were upregulated in ClCRY2 overexpression (ClCRY2-OE) C. lavandulifolium under SD conditions. The transcript levels of some circadian clock-related genes, including PSEUDO-REPONSE REGULATOR 5 (PRR5), ZEITLUPE (ZTL), FLAVIN-BINDING KELCH REPEAT F-BOX 1 (FKF1), and GIGANTEA (GI-1 and GI-2), were upregulated in ClCRY2-OE C. lavandulifolium, while the expression levels of other circadian clock-related genes, such as EARLY FLOWERING 3 (ELF3), ELF4, LATE ELONGATED HYPOCOTYL (LHY), PRR73, and REVEILLE8 (RVE8), were downregulated in ClCRY2-OE C. lavandulifolium under SD conditions. Taken together, the results suggest that ClCRY2 promotes floral transition by fine-tuning the expression of circadian clock-related gene, ClCOLs and ClFT1 in C. lavandulifolium under SD conditions.

The blue light signal transduction pathway is involved in anthocyanin accumulation in 'Red Zaosu' pear

MAIN CONCLUSION

A conserved blue light sensing and transduction pathway contributes to blue light-induced anthocyanin accumulation in the peel of red pear. Peel color is an economically important characteristic that influences the appearance quality of red pear, whose red color is due to anthocyanin accumulation. The process of coloration in the fruit peel is strongly influenced by light. However, how light quality influences color development remains unclear. In this study, we analyzed the effects of different light qualities on color development in the red pear 'Red Zaosu', a mutant of the hybrid cultivar 'Zaosu' of Pyrus pyrifolia and P. communis. The results showed that blue light increased anthocyanin accumulation after 72 h of light treatment, while red light had almost no effect. The expression of anthocyanin biosynthesis-related genes showed a similar trend to the anthocyanin accumulation. To clarify the mechanism of blue-light induced coloration, PpCRYs, PpCOP1 and PpHY5 genes were cloned. Gene expression analysis showed that their transcript abundance did not correlate with the expression of anthocyanin-related genes or anthocyanin content, but the yeast two-hybrid system revealed conserved physical interactions among these proteins. In addition, PpHY5 directly bound to the promoters of the anthocyanin biosynthesis genes PpCHS, PpDFR, PpANS and PpMYB10, and activated the transcription of PpCHS in a Nicotiana benthamiana-based dual-luciferase assay. In summary, our results preliminarily revealed that the conserved blue light signal transduction module CRY-COP1-HY5 contributed to the anthocyanin biosynthesis induced by blue light in red pear. However, our results did not provide evidence for why red light had no effect on anthocyanin accumulation, which needs further study.

Overexpression of sweet sorghum cryptochrome 1a confers hypersensitivity to blue light, abscisic acid and salinity in Arabidopsis

This work provides the bioinformatics, expression pattern and functional analyses of cryptochrome 1a from sweet sorghum (SbCRY1a), together with an exploration of the signaling mechanism mediated by SbCRY1a. Sweet sorghum [Sorghum bicolor (L.) Moench] is considered to be an ideal candidate for biofuel production due to its high efficiency of photosynthesis and the ability to maintain yield under harsh environmental conditions. Blue light receptor cryptochromes regulate multiple aspects of plant growth and development. Here, we reported the function and signal mechanism of sweet sorghum cryptochrome 1a (SbCRY1a) to explore its potential for genetic improvement of sweet sorghum varieties. SbCRY1a transcripts experienced almost 24 h diurnal cycling; however, its protein abundance showed no oscillation. Overexpression of SbCRY1a in Arabidopsis rescued the phenotype of cry1 mutant in a blue light-specific manner and regulated HY5 accumulation under blue light. SbCRY1a protein was present in both nucleus and cytoplasm. The photoexcited SbCRY1a interacted directly with a putative RING E3 ubiquitin ligase constitutive photomorphogenesis 1 (COP1) from sweet sorghum (SbCOP1) instead of SbSPA1 to suppress SbCOP1-SbHY5 interaction responding to blue light. These observations indicate that the function and signaling mechanism of cryptochromes are basically conservative between monocotyledons and dicotyledons. Moreover, SbCRY1a-overexpressed transgenic Arabidopsis showed oversensitive to abscisic acid (ABA) and salinity. The ABA-responsive gene ABI5 was up-regulated evidently in SbCRY1a transgenic lines, suggesting that SbCRY1a might regulate ABA signaling through the HY5-ABI5 regulon.

