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

Growth, phytochemical, and phytohormonal responses of basil to different light durations and intensities under constant daily light integral

Horticulture in controlled environments has been increasingly used to tackle limitations on crop production. As a crucial environmental factor, light regulate plant growth and metabolism. In the present study, basil plants were subjected to different light durations and intensities considering constant daily light integral (DLI). The lighting environment included 200, 300, and 400 µmol m- 2 s- 1 intensities for 18, 12, and 9 h, respectively. DLI amounted to 12.96 mol m- 2 d- 1 among all light treatments (LI200 for 18 h, LI300 for 12 h, and LI400 for 9 h). Half of the plants under each light treatment were exposed to 30 µmol m- 2 s- 1 of far-red light. The results indicated the general negative impact of LI400/9 on the growth of basils. Exposure to far-red light hurt the growth of the shoot, while it enhanced stem and petiole elongation. This effect was due to higher gibberellin accumulation, which resulted in shade avoidance responses. Exposure to far-red light also reduced anthocyanin and flavonoid contents, as two important nutritional components. Soluble carbohydrates increased, while storage carbohydrates decreased by increasing lighting duration/decreasing light intensity or by far-red light inclusion. The lowest antioxidant activity was detected in LI400/9. In the LI200/18, the highest level of auxin and the lowest level of cytokinin were detected, while the LI300/12 exhibited the highest level of gibberellin hormone. Low light intensity and long photoperiod enhanced plant biomass and phytochemical production and are recommended for basil production in controlled environments.

PpBBX32 and PpZAT5 modulate temperature-dependent and tissue-specific anthocyanin accumulation in peach fruit

Anthocyanins are important compounds for fruit quality and nutrition. The R2R3 MYB transcription factor PpMYB10.1 is known to be critical for regulating anthocyanin accumulation in peach. However, regulatory factors upstream of PpMYB10.1 which control temperature-dependent, cultivar-contrasted and tissue-specific anthocyanin accumulation remain to be determined. In this study, differential anthocyanin accumulation in the outer flesh near the peel (OF) of peach [Prunus persica (L.) Batsch] was observed between cultivars 'Zhonghuashoutao' and 'Dongxuemi', as well as among different storage temperatures and different fruit tissues of 'Zhonghuashoutao'. By cross-comparisons of RNA-Seq data of samples with differential anthocyanin accumulation, transcription factor genes PpBBX32 and PpZAT5 were identified. These were functionally characterized as two positive regulators for anthocyanin accumulation via transient expression and genetic transformation. Various interaction assays revealed that both PpBBX32 and PpZAT5 can directly activate the PpMYB10.1 promoter and meanwhile interact at protein level as a PpZAT5-PpBBX32-PpMYB10.1 complex. Furthermore, the results of in silico analysis and exogenous application of methyl jasmonate (MeJA) indicated that MeJA favored anthocyanin accumulation, while it was also found that anthocyanin accumulation as well as PpBBX32 and PpZAT5 expression correlated significantly with endogenous JA and JA-Ile in different fruit tissues. In summary, PpBBX32 and PpZAT5 are upstream activators of PpMYB10.1, allowing JAs to take part in temperature-dependent and tissue-specific anthocyanin accumulation by modulating their expression. This work enriches the knowledge of the transcriptional regulatory mechanisms for differential anthocyanin accumulation under internal and external factors.

Supplementing with monochromatic blue LED light during the day, rather than at night, increases anthocyanins in the berry skin of grapevine (Vitis vinifera L.)

MAIN CONCLUSION

Supplying monochromatic blue LED light during the day, but not at night, promotes early coloration and improves anthocyanin accumulation in the skin of grape berries. Specific light spectra, such as blue light, are known to promote the biosynthesis and accumulation of anthocyanins in fruit skins. However, research is scarce on whether supplement of blue light during different periods of one day can differ in their effect. Here, we compared the consequences of supplying blue light during the day and night on the accumulation of anthocyanins in pigmented grapevine (Vitis vinifera) berries. Two treatments of supplemented monochromatic blue light were tested, with light emitting diodes (LED) disposed close to the fruit zone, irradiating between 8:00 and 18:00 (Dayblue) or between 20:00 and 6:00 (Nightblue). Under the Dayblue treatment, berry coloration was accelerated and total anthocyanins in berry skins increased faster than the control (CK) and also when compared to the Nightblue condition. In fact, total anthocyanin content was similar between CK and Nightblue. qRT-PCR analysis indicated that Dayblue slightly improved the relative expression of the anthocyanin-structural gene UFGT and its regulator MYBA1. Instead, the expression of the light-reception and -signaling related genes CRY, HY5, HYH, and COP1 rapidly increased under Dayblue. This study provides insights into the effect of supplementing monochromatic LED blue light during the different periods of one day, on anthocyanins accumulation in the berry skin.

DNA methylation controlling abscisic acid catabolism responds to light to mediate strawberry fruit ripening

Phytohormones, epigenetic regulation and environmental factors regulate fruit ripening but their interplay during strawberry fruit ripening remains to be determined. In this study, bagged strawberry fruit exhibited delayed ripening compared with fruit grown in normal light, correlating with reduced abscisic acid (ABA) accumulation. Transcription of the key ABA catabolism gene, ABA 8'-hydroxylase FaCYP707A4, was induced in bagged fruit. With light exclusion whole genome DNA methylation levels were up-regulated, corresponding to a delayed ripening process, while DNA methylation levels in the promoter of FaCYP707A4 were suppressed, correlating with increases in transcript and decreased ABA content. Experiments indicated FaCRY1, a blue light receptor repressed in bagged fruit and FaAGO4, a key protein involved in RNA-directed DNA methylation, could bind to the promoter of FaCYP707A4. The interaction between FaCRY1 and FaAGO4, and an increased enrichment of FaAGO4 directed to the FaCYP707A4 promoter in fruit grown under light suggests FaCRY1 may influence FaAGO4 to modulate the DNA methylation status of the FaCYP707A4 promoter. Furthermore, transient overexpression of FaCRY1, or an increase in FaCRY1 transcription by blue light treatment, increases the methylation level of the FaCYP707A4 promoter, while transient RNA interference of FaCRY1 displayed opposite phenotypes. These findings reveal a mechanism by which DNA methylation influences ABA catabolism, and participates in light-mediated strawberry ripening.

A distinct foliar pigmentation pattern formed by activator-repressor gradients upstream of an anthocyanin-activating R2R3-MYB

The emergence of novel traits is often preceded by a potentiation phase, when all the genetic components necessary for producing the trait are assembled. However, elucidating these potentiating factors is challenging. We have previously shown that an anthocyanin-activating R2R3-MYB, STRIPY, triggers the emergence of a distinct foliar pigmentation pattern in the monkeyflower Mimulus verbenaceus. Here, using forward and reverse genetics approaches, we identify three potentiating factors that pattern STRIPY expression: MvHY5, a master regulator of light signaling that activates STRIPY and is expressed throughout the leaf, and two leaf developmental regulators, MvALOG1 and MvTCP5, that are expressed in opposing gradients along the leaf proximodistal axis and negatively regulate STRIPY. These results provide strong empirical evidence that phenotypic novelties can be potentiated through incorporation into preexisting genetic regulatory networks and highlight the importance of positional information in patterning the novel foliar stripe.

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.