Differential Sensitivity of Fruit Pigmentation to Ultraviolet Light between Two Peach Cultivars

Anthocyanins provide nutritional benefits and are responsible for red coloration in many fruits. Light affects anthocyanin biosynthesis in peach (Prunus persica). However, some cultivars show differential sensitivity to light. In the present study, 'Hujingmilu (HJ),' a naturally deeply colored cultivar, and 'Yulu (YL),' showing low pigmentation, were used to study the mechanism underlying UV-light-induced anthocyanin biosynthesis. Both UVA and UVB induced fruit pigmentation of 'HJ,' but 'YL' was only sensitive to UVB. Transcriptomic analyses showed over 5000 genes were differentially expressed by pairwise comparisons of RNA libraries isolated from tissue of each cultivar treated with darkness, UVA and UVB. Twenty-three genes related to anthocyanin biosynthesis were identified from the transcriptome data, which were coordinately up-regulated during accumulation of anthocyanins, and down-regulated in the dark. Altered expression of several light receptors, as well as CONSTITUTIVE PHOTOMORPHOGENIC10 (COP10) and ELONGATED HYPOCOTYL 5 homolog (HYH), and a specific anthocyanin transporter glutathione S-transferase (GST), in 'YL' fruit appears to be responsible for the insensitivity to UVA of this cultivar. Expression profiles of several transcription factors of the families MYB, bHLH, bZIP and NAC were highly correlated with those of the anthocyanin biosynthesis genes. The study provides a valuable overview of the underlying molecular mechanisms of UV-light induced anthocyanin response using peach cultivars with differing light sensitivities.

Transcriptome Analysis Identifies Key Candidate Genes Mediating Purple Ovary Coloration in Asiatic Hybrid Lilies

Lily tepals have a short lifespan. Once the tepals senesce, the ornamental value of the flower is lost. Some cultivars have attractive purple ovaries and fruits which greatly enhance the ornamental value of Asiatic hybrid lilies. However, little is known about the molecular mechanisms of anthocyanin biosynthesis in Asiatic hybrid lily ovaries. To investigate the transcriptional network that governs purple ovary coloration in Asiatic hybrid lilies, we obtained transcriptome data from green ovaries (S1) and purple ovaries (S2) of Asiatic "Tiny Padhye". Comparative transcriptome analysis revealed 4228 differentially expressed genes. Differential expression analysis revealed that ten unigenes including four CHS genes, one CHI gene, one F3H gene, one F3'H gene, one DFR gene, one UFGT gene, and one 3RT gene were significantly up-regulated in purple ovaries. One MYB gene, LhMYB12-Lat, was identified as a key transcription factor determining the distribution of anthocyanins in Asiatic hybrid lily ovaries. Further qPCR results showed unigenes related to anthocyanin biosynthesis were highly expressed in purple ovaries of three purple-ovaried Asiatic hybrid lilies at stages 2 and 3, while they showed an extremely low level of expression in ovaries of three green-ovaried Asiatic hybrid lilies during all developmental stages. In addition, shading treatment significantly decreased pigment accumulation by suppressing the expression of several unigenes related to anthocyanin biosynthesis in ovaries of Asiatic "Tiny Padhye". Lastly, a total of 15,048 Simple Sequence Repeats (SSRs) were identified in 13,710 sequences, and primer pairs for SSRs were designed. The results could further our understanding of the molecular mechanisms of anthocyanin biosynthesis in Asiatic hybrid lily ovaries.

Novel insight into the mechanism underlying light-controlled anthocyanin accumulation in eggplant (Solanum melongena L.)

Eggplant is rich in anthocyanins, which are the major secondary metabolites and beneficial to human health. We discovered that the anthocyanin biosynthesis of eggplant cultivar 'Lanshan Hexian' was regulated by light. In this study, we isolated two blue light receptor genes, SmCRY1 and SmCRY2, and negative/positive anthocyanin regulatory factors SmCOP1 and SmHY5 from eggplant. In terms of transcript levels, SmCRY1, SmCRY2 and SmHY5 were up-regulated by light, while SmCOP1 was down-regulated. Subsequently, the four genes were functionally complemented in phenotype of corresponding mutants, indicating that they act as counterparts of Arabidopsis genes. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that SmCRY1 and SmCRY2 interact with SmCOP1 in a blue-light-dependent manner. It also obtained the result that SmCOP1 interacts with SmHY5 and SmMYB1. Furthermore, using yeast one-hybrid assay, we found that SmHY5 and SmMYB1 both bind the promoters of anthocyanin biosynthesis structural genes (SmCHS and SmDFR). Taken together, blue-light-triggered CRY1/CRY2-COP1 interaction creates the condition that HY5 and MYB1 combine with the downstream anthocyanin synthesis genes (CHS and DFR) in eggplant. Our finding provides a new working model by which light controls anthocyanin accumulation in eggplant.