Screening and verification of proteins that interact with the anthocyanin-related transcription factor PbrMYB114 in 'Yuluxiang' pear

Despite extensive research highlighting the pivotal role of MYB transcription factors in regulating anthocyanin biosynthesis, the interactive regulatory network involving these MYB factors in pear fruits remains inadequately characterized. In this study, the anthocyanin-regulatory gene PbrMYB114 was successfully cloned from 'Yuluxiang' pear (Pyrus bretschneideri) fruits, and its influence on anthocyanin accumulation was confirmed through transient expression assays. Specifically, the co-transformation of PbrMYB114 with its partner PbrbHLH3 in pears served to validate the functional role of PbrMYB114. Subsequently, PbrMYB114 was employed as bait in a yeast two-hybrid screening assay, using a 'Yuluxiang' pear protein library, which led to the identification of 25 interacting proteins. Further validation of the interactions between PbrMYB114 and PbrMT2/PbrMT3 was conducted. Investigations into the role of PbrMT2 and PbrMT3 in 'Duli' seedlings (Pyrus betulaefolia) revealed their potential to enhance anthocyanin accumulation. The outcomes of these studies provide novel insights into the protein network that regulates pear anthocyanin biosynthesis, particularly the functional interactions among PbrMYB114 and associated proteins.

The Effect of Combined Elicitation with Light and Temperature on the Chlorogenic Acid Content, Total Phenolic Content and Antioxidant Activity of Berula erecta in Tissue Culture

Chlorogenic acid is one of the most prominent bioactive phenolic acids with great pharmacological, cosmetic and nutritional value. The potential of Berula erecta in tissue culture was investigated for the production of chlorogenic acid and its elicitation combined with light of different wavelengths and low temperature. The content of chlorogenic acid in the samples was determined by HPLC-UV, while the content of total phenolic compounds and the antioxidant activity of their ethanol extracts were evaluated spectrophotometrically. The highest fresh and dry biomasses were obtained in plants grown at 23 °C. This is the first study in which chlorogenic acid has been identified and quantified in Berula erecta. The highest chlorogenic acid content was 4.049 mg/g DW. It was determined in a culture grown for 28 days after the beginning of the experiment at 12 °C and under blue light. The latter also contained the highest content of total phenolic compounds, and its extracts showed the highest antioxidant activity. Berula erecta could, potentially, be suitable for the in vitro production of chlorogenic acid, although many other studies should be conducted before implementation on an industrial scale.

For a Colorful Life: Recent Advances in Anthocyanin Biosynthesis during Leaf Senescence

Leaf senescence is the last stage of leaf development, and it is accompanied by a leaf color change. In some species, anthocyanins are accumulated during leaf senescence, which are vital indicators for both ornamental and commercial value. Therefore, it is essential to understand the molecular mechanism of anthocyanin accumulation during leaf senescence, which would provide new insight into autumn coloration and molecular breeding for more colorful plants. Anthocyanin accumulation is a surprisingly complex process, and significant advances have been made in the past decades. In this review, we focused on leaf coloration during senescence. We emphatically discussed several networks linked to genetic, hormonal, environmental, and nutritional factors in regulating anthocyanin accumulation during leaf senescence. This paper aims to provide a regulatory model for leaf coloration and to put forward some prospects for future development.

Integrated transcriptome and metabolome analysis reveals anthocyanin biosynthesis mechanisms in pepper (Capsicum annuum L.) leaves under continuous blue light irradiation

BACKGROUND

Different metabolic compounds give pepper leaves and fruits their diverse colors. Anthocyanin accumulation is the main cause of the purple color of pepper leaves. The light environment is a critical factor affecting anthocyanin biosynthesis. It is essential that we understand how to use light to regulate anthocyanin biosynthesis in plants.

RESULT

Pepper leaves were significantly blue-purple only in continuous blue light or white light (with a blue light component) irradiation treatments, and the anthocyanin content of pepper leaves increased significantly after continuous blue light irradiation. This green-to-purple phenotype change in pepper leaves was due to the expression of different genes. We found that the anthocyanin synthesis precursor-related genes PAL and 4CL, as well as the structural genes F3H, DFR, ANS, BZ1, and F3'5'H in the anthocyanin synthesis pathway, had high expression under continuous blue light irradiation. Similarly, the expression of transcription factors MYB1R1-like, MYB48, MYB4-like isoform X1, bHLH143-like, and bHLH92-like isoform X3, and circadian rhythm-related genes LHY and COP1, were significantly increased after continuous blue light irradiation. A correlation network analysis revealed that these transcription factors and circadian rhythm-related genes were positively correlated with structural genes in the anthocyanin synthesis pathway. Metabolomic analysis showed that delphinidin-3-O-glucoside and delphinidin-3-O-rutinoside were significantly higher under continuous blue light irradiation relative to other light treatments. We selected 12 genes involved in anthocyanin synthesis in pepper leaves for qRT-PCR analysis, and the accuracy of the RNA-seq results was confirmed.

CONCLUSIONS

In this study, we found that blue light and 24-hour irradiation together induced the expression of key genes and the accumulation of metabolites in the anthocyanin synthesis pathway, thus promoting anthocyanin biosynthesis in pepper leaves. These results provide a basis for future study of the mechanisms of light quality and photoperiod in anthocyanin synthesis and metabolism, and our study may serve as a valuable reference for screening light ratios that regulate anthocyanin biosynthesis in plants.

Eggplant transcription factor SmMYB5 integrates jasmonate and light signaling during anthocyanin biosynthesis

Low light conditions severely suppress anthocyanin synthesis in fruit skins, leading to compromised fruit quality in eggplant (Solanum melongena L.) production. In this study, we found that exogenous methyl-jasmonate (MeJA) application can effectively rescue the poor coloration of the eggplant pericarp under low light conditions. However, the regulatory relationship between jasmonate and light signaling for regulating anthocyanin synthesis remains unclear. Here, we identified a JA response factor, SmMYB5, as an anthocyanin positive regulator by applying RNA-sequencing and characterization of transgenic plants. Firstly, we resolved that SmMYB5 can interact with TRANSPARENT TESTA8 (SmTT8), an anthocyanin-promoted BASIC HELIX-LOOP-HELIX (bHLH) transcription factor, to form the SmMYB5-SmTT8 complex and activate CHALCONE SYNTHASE (SmCHS), FLAVANONE-3-HYDROXYLASE (SmF3H), and ANTHOCYANIN SYNTHASE (SmANS) promoters by direct binding. Secondly, we revealed that JA signaling repressors JASMONATE ZIM DOMAIN5 (SmJAZ5) and SmJAZ10 can interfere with the stability and transcriptional activity of SmMYB5-SmTT8 by interacting with SmMYB5. JA can partially rescue the transcriptional activation of SmF3H and SmANS promoters by inducing SmJAZ5/10 degradation. Thirdly, we demonstrated that the protein abundance of SmMYB5 is regulated by light. CONSTITUTIVELY PHOTOMORPHOGENIC1 (SmCOP1) interacts with SmMYB5 to trigger SmMYB5 degradation via the 26S proteasome pathway. Finally, we delineated a light-dependent JA-SmMYB5 signaling pathway that promotes anthocyanin synthesis in eggplant fruit skins. These results provide insights into the mechanism of the integration of JA and light signals in regulating secondary metabolite synthesis in plants.

Screening and identification of photoresponse factors in kiwifruit (Actinidia arguta) development

BACKGROUND

Light is essential for kiwifruit development, in which photoresponse factors contributes greatly to the quality formation. 'Light sensitive hypocotyls, also known as light-dependent short hypocotyls' (LSH) gene family can participate in fruit development as photoresponse factor. However, the key LSH gene that determine kiwifruit development remains unclear. This study aim to screen and identify the key gene AaLSH9 in A. arguta.

MATERIALS AND METHODS

Genome-wide identification of the LSH gene family was used to analyse LSH genes in kiwifruit. Homologous cloning was used to confirm the sequence of candidate LSH genes. qRT-PCR and cluster analysis of expression pattern were used to screen the key AaLSH9 gene. Subcellular localization of AaLSH9 in tobacco leaves and overexpression of AaLSH9 in Arabidopsis thaliana hy5 mutant plants were used to define the acting place in cell and identify molecular function, respectively.

RESULTS

We identified 15 LSH genes, which were divided into two sub-families namely A and B. Domain analysis of A and B showed that they contained different domain organizations, which possibly played key roles in the evolution process. Three LSH genes, AaLSH2, AaLSH9, and AaLSH11, were successfully isolated from Actinidia arguta. The expression pattern and cluster analysis of these three AaLSH genes suggested AaLSH9 might be a key photoresponse gene participating in fruit development in A. arguta. Subcellular localization showed AaLSH9 protein was located in the nucleus. The overexpression of AaLSH9 gene in Arabidopsis thaliana hy5 mutant plants partially complemented the long hypocotyls of hy5 mutant, implying AaLSH9 played a key role as photoresponse factor in cells. In addition, the seed coat color of A. thaliana over-expressing AaLSH9 became lighter than the wide type A.thaliana. Finally, AaCOP1 was confirmed as photoresponse factor to participate in developmental process by stable transgenic A. thaliana.

CONCLUSIONS

AaLSH9 can be involved in kiwifruit (A. arguta) development as key photoresponse factor. Our results not only identified the photoresponse factors AaLSH9 and AaCOP1 but also provided insights into their key role in fruit quality improvement in the process of light response.

Effects of light spectra on morphological characteristics, primary and specialized metabolites of Thymus vulgaris L

Light is a crucial environmental factor that profoundly influences the growth and development of plants. However, the precise mechanisms by which light affects biochemical processes and growth and development factors in Thymus vulgaris remain unknown, necessitating further investigation. Hence, this study aimed to investigate the impact of different light spectra, including red, blue, red-blue, and white lights, on the morphological characteristics, primary, and specialized metabolites of T. vulgaris. Compared to white light, red light significantly increased leaf area (by 64 %), the number of branches (by 132 %), and dry weight (by 6.2 %), although a 40 % reduction in fresh weight was observed under red light conditions. Red-blue light notably enhanced canopy width, fresh weight, and dry weight. Gas chromatography/mass spectrometry (GC/MS) analysis of the plant's essential oil (EO) revealed that p-Cymene and γ-Terpinene were present at the highest levels. Notably, p-Cymene exhibited the highest concentrations under white light and blue light treatments, reaching 60.92 % and 59.53 %, respectively. Moreover, under the same light conditions, phenol and antioxidant levels were significantly elevated. Overall, these findings indicate that red and red-blue light spectra are the most favorable for thyme production.

Functional Characterization of CsF3Ha and Its Promoter in Response to Visible Light and Plant Growth Regulators in the Tea Plant

Flavanone 3-hydroxylase (F3H) catalyzes trihydroxyflavanone formation into dihydroflavonols in the anthocyanin biosynthesis pathway, serving as precursors for anthocyanin synthesis. To investigate the CsF3Ha promoter's regulation in the 'Zijuan' tea plant, we cloned the CsF3Ha gene from this plant. It was up-regulated under various visible light conditions (blue, red, and ultraviolet (UV)) and using plant growth regulators (PGRs), including abscisic acid (ABA), gibberellic acid (GA3), salicylic acid (SA), ethephon, and methyl jasmonate (MeJA). The 1691 bp promoter sequence was cloned. The full-length promoter P1 (1691 bp) and its two deletion derivatives, P2 (890 bp) and P3 (467 bp), were fused with the β-glucuronidase (GUS) reporter gene, and were introduced into tobacco via Agrobacterium-mediated transformation. GUS staining, activity analysis, and relative expression showed that visible light and PGRs responded to promoter fragments. The anthocyanin content analysis revealed a significant increase due to visible light and PGRs. These findings suggest that diverse treatments indirectly enhance anthocyanin accumulation in 'Zijuan' tea plant leaves, establishing a foundation for further research on CsF3Ha promoter activity and its regulatory role in anthocyanin accumulation.

The role of environmental stress in fruit pigmentation

For many fruit crops, the colour of the fruit outwardly defines its eating quality. Fruit pigments provide reproductive advantage for the plant as well as providing protection against unfavourable environmental conditions and pathogens. For consumers these colours are considered attractive and provide many of the dietary benefits derived from fruits. In the majority of species, the main pigments are either carotenoids and/or anthocyanins. They are produced in the fruit as part of the ripening process, orchestrated by phytohormones and an ensuing transcriptional cascade, culminating in pigment biosynthesis. Whilst this is a controlled developmental process, the production of pigments is also attuned to environmental conditions such as light quantity and quality, availability of water and ambient temperature. If these factors intensify to stress levels, fruit tissues respond by increasing (or ceasing) pigment production. In many cases, if the stress is not severe, this can have a positive outcome for fruit quality. Here, we focus on the principal environmental factors (light, temperature and water) that can influence fruit colour.

Impact of Climate Change on Altered Fruit Quality with Organoleptic, Health Benefit, and Nutritional Attributes

As a consequence of global climate change, acute water deficit conditions, soil salinity, and high temperature have been on the rise in their magnitude and frequency, which have been found to impact plant growth and development negatively. However, recent evidence suggests that many fruit plants that face moderate abiotic stresses can result in beneficial effects on the postharvest storage characters of the fruits. Salinity, drought, and high temperature conditions stimulate the synthesis of abscisic acid (ABA), and secondary metabolites, which are vital for fruit quality. The secondary metabolites like phenolic acids and anthocyanins that accumulate under abiotic stress conditions have antioxidant activity, and therefore, such fruits have health benefits too. It has been noticed that fruits accumulate more sugar and anthocyanins owing to upregulation of phenylpropanoid pathway enzymes. The novel information that has been generated thus far indicates that the growth environment during fruit development influences the quality components of the fruits. But the quality depends on the trade-offs between productivity, plant defense, and the frequency, duration, and intensity of stress. In this review, we capture the current knowledge of the irrigation practices for optimizing fruit production in arid and semiarid regions and enhancement in the quality of fruit with the application of exogenous ABA and identify gaps that exist in our understanding of fruit quality under abiotic stress conditions.

Effect of Supplementary Light with Different Wavelengths on Anthocyanin Composition, Sugar Accumulation and Volatile Compound Profiles of Grapes

Protected cultivation is currently one of the main cultivation modes for grape production, but the long-term use of plastic film will have a certain negative impact on the light environment in vineyards, which in turn causes poor colouring, low sugar content and a lack of aroma in some red grape varieties. Supplementing light can be an effective way to mitigate these problems. In this study, vines of three red table grape varieties ('Summer Black', 'Xinyu' and 'Queen Nina') cultivated in a plastic greenhouse were supplemented with red, blue, white and red-blue light from veraison to harvest. All four supplemental light treatments increased the content of anthocyanins, sugars and volatile compounds in three grape varieties compared to CK (no supplemental lighting). Red-blue light treatment was the most favourable for the accumulation of anthocyanins and sugars, and the grapes treated with blue light had the highest content of volatile compounds. The grapes treated with red-blue light all obtained the highest composite scores via principal component analysis. For most of the sensory properties, the highest scores were obtained by the red-blue light-treated grapes. The results of this study will be useful in improving the colouring, sugar, and aroma content of grapes under protected cultivation.

Transcriptome analysis reveals the mechanism for blue-light-induced biosynthesis of delphinidin derivatives in harvested purple pepper fruit

Anthocyanins are the main pigments that affect the color and quality of purple-fruited sweet pepper (Capsicum annuum). Our previous study indicated that blue light can induce anthocyanin accumulation in purple pepper. In view of its underlying mechanism that is unclear, here, anthocyanin content was determined, and transcriptome analysis was performed on pepper fruits harvested from different light treatments. As a result, among the identified anthocyanin metabolites, the levels of delphinidin (Dp) glycosides, including Dp-3-O-rhamnoside, Dp-3-O-rutinoside, and Dp-3-O-glucoside, were highly accumulated in blue-light-treated fruit, which are mainly responsible for the appearance color of purple pepper. Correlation between anthocyanin content and transcriptomic analysis indicated a total of 1,619 upregulated genes were found, of which six structural and 12 transcription factor (TF) genes were involved in the anthocyanin biosynthetic pathway. Structural gene, for instance, CaUFGT as well as TFs such as CaMYC2-like and CaERF113, which were highly expressed under blue light and presented similar expression patterns consistent with Dp glycoside accumulation, may be candidate genes for anthocyanin synthesis in response to blue-light signal.