Molecular Cloning and Functional Analysis of UV RESISTANCE LOCUS 8 (PeUVR8) from Populus euphratica

Ultraviolet-B (UV-B; 280–315 nm) light, which is an integral part of the solar radiation reaching the surface of the Earth, induces a broad range of physiological responses in plants. The UV RESISTANCE LOCUS 8 (UVR8) protein is the first and only light photoreceptor characterized to date that is specific for UV-B light and it regulates various aspects of plant growth and development in response to UV-B light. Despite its involvement in the control of important plant traits, most studies on UV-B photoreceptors have focused on Arabidopsis and no data on UVR8 function are available for forest trees. In this study, we isolated a homologue of the UV receptor UVR8 of Arabidopsis, PeUVR8, from Populus euphratica (Euphrates poplar) and analyzed its structure and function in detail. The deduced PeUVR8 amino acid sequence contained nine well-conserved regulator of chromosome condensation 1 (RCC1) repeats and the region 27 amino acids from the C terminus (C27) that interact with COP1 (CONSTITUTIVELY PHOTOMORPHOGENIC1). Secondary and tertiary structure analysis showed that PeUVR8 shares high similarity with the AtUVR8 protein from Arabidopsis thaliana. Using heterologous expression in Arabidopsis, we showed that PeUVR8 overexpression rescued the uvr8 mutant phenotype. In addition, PeUVR8 overexpression in wild-type background seedlings grown under UV-B light inhibited hypocotyl elongation and enhanced anthocyanin accumulation. Furthermore, we examined the interaction between PeUVR8 and AtCOP1 using a bimolecular fluorescence complementation (BiFC) assay. Our data provide evidence that PeUVR8 plays important roles in the control of photomorphogenesis in planta.

Light and abscisic acid independently regulated FaMYB10 in Fragaria × ananassa fruit

Light and ABA independently regulated anthocyanin biosynthesis via activation of FaMYB10 expression. FaMYB10 accelerated anthocyanin synthesis of pelargonidin 3-glucoside and cyanidin 3-glucoside during strawberry fruit ripening. Light is an integral factor in fruit ripening. Ripening in non-climacteric fruit is also effected by the plant hormone abscisic acid (ABA). However, how light and/or ABA regulate fruit ripening processes, such as strawberry color development remains elusive. Results of the present study showed light and ABA regulated strawberry fruit coloration via activation of FaMYB10 expression, an R2R3 MYB transcription factor. Light exposure increased FaMYB10 transcript levels, flavonoid pathway genes, and anthocyanin content. Exogenous ABA promoted FaMYB10 expression, and anthocyanin content, accompanied by increased ABA-responsive transcript levels and flavonoid pathway genes. ABA biosynthesis inhibitor treatment, and RNAi-mediated down-regulation of the ABA biosynthetic gene (9-cis epoxycarotenoid dioxygenase: FaNCED1), and ABA receptor (magnesium chelatase H subunit: FaCHLH/ABAR) showed inverse ABA effects. Furthermore, additive effects were observed in anthocyanin accumulation under combined light and ABA, indicating independent light and ABA signaling pathways. FaMYB10 down-regulation by Agrobacterium-mediated RNA interference (RNAi) in strawberry fruits showed decreased pelargonidin 3-glucoside and cyanidin 3-glucoside levels, accompanied by consistent flavonoid pathway gene expression levels. FaMYB10 over-expression showed opposite FaMYB10 RNAi phenotypes, particularly cyanidin 3-glucoside synthesis by FaMYB10, which was correlated with FaF3'H transcript levels. These data provided evidence that light and ABA promoted FaMYB10 expression, resulting in anthocyanin accumulation via acceleration of flavonoid pathway gene expression. Finally, our results suggested FaMYB10 serves a role as a signal transduction mediator from light and ABA perception to anthocyanin synthesis in strawberry fruit.

Fruit-localized photoreceptors increase phenolic compounds in berry skins of field-grown Vitis vinifera L. cv. Malbec

Sunlight exposure has multiple effect on fruits, as it affects the light climate perceived by fruit photoreceptors and fruit tissue temperature. In grapes (Vitis vinifera L.), light exposure can have a strong effect on fruit quality and commercial value; however, the mechanisms of light action are not well understood. The role of fruit-localized photoreceptors in the control of berry quality traits was evaluated under field conditions in a commercial vineyard in Mendoza (Argentina). Characterization of the diurnal dynamics of the fruit light environment in a vertical trellis system indicated that clusters were shaded by leaves during most of the photoperiod. Supplementation of the fruit light environment from 20 days before veraison until technological harvest showed that red (R, 660 nm) and blue (B, 470 nm) light strongly increased total phenolic compound levels at harvest in the berry skins without affecting sugar content, acidity or berry size. Far-red (FR, 730 nm) and green (G, 560 nm) light supplementation had relatively small effects. The stimulation of berry phytochromes and cryptochromes favored accumulation of flavonoid and non-flavonoid compounds, including anthocyanins, flavonols, flavanols, phenolic acids and stilbenes. These results demonstrate that the chemical composition of grape berries is modulated by the light quality received by the clusters under field conditions, and that fruit photoreceptors are not saturated even in areas of high insolation and under management systems that are considered to result in a relatively high exposure of fruits to solar radiation. Therefore, manipulation of the light environment or the light sensitivity of fruits could have significant effects on critical grape quality traits.