VvBBX44 and VvMYBA1 form a regulatory feedback loop to balance anthocyanin biosynthesis in grape

Anthocyanins are essential for the quality of perennial horticultural crops, such as grapes. In grapes, ELONGATED HYPOCOTYL 5 (HY5) and MYBA1 are two critical transcription factors that regulate anthocyanin biosynthesis. Our previous work has shown that Vitis vinifera B-box protein 44 (VvBBX44) inhibits anthocyanin synthesis and represses VvHY5 expression in grape calli. However, the regulatory mechanism underlying this regulation was unclear. In this study, we found that loss of VvBBX44 function resulted in increased anthocyanin accumulation in grapevine callus. VvBBX44 directly represses VvMYBA1, which activates VvBBX44. VvMYBA1, but not VvBBX44, directly modulates the expression of grape UDP flavonoid 3-O-glucosyltransferase (VvUFGT). We demonstrated that VvBBX44 represses the transcriptional activation of VvUFGT and VvBBX44 induced by VvMYBA1. However, VvBBX44 and VvMYBA1 did not physically interact in yeast. The application of exogenous anthocyanin stimulated VvBBX44 expression in grapevine suspension cells and tobacco leaves. These findings suggest that VvBBX44 and VvMYBA1 form a transcriptional feedback loop to prevent overaccumulation of anthocyanin and reduce metabolic costs. Our work sheds light on the complex regulatory network that controls anthocyanin biosynthesis in grapevine.

Transcriptomic and Targeted Metabolomics Analysis of Detached Lycium ruthenicum Leaves Reveals Mechanisms of Anthocyanin Biosynthesis Induction through Light Quality and Sucrose Treatments

Light quality and sucrose-induced osmotic stress are known to cause anthocyanin synthesis in detached Lycium ruthenicum leaves. To identify the mechanisms by which the kind of light quality and sucrose concentration are induced, here, we conducted transcriptome sequencing in detached L. ruthenicum leaves treated with different qualities of light and sucrose concentrations. Leaves treated with blue light or sucrose showed a significantly increased total anthocyanins content compared to those treated with white light. Delphinidin-3-O-rutinoside and delphinidin-3-O-glucoside production were differentially regulated by the BL(-S), BL(+S), and WL(+S) treatments. The structural genes CHS, CHI, F3'H, F3'5'H, ANS, and UFGT were significantly up-regulated in leaves treated with blue light or sucrose. Leaves treated with blue light additionally showed up-regulation of the light photoreceptors CRY1, PIF3, COP1, and HY5. The anthocyanin-related genes NCED1, PYR/PYL, PP2C, SnRK2, and ABI5 were significantly up-regulated in leaves treated with sucrose, promoting adaptability to sucrose osmotic stress. Co-expression and cis-regulatory analyses suggested that HY5 and ABI5 could regulate LrMYB44 and LrMYB48 through binding to the G-box element and ABRE element, respectively, inducing anthocyanin synthesis in response to blue light or sucrose treatment. Candidate genes responsive to blue light or sucrose osmotic stress in the anthocyanin biosynthesis pathway were validated through quantitative reverse transcription PCR. These findings deepen our understanding of the mechanisms by which blue light and sucrose-induced osmotic stress regulate anthocyanin synthesis, providing valuable target genes for the future improvement in anthocyanin production in L. ruthenicum.

Genome-Wide Identification of Bilberry WRKY Transcription Factors: Go Wild and Duplicate

WRKY transcription factor genes compose an important family of transcriptional regulators that are present in several plant species. According to previous studies, these genes can also perform important roles in bilberry (Vaccinium myrtillus L.) metabolism, making it essential to deepen our understanding of fruit ripening regulation and anthocyanin biosynthesis. In this context, the detailed characterization of these proteins will provide a comprehensive view of the functional features of VmWRKY genes in different plant organs and in response to different intensities of light. In this study, the investigation of the complete genome of the bilberry identified 76 VmWRKY genes that were evaluated and distributed in all twelve chromosomes. The proteins encoded by these genes were classified into four groups (I, II, III, and IV) based on their conserved domains and zinc finger domain types. Fifteen pairs of VmWRKY genes in segmental duplication and four pairs in tandem duplication were detected. A cis element analysis showed that all promoters of the VmWRKY genes contain at least one potential cis stress-response element. Differential expression analysis of RNA-seq data revealed that VmWRKY genes from bilberry show preferential or specific expression in samples. These findings provide an overview of the functional characterization of these proteins in bilberry.

Light-Induced TaHY5-7A and TaBBX-3B Physically Interact to Promote PURPLE PERICARP-MYB 1 Expression in Purple-Grained Wheat

Purple-grained wheat (Triticum aestivum L.) is an important germplasm source in crop breeding. Anthocyanin biosynthesis in the pericarps of purple-grained wheat is largely light-dependent; however, the regulatory mechanisms underlying light-induced anthocyanin accumulation in the wheat pericarp remain unknown. Here we determined that anthocyanins rapidly accumulate in the pericarps of the purple-grained wheat cultivar Heixiaomai 76 (H76) at 16 days after pollination under light treatment. Using transcriptome sequencing, differential gene expression analysis, and phylogenetic analysis, we identified two key genes involved in light signaling in wheat: ELONGATED HYPOCOTYL 5-7A (TaHY5-7A) and B-BOX-3B (TaBBX-3B). TaHY5-7A and TaBBX-3B were highly expressed in purple-grained wheat pericarps. The heterologous expression of TaHY5-7A partially restored the phenotype of the Arabidopsis (Arabidopsis thaliana) hy5 mutant, resulting in increased anthocyanin accumulation and a shortened hypocotyl. The heterologous expression of TaBBX-3B in wild-type Arabidopsis had similar effects. TaHY5-7A and TaBBX-3B were nucleus-localized, consistent with a function in transcription regulation. However, TaHY5-7A, which lacks a transactivation domain, was not sufficient to activate the expression of PURPLE PERICARP-MYB 1 (TaPpm1), the key anthocyanin biosynthesis regulator in purple pericarps of wheat. TaHY5-7A physically interacted with TaBBX-3B in yeast two-hybrid and bimolecular fluorescence complementation assays. Additionally, TaHY5-7A, together with TaBBX-3B, greatly enhanced the promoter activity of TaPpm1 in a dual luciferase assay. Overall, our results suggest that TaHY5-7A and TaBBX-3B collaboratively activate TaPpm1 expression to promote light-induced anthocyanin biosynthesis in purple-pericarp wheat.

Potential regulatory genes of light induced anthocyanin accumulation in sweet cherry identified by combining transcriptome and metabolome analysis

Anthocyanins exist widely in various plant tissues and organs, and they play an important role in plant reproduction, disease resistance, stress resistance, and protection of human vision. Most fruit anthocyanins can be induced to accumulate by light. Here, we shaded the "Hong Deng" sweet cherry and performed an integrated analysis of its transcriptome and metabolome to explore the role of light in anthocyanin accumulation. The total anthocyanin content of the fruit and two of its anthocyanin components were significantly reduced after the shading. Transcriptome and metabolomics analysis revealed that PAL, 4CL, HCT, ANS and other structural genes of the anthocyanin pathway and cyanidin 3-O-glucoside, cyanidin 3-O-rutinoside, and other metabolites were significantly affected by shading. Weighted total gene network analysis and correlation analysis showed that the upstream and middle structural genes 4CL2, 4CL3, and HCT2 of anthocyanin biosynthesis may be the key genes affecting the anthocyanin content variations in fruits after light shading. Their expression levels may be regulated by transcription factors such as LBD, ERF4, NAC2, NAC3, FKF1, LHY, RVE1, and RVE2. This study revealed for the first time the possible role of LBD, FKF1, and other transcription factors in the light-induced anthocyanin accumulation of sweet cherry, thereby laying a preliminary foundation for further research on the role of light in anthocyanin accumulation of deep red fruit varieties and the genetic breeding of sweet cherry.

Effect of Light of Different Spectral Compositions on Pro/Antioxidant Status, Content of Some Pigments and Secondary Metabolites and Expression of Related Genes in Scots Pine

The aim of this study was to investigate the effect of light quality (white fluorescent light, WFL, containing UV components), red light (RL, 660 nm), blue light (BL, 450 nm), and white LED light (WL, 450 + 580 nm) on the components of the cellular antioxidant system in Pinus sylvestris L. in needles, roots, and hypocotyls, focusing on the accumulation of key secondary metabolites and the expression of related genes. The qualitative and quantitative composition of carotenoids; the content of the main photosynthetic pigments, phenolic compounds, flavonoids (catechins, proanthocyanidins, anthocyanins), ascorbate, and glutathione; the activity of the main antioxidant enzymes; the content of hydrogen peroxide; and the intensity of lipid peroxidation (MDA and 4-HNE contents) were determined. RL resulted in an increase in the content of hydrogen peroxide and 4-HNE, as well as the total fraction of flavonoids in the needles. It also enhanced the expression of several PR (pathogen-related) genes compared to BL and WL. WFL increased the content of phenols, including flavonoids, and enhanced the overall activity of low-molecular antioxidants in needles and hypocotyls. BL increased the content of ascorbate and glutathione, including reduced glutathione, in the needles and simultaneously decreased the activity of peroxidases. Thus, by modifying the light quality, it is possible to regulate the accumulation of secondary metabolites in pine roots and needles, thereby influencing their resistance to various biotic and abiotic stressors.

Persulfidation of transcription factor MYB10 inhibits anthocyanin synthesis in red-skinned pear

Hydrogen sulfide (H2S) is a gaseous signaling molecule that delays color change during fruit ripening. Whether H2S affects anthocyanin biosynthesis in red-skinned pears (Pyrus L.) remains unclear. Here, we found that H2S substantially inhibits anthocyanin accumulation in red-skinned pears and the expression of several genes encoding transcription factors is affected in response to H2S signaling. For example, PyMYB10 and PyMYB73 were down-regulated, whereas PyMYB114 and PyMYB6 were up-regulated. Bioinformatics analysis showed that PyMYB73 and PyMYB6, each containing an EAR motif, may negatively regulate anthocyanin accumulation. Transient expression analysis showed that PyMYB73 substantially promotes anthocyanin biosynthesis by co-transforming with PyMYB10/PyMYB114 + PybHLH3; however, PyMYB6 inhibited anthocyanin biosynthesis in strawberry (Fragaria vesca) receptacles and pear fruits, and PyMYB73 interacted with PyMYB10 and PyMYB6 but not PyMYB114 or PybHLH3. Further investigation showed that Cys194 and Cys218 of PyMYB10 were modified by persulfidation and that PyMYB10Cys218Ala substantially increased anthocyanin accumulation by a transient transformation system. Co-transformation of PyMYB10Cys218Ala + PyMYB73/PyMYB6 also promoted anthocyanin accumulation in pear fruits. Yeast two-hybrid assays showed that the mutation of PyMYB10 did not affect the interaction between PyMYB10 and PyMYB73, but it inhibited interaction with PyMYB6. Moreover, H2S weakened the interaction between PyMYB10 and PyMYB73 but enhanced the interaction with PyMYB6. Thus, we provided a model in which PyMYB10 undergoes persulfidation at Cys218, enhancing the interaction with PyMYB6 and reducing the interaction with PyMYB73. These subsequently results in lower expression of the anthocyanin biosynthesis-related genes Pyrus dihydroflavonol 4-reductase (PyDFR), Pyrus anthocyanidin synthase (PyANS), Pyrus UDP-glucose: flavonoid 3-glucosyl transferase (PyUFGT) and Pyrus glutathione S-transferase (PyGST), thereby inhibiting anthocyanin accumulation in red-skinned pears. Our findings provided a molecular mechanism for H2S-mediated anthocyanin biosynthesis in red-skinned pears.

The blue light signal transduction module FaCRY1-FaCOP1-FaHY5 regulates anthocyanin accumulation in cultivated strawberry

Anthocyanins have important physiological functions and are beneficial to the improvement of fruit quality in strawberry. Light is important for anthocyanin biosynthesis, and specific light quality was identified to promote anthocyanin accumulation in many fruits. However, research on the molecular mechanisms of anthocyanin accumulation regulated by light quality in strawberry remains limited. Here we described the effects of red- and blue-light irradiation on anthocyanin accumulation in strawberry. The results showed that blue light, rather than red light, could lead to the rapid accumulation of anthocyanins after exposure to light for 48 hours. The transcriptional levels of anthocyanin structural and regulatory genes displayed similar trend to the anthocyanin content. To investigate the mechanism of blue light-induced anthocyanin accumulation, the homologs of Arabidopsis blue light signal transduction components, including the blue light photoreceptor FaCRY1, an E3 ubiquitin ligase FaCOP1 and light-responsive factor FaHY5, were cloned from the strawberry cultivar 'Benihoppe'. The protein-protein interaction of FaCRY1-FaCOP1-FaHY5 was revealed by yeast two-hybrid and fluorescence signal assays. Functional complementation analysis showed that overexpression of either FaCOP1 or FaHY5 restored the anthocyanin content and hypocotyl length in corresponding Arabidopsis mutants under blue light. Moreover, dual-luciferase assays showed that FaHY5 could increase the activity of FaRAP (anthocyanin transport gene) promoter and that this function relied on other, likely B-box protein FaBBX22, factors. The overexpression of FaHY5-VP16 (chimeric activator form of FaHY5) and FaBBX22 promoted the accumulation of anthocyanins in transgenic strawberry plants. Further, transcriptomic profiling indicated that the genes involved in the phenylpropanoid biosynthesis pathway were enriched in both FaHY5-VP16-OX and FaBBX22-OX strawberry plants. In summary, our findings provide insights into a mechanism involving the regulation of blue light-induced anthocyanin accumulation via a FaCRY1-FaCOP1-FaHY5 signal transduction module in strawberry.

MutantPpbbx24-delgene positively regulates light-induced anthocyanin accumulation in the red pear.. [DOI: 10.1101/2023.05.19.541476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Anthocyanins are pigments and nutrients in red pears regulated by BBX family genes. Herein, we characterized a 14-nucleotide deletion mutation in the coding region of thePpBBX24gene from ‘Red Zaosu’ pear (Pyrus pyrifoliaWhite Pear Group), namedPpbbx24-del. Genetic and biochemical approaches were used to compare the roles of PpBBX24 and Ppbbx24-del in anthocyanin accumulation.Ppbbx24-delplayed a positive role in anthocyanin biosynthesis of the ‘Red Zaosu’ pear peel by light treatment. Functional analyses based on overexpression in tobacco and transient overexpression in pear fruit peels showed thatPpbbx24-delpromoted anthocyanin accumulation. Cyanidin and peonidin were major differentially expressed anthocyanins, and transcript levels of some structural genes in the anthocyanin biosynthesis pathway were significantly increased. Protein interaction assays showed that PpBBX24 was located in the nucleus and interacted with PpHY5, whereas Ppbbx24-del was colocalized in the nucleoplasm and did not interact with PpHY5. PpHY5 and Ppbbx24-del had positive regulatory effects on the expression ofPpCHS,PpCHI, andPpMYB10when acting alone, but had cumulative effects on gene activation when acting simultaneously. Alone, PpBBX24 had no significant effect on the expression ofPpCHS,PpCHI, orPpMYB10, whereas it inhibited the activation effects of PpHY5 on downstream genes when it existed with PpHY5. Our study demonstrated that mutant Ppbbx24-del positively regulates the anthocyanin accumulation in pear. The results of this study clarify the mechanism and enrich the regulatory network of anthocyanin biosynthesis, which lays a theoretical foundation forPpbbx24-deluse to create red pear cultivars.