Cloning of the cryptochrome-encoding PeCRY1 gene from Populus euphratica and functional analysis in Arabidopsis

Cryptochromes are photolyase-like blue/UV-A light receptors that evolved from photolyases. In plants, cryptochromes regulate various aspects of plant growth and development. Despite of their involvement in the control of important plant traits, however, most studies on cryptochromes have focused on lower plants and herbaceous crops, and no data on cryptochrome function are available for forest trees. In this study, we isolated a cryptochrome gene, PeCRY1, from Euphrates poplar (Populus euphratica), and analyzed its structure and function in detail. The deduced PeCRY1 amino acid sequence contained a conserved N-terminal photolyase-homologous region (PHR) domain as well as a C-terminal DQXVP-acidic-STAES (DAS) domain. Secondary and tertiary structure analysis showed that PeCRY1 shares high similarity with AtCRY1 from Arabidopsis thaliana. PeCRY1 expression was upregulated at the mRNA level by light. Using heterologous expression in Arabidopsis, we showed that PeCRY1 overexpression rescued the cry1 mutant phenotype. In addition, PeCRY1 overexpression inhibited hypocotyl elongation, promoted root growth, and enhanced anthocyanin accumulation in wild-type background seedlings grown under blue light. Furthermore, we examined the interaction between PeCRY1 and AtCOP1 using a bimolecular fluorescence complementation (BiFc) assay. Our data provide evidence for the involvement of PeCRY1 in the control of photomorphogenesis in poplar.

Reactive oxygen species produced via plasma membrane NADPH oxidase regulate anthocyanin synthesis in apple peel

Solar ultraviolet irradiation regulates anthocyanin synthesis in apple peel by modulating the production of reactive oxygen species via plasma membrane NADPH oxidase instead of other pathways. The synthesis of anthocyanin in apple peels is dependent upon solar irradiation. Using 3-mm commercial glass to attenuate solar UV-A and UV-B light, we confirmed that solar UV irradiation regulated anthocyanin synthesis in apple peels after exposing previously bagged fruit to sunlight. During sunlight exposure, UV attenuation did not affect the expression of MdHY5, MdCOP1, or MdCRY2, but significantly lowered plasma membrane NADPH oxidase activity and superoxide anion concentrations. UV attenuation also reduced the expression levels of MdMYB10, MdPAL, MdCHS, MdF3H, MdDFR, MdANS and MdUFGT1, UDP-glycose:flavonoid 3-O-glycosyltransferase (UFGT) activity, and local concentrations of anthocyanin and quercetin-3-glycoside. In contrast, exogenous application of hydrogen peroxide could enhance anthocyanin and quercetin-3-glycoside synthesis. Xanthophyll cycle pool size on a chlorophyll basis was higher but its de-epoxidation was lower under direct sunlight irradiation than that under UV-attenuating conditions. This suggests that reactive oxygen species (ROS) produced in chloroplast are not major contributors to anthocyanin synthesis regulation. Inhibition of plasma membrane NADPH oxidase activity lowered the production of ROS through this mechanism, significantly inhibited the synthesis of anthocyanin, and increased the total production of ROS in apple peel under direct sunlight irradiation, suggesting that ROS produced via plasma membrane NADPH oxidase regulates anthocyanin synthesis. In summary, solar UV irradiation regulated anthocyanin synthesis in apple peels by modulating the production of ROS via plasma membrane NADPH oxidase.

New insights into the regulation of anthocyanin biosynthesis in fruits

Anthocyanins are important health-promoting pigments that make a major contribution to the quality of fruits. The biosynthetic pathway leading to anthocyanins is well known and the key regulatory genes controlling the pathway have been isolated in many species. Recently, a considerable amount of new information has been gathered on the developmental and environmental regulation of anthocyanin biosynthesis in fruits, specifically the impact of regulation through light. New discoveries have begun to reveal links between the developmental regulatory network and the specific regulators of anthocyanin biosynthesis during fruit ripening. In this opinion article, a simplified model for the different regulatory networks involved with anthocyanin production in fruit is proposed.