Effects of Different Light Wavelengths on Fruit Quality and Gene Expression of Anthocyanin Biosynthesis in Blueberry (Vaccinium corymbosm)

Different light wavelengths display diverse effects on fruit quality formation and anthocyanin biosynthesis. Blueberry is a kind of fruit rich in anthocyanin with important economic and nutritional values. This study explored the effects of different light wavelengths (white (W), red (R), blue (B) and yellow (Y)) on fruit quality and gene expression of anthocyanin biosynthesis in blueberry. We found that the B and W treatments attained the maximum values of fruit width, fruit height and fruit weight in blueberry fruits. The R treatment attained the maximum activities of superoxide dismutase (SOD) and peroxidase (POD), and the Y treatment displayed the maximum contents of ascorbic acid (AsA), glutathione (GSH) and total phenol in fruits, thus improving blueberry-fruit antioxidant capacity. Interestingly, there were differences in the solidity-acid ratio of fruit under different light-wavelength treatments. Moreover, blue light could significantly improve the expression levels of anthocyanin biosynthesis genes and anthocyanin content in fruits. Correlation and principal component analysis showed that total acid content and antioxidant enzymes were significantly negatively correlated with anthocyanin content in blueberry fruits. These results provide new insights for the application of light wavelength to improve blueberry fruit quality and anthocyanin content.

Postharvest light-induced flavonoids accumulation in mango (Mangifera indica L.) peel is associated with the up-regulation of flavonoids-related and light signal pathway genes

INTRODUCTION

Flavonoids are important secondary metabolites in plants and light is a crucial environmental factor regulating flavonoids biosynthesis. However, effect of light on the different flavonoids compositions accumulation in mango and the relevant molecular mechanism still need to be clarified.

METHODS

In this study, green-mature fruits of red mango cultivar 'Zill' were subjected to postharvest light treatment, and fruit peel color, total soluble solids content, total organic acid, and firmness of flesh were measured. The flavonoids metabolites profile, and the expression of flavonoids-related genes and light signal pathway genes were also analyzed.

RESULTS

Results showed that light treatment promoted the red coloration of fruit peel and increased the total soluble solids content and firmness of flesh. The concentration of flavonols, proanthocyanidins and anthocyanins, and expression of key flavonoids biosynthetic genes including MiF3H, MiFLS, MiLAR, MiANS, MiUFGT1, and MiUFGT3 were significantly induced by light. The MYBs regulating flavonols and proanthocyanidins, i.e. MiMYB22 and MiMYB12, as well as the key light signal pathway transcription factors (TFs) MiHY5 and MiHYH, were identified in mango. The transcription of MiMYB1, MiMYB12, MiMYB22, MiHY5 and MiHYH was up-regulated by light.

DISCUSSION

Our results provide a postharvest technology to improve mango fruit appearance quality, and are helpful to reveal the molecular mechanism of light-induced flavonoids biosynthesis in mango.

RNA-Seq reveals the key pathways and genes involved in the light-regulated flavonoids biosynthesis in mango (Mangifera indica L.) peel

Introduction

Flavonoids are important water soluble secondary metabolites in plants, and light is one of the most essential environmental factors regulating flavonoids biosynthesis. In the previous study, we found bagging treatment significantly inhibited the accumulation of flavonols and anthocyanins but promoted the proanthocyanidins accumulation in the fruit peel of mango (Mangifera indica L.) cultivar 'Sensation', while the relevant molecular mechanism is still unknown.

Methods

In this study, RNA-seq was conducted to identify the key pathways and genes involved in the light-regulated flavonoids biosynthesis in mango peel.

Results

By weighted gene co-expression network analysis (WGCNA), 16 flavonoids biosynthetic genes were crucial for different flavonoids compositions biosynthesis under bagging treatment in mango. The higher expression level of LAR (mango026327) in bagged samples might be the reason why light inhibits proanthocyanidins accumulation in mango peel. The reported MYB positively regulating anthocyanins biosynthesis in mango, MiMYB1, has also been identified by WGCNA in this study. Apart from MYB and bHLH, ERF, WRKY and bZIP were the three most important transcription factors (TFs) involved in the light-regulated flavonoids biosynthesis in mango, with both activators and repressors. Surprisingly, two HY5 transcripts, which are usually induced by light, showed higher expression level in bagged samples.

Discussion

Our results provide new insights of the regulatory effect of light on the flavonoids biosynthesis in mango fruit peel.

DNA methylation reprogramming provides insights into light-induced anthocyanin biosynthesis in red pear

DNA methylation, an epigenetic mark, is proposed to regulate plant anthocyanin biosynthesis. It well known that light induces anthocyanin accumulation, with bagging treatments commonly used to investigate light-controlled anthocyanin biosynthesis. We studied the DNA methylome landscape during pear skin coloration under various conditions (fruits re-exposed to sunlight after bag removal). The DNA methylation level in gene body/TE and its flanking sequence was generally similar between debagged and bagged treatments, however differentially methylated regions (DMRs) were re-modelled after light-exposure. Both DNA demethylase homologs and the RNA-directed DNA methylation (RdDM) pathways contributed to this re-distribution. A total of 310 DEGs were DMR-associated during light-induced anthocyanin biosynthesis between debagged and bagged treatments. The hypomethylated mCHH context was seen within the promoter of PyUFGT, together with other anthocyanin biosynthesis genes (PyPAL, PyDFR and PyANS). This enhanced transcriptional activation and promoted anthocyanin accumulation after light re-exposure. Unlike previous reports on bud sports, we did not detect DMRs within the MYB10 promoter. Instead, we observed the genome-wide re-distribution of methylation patterns, suggesting different mechanisms underlying methylation patterns of differentially accumulated anthocyanins caused by either bud mutation or environment change. We investigate the dynamic landscape of genome-scale DNA methylation, which is the combined effect of DNA demethylation and RdDM pathway, in the process of light-induced fruit colour formation in pear. This process is regulated by methylation changes on promoter regions of several DEGs. These results provide a DMR-associated DEGs set and new insight into the mechanism of DNA methylation involved in light-induced anthocyanin biosynthesis.

De-novo transcriptome assembly and analysis of lettuce plants grown under red, blue or white light

Lettuce (Lactuca sativa) is grown in various parts of the world for use as a leafy vegetable. Although the use of light-emitting diode (LED) in controlled plant production systems has been successfully used to enhance nutritional quality and plant growth efficiently, the molecular basis of lettuce's response to varying light spectra is not studied. Using next-generation sequencing, we have analyzed the transcriptomes of leaf lettuce (Lactuca sativa var. 'New Red Fire') grown hydroponically in a modular agricultural production system under three different types of LED lighting: red, blue, and white light. Illumina HiSeq sequencing platform was used to generate paired-end sequence reads (58 Gb raw and 54 Gb clean data) of the transcriptome of lettuce leaves exposed to varying light spectra. The de novo assembled final transcriptome contained 74,096 transcripts. Around 53% and 39% of the assembled transcripts matched to the UniProt and RefSeq RNA sequences, respectively. The validation of the differentially expressed transcripts using RT-qPCR showed complete agreement with RNA-Seq data for 27 transcripts. A comparison of the blue versus red light treatments showed the highest number of significantly differentially expressed transcripts. Among the transcripts significantly up-regulated in blue-light-exposed leaves compared to white-light-exposed leaves, ~ 26% were involved in the 'response to stress'. Among the transcripts significantly upregulated under red light compared to white light, ~ 6% were associated with 'nucleosome assembly' and other processes, such as 'oxidation-reduction process' and 'response to water deprivation' were significantly enriched. Thus, the result from the current study provides deeper insights into differential gene expression patterns and associated functional aspects under varying light qualities.

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.

Early defoliation induces auxin redistribution, promoting paradormancy release in pear buds

Paradormancy of fruit trees occurs in summer and autumn when signals from adjacent organs stimulate buds to develop slowly. This stage has received less attention that the other stages of dormancy, and the underlying mechanism remains uncharacterized. Early defoliation in late summer and early autumn is usually followed by out-of-season blooming in pear (Pyrus spp.), which substantially decreases the number of buds the following spring and negatively affects fruit production. This early bud flush is an example of paradormancy release. Here, we determined that flower bud auxin content is stable after defoliation; however, polar distribution of the pear (Pyrus pyrifolia) PIN-FORMED auxin efflux carrier 1b (PpyPIN1b) implied that auxin tends to be exported from buds. Transcriptome analysis of floral buds after artificial defoliation revealed changes in auxin metabolism, transport, and signal transduction pathways. Exogenous application of a high concentration of the auxin analog 1-naphthaleneacetic acid (300 mg/L) suppressed PpyPIN1b expression and its protein accumulation in the cell membrane, likely leading to decreased auxin efflux from buds, which hindered flower bud sprouting. Furthermore, carbohydrates and additional hormones also influenced out-of-season flowering. Our results indicate that defoliation-induced auxin efflux from buds accelerates bud paradormancy release. This differs from release of apical-dominance-related lateral bud paradormancy after the apex is removed. Our findings and proposed model further elucidate the mechanism underlying paradormancy and will help researchers to develop methods for inhibiting early defoliation-induced out-of-season bud sprouting.

Light-responsive transcription factor PpWRKY44 induces anthocyanin accumulation by regulating PpMYB10 expression in pear

Anthocyanins are a valuable source of antioxidants in the human diet and contribute to fruit coloration. In red-skinned pears, anthocyanin biosynthesis can be induced by light, in which the MYB-bHLH-WDR complex plays a critically important role in transcriptional regulation. However, knowledge of WRKY-mediated transcriptional regulation of light-induced anthocyanin biosynthesis is scarce in red pears. This work identified and functionally characterized a light-inducing WRKY transcription factor, PpWRKY44, in pear. Functional analysis based on overexpressed pear calli showed that PpWRKY44 promoted anthocyanin accumulation. Also, transiently overexpressed PpWRKY44 in pear leaves and fruit peels significantly enhanced the accumulation of anthocyanin, whereas silencing PpWRKY44 in pear fruit peels impaired induction of the accumulation of anthocyanin by light. By chromatin immunoprecipitation and electrophoretic mobility shift assay coupled to a quantitative polymerase chain reaction, we found that PpWRKY44 bound in vivo and in vitro to the PpMYB10 promoter, revealing it as a direct downstream target gene. Moreover, PpWRKY44 was activated by PpBBX18, a light signal transduction pathway component. Our results explained the mechanism mediating the impacts of PpWRKY44 on the transcriptional regulation of anthocyanin accumulation, with potential implications for fine-tuning the fruit peel coloration triggered by light in red pears.

Comparative Metabolome and Transcriptome Analysis of Anthocyanin Biosynthesis in White and Pink Petals of Cotton (Gossypium hirsutum L.)

Upland cotton (Gossypium hirsutum L.) is one of the important fiber crops. Cotton flowers usually appear white (or cream-colored) without colored spots at the petal base, and turn pink on the next day after flowering. In this study, using a mutant showing pink petals with crimson spots at their base, we conducted comparative metabolome and transcriptome analyses to investigate the molecular mechanism of coloration in cotton flowers. Metabolic profiling showed that cyanidin-3-O-glucoside and glycosidic derivatives of pelargonidins and peonidins are the main pigments responsible for the coloration of the pink petals of the mutant. A total of 2443 genes differentially expressed (DEGs) between the white and pink petals were identified by RNA-sequencing. Many DEGs are structural genes and regulatory genes of the anthocyanin biosynthesis pathway. Among them, MYB21, UGT88F3, GSTF12, and VPS32.3 showed significant association with the accumulation of cyanidin-3-O-glucoside in the pink petals. Taken together, our study preliminarily revealed the metabolites responsible for the pink petals and the key genes regulating the biosynthesis and accumulation of anthocyanins in the pink petals. The results provide new insights into the biochemical and molecular mechanism underlying anthocyanin biosynthesis in upland cotton.

B-Box Transcription Factor FaBBX22 Promotes Light-Induced Anthocyanin Accumulation in Strawberry (Fragaria × ananassa)

B-box transcription factors (TFs) play a vital role in light-induced anthocyanin accumulation. Here, the FaBBX22 gene encoding 287 amino acids B-box TF was isolated from the cultivated strawberry variety ‘Benihoppe’ and characterized functionally. The expression analysis showed that FaBBX22 was expressed in the roots, stems, leaves, flowers and fruits, and its transcription level was upregulated under the red- or blue-light irradiation. FaBBX22 was localized in the nucleus and showed trans-acting activity in yeast cells. Ectopic overexpression of FaBBX22 in Arabidopsis enhanced the accumulation of anthocyanin. Additionally, we obtained transgenic strawberry calli that overexpressed the FaBBX22 gene, and strawberry calli coloration assays showed that FaBBX22 increased anthocyanin accumulation by upregulating the expression of anthocyanin biosynthetic genes (FaPAL, FaANS, FaF3′H, FaUFGT1) and transport gene FaRAP in a light-dependent manner. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation assays indicated that FaBBX22 interacted with FaHY5. Furthermore, mutation of the 70th Asp residue in FaBBX22 protein to an Ala residue disrupted the interaction between FaBBX22 and FaHY5. Further, a transient expression assay demonstrated that the co-expression of FaBBX22 and FaHY5 could strongly promote anthocyanin accumulation in strawberry fruits. Collectively, these results revealed the positive regulatory role of FaBBX22 in light-induced anthocyanin accumulation.

Bagging Strategy and Identification of Coloring Mode of ‘Xinqihong’ Pear

‘Xinqihong’ is a recently selected and well-colored red pear (Pyrus bretschneideri Rehd.) cultivar that is popular in the marketplace owing to the bright red color and high quality of the fruit. The red pigmentation is strongly associated with the light signal. However, its responses to bagging treatment and to light exposure after shading are unknown. In this study, the fruit were treated with three types of fruit bags. ’Xinqihong’ fruit colored rapidly in response to light stimulation. A white fruit bag was optimal for bagging of ‘Xinqihong’ fruit. To ensure satisfactory red pigmentation, the fruit required exposure to 30 days of light after bag removal. A transcriptome analysis was conducted to screen light-signal-related genes and identify their possible functions. PbCRY1 activated the promoter of PbHY5.2 and enhanced its expression. PbHY5.2 activated the promoter activity of PbUFGT and induced anthocyanin synthesis, and also showed self-activation characteristics. Both PbCRY2 and PbPHY1 induced anthocyanin accumulation. Thus, blue-light receptors played an important role in anthocyanin synthesis. This study provides a theoretical basis for the bagging cultivation of new varieties of ‘Xinqihong’, and lays a foundation for the study of the mechanisms of red pear fruit coloring in response to light signals.

Two B-Box Proteins, MaBBX20 and MaBBX51, Coordinate Light-Induced Anthocyanin Biosynthesis in Grape Hyacinth

Floral colour is an important agronomic trait that influences the commercial value of ornamental plants. Anthocyanins are a class of flavonoids and confer diverse colours, and elucidating the molecular mechanisms that regulate their pigmentation could facilitate artificial manipulation of flower colour in ornamental plants. Here, we investigated the regulatory mechanism of light-induced anthocyanin biosynthesis during flower colouration in grape hyacinth (Muscari spp.). We studied the function of two B-box proteins, MaBBX20 and MaBBX51. The qPCR revealed that MaBBX20 and MaBBX51 were associated with light-induced anthocyanin biosynthesis. Both MaBBX20 and MaBBX51 are transcript factors and are specifically localised in the nucleus. Besides, overexpression of MaBBX20 in tobacco slightly increased the anthocyanin content of the petals, but reduced in MaBBX51 overexpression lines. The yeast one-hybrid assays indicated that MaBBX20 and MaBBX51 did not directly bind to the MaMybA or MaDFR promoters, but MaHY5 did. The BiFC assay revealed that MaBBX20 and MaBBX51 physically interact with MaHY5. A dual luciferase assay further confirmed that the MaBBX20-MaHY5 complex can strongly activate the MaMybA and MaDFR transcription in tobacco. Moreover, MaBBX51 hampered MaBBX20-MaHY5 complex formation and repressed MaMybA and MaDFR transcription by physically interacting with MaHY5 and MaBBX20. Overall, the results suggest that MaBBX20 positively regulates light-induced anthocyanin biosynthesis in grape hyacinth, whereas MaBBX51 is a negative regulator.

Cryptochrome-mediated blue-light signal contributes to lignin biosynthesis in stone cells in pear fruit

Light environment is an indispensable factor that regulates multitudinous developmental processes during the whole life cycle of plants, including fruit development. Stone cells which negatively influence pear fruit quality because of their strongly lignified cell wall are also affected by light, however, how light qualities influence lignin biosynthesis in pear remains unclear. Here, the calli of European pear (Pyrus communis L.) treated with different lights were used to explore the changes in phenotype, lignin content, and H₂O₂ content, coupled with RNA-Seq and quantitative real-time PCR (qRT-PCR) to investigate the possible regulation pathway of light on lignin biosynthesis in stone cells. Results showed that blue light increased the expression of lignin structure genes and promoted lignin accumulation. Besides, four blue light receptors cryptochromes (CRYs) were identified in white pear, named PbCRY1a (Pbr024556.1), PbCRY1b (Pbr001636.3), PbCRY2a (Pbr023037.1), and PbCRY2b (Pbr002655.4). qRT-PCR analysis showed that PbCRY1a is highly expressed in cultivars with a high content of stone cells. Furthermore, the molecular function of PbCRY1a on stone cell formation in pear fruit was demonstrated by genetic transformation of pear calli and Agrobacterium-mediated transient overexpression in pear fruitlets. Co-expression network analyses with RNA-seq data showed that 8 MYB and 5 NAC genes were classified into different co-expression clusters with lignin biosynthesis genes under blue light conditions. These results indicate that CRY-mediated blue-light signal plays an important role in cell wall lignification and promotes the formation of stone cells in pear by regulating downstream genes.

Transcriptome Analysis Reveals Differences in Anthocyanin Accumulation in Cotton (Gossypium hirsutum L.) Induced by Red and Blue Light

Many factors, including illumination, affect anthocyanin biosynthesis and accumulation in plants. light quality is the key factor affecting the process of photoinduced anthocyanin biosynthesis and accumulation. We observed that the red color of the Upland cotton accession Huiyuan with the R1 mutation turned to normal green color under light-emitting diodes (LEDs), which inspired us to investigate the effect of red and blue lights on the biosynthesis and accumulation of anthocyanins. We found that both red and blue lights elevated accumulation of anthocyanins. Comparative transcriptomic analyses, including Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) and GSEA, revealed that genes differentially expressed under different light conditions were enriched with the pathways of circadian rhythm, phenylpropanoid biosynthesis, anthocyanin biosynthesis, and flavone and flavonol biosynthesis. Not surprisingly, all the major structural genes related to biosynthesis of anthocyanins, including the key regulatory MYB transcription factor (GhPAP1D) and anthocyanin transporter (GhGSTF12), were induced by red or blue light treatment. However, LARs and MATEs related to biosynthesis of proanthocyanidins were more significantly up-regulated by red light radiation than by blue light radiation. Vice versa, the accumulation of anthocyanins under red light was not as high as that under blue light. In addition, we demonstrated a potential role of GhHY5, a key regulator in plant circadian rhythms, in regulation of anthocyanin accumulation, which could be achieved via interaction with GhPAP1D. Together, these results indicate different effect of red and blue lights on biosynthesis and accumulation of anthocyanins and a potential module including GhHY5 and GhPAP1D in regulation of anthocyanin accumulation in cotton. These results also suggest that the substrates responsible the synthesis of anthocyanins under blue light is diverted to biosynthesis of proanthocyanidin under red light.

Influence of Climate Change on Metabolism and Biological Characteristics in Perennial Woody Fruit Crops in the Mediterranean Environment

The changes in the state of the climate have a high impact on perennial fruit crops thus threatening food availability. Indeed, climatic factors affect several plant aspects, such as phenological stages, physiological processes, disease-pest frequency, yield, and qualitative composition of the plant tissues and derived products. To mitigate the effects of climatic parameters variability, plants implement several strategies of defense, by changing phenological trends, altering physiology, increasing carbon sequestration, and metabolites synthesis. This review was divided into two sections. The first provides data on climate change in the last years and a general consideration on their impact, mitigation, and resilience in the production of food crops. The second section reviews the consequences of climate change on the industry of two woody fruit crops models (evergreen and deciduous trees). The research focused on, citrus, olive, and loquat as evergreen trees examples; while grape, apple, pear, cherry, apricot, almond, peach, kiwi, fig, and persimmon as deciduous species. Perennial fruit crops originated by a complex of decisions valuable in a long period and involving economic and technical problems that farmers may quickly change in the case of annual crops. However, the low flexibility of woody crops is balanced by resilience in the long-life cycle.

Transcriptional regulation of KCS gene by bZIP29 and MYB70 transcription factors during ABA-stimulated wound suberization of kiwifruit (Actinidia deliciosa)

BACKGROUND

Our previous study has demonstrated that the transcription of AchnKCS involved in suberin biosynthesis was up-regulated by exogenous abscisic acid (ABA) during the wound suberization of kiwifruit, but the regulatory mechanism has not been fully elucidated.

RESULTS

Through subcellular localization analysis in this work, AchnbZIP29 and AchnMYB70 transcription factors were observed to be localized in the nucleus. Yeast one-hybrid and dual-luciferase assay proved the transcriptional activation of AchnMYB70 and transcriptional suppression of AchnbZIP29 on AchnKCS promoter. Furthermore, the transcription level of AchnMYB70 was enhanced by ABA during wound suberization of kiwifruit, but AchnbZIP29 transcription was reduced by ABA.

CONCLUSIONS

Therefore, it was believed that ABA enhanced the transcriptional activation of AchnMYB70 on AchnKCS by increasing AchnMYB70 expression. On the contrary, ABA relieved the inhibitory effect of AchnbZIP29 on transcription of AchnKCS by inhibiting AchnbZIP29 expression. These results gave further insight into the molecular regulatory network of ABA in wound suberization of kiwifruit.

Pear genetics: Recent advances, new prospects, and a roadmap for the future

Pear, belonging to the genus Pyrus, is one of the most economically important temperate fruit crops. Pyrus is an important genus of the Rosaceae family, subfamily Maloideae, and has at least 22 different species with over 5000 accessions maintained or identified worldwide. With the release of draft whole-genome sequences for Pyrus, opportunities for pursuing studies on the evolution, domestication, and molecular breeding of pear, as well as for conducting comparative genomics analyses within the Rosaceae family, have been greatly expanded. In this review, we highlight key advances in pear genetics, genomics, and breeding driven by the availability of whole-genome sequences, including whole-genome resequencing efforts, pear domestication, and evolution. We cover updates on new resources for undertaking gene identification and molecular breeding, as well as for pursuing functional validation of genes associated with desirable economic traits. We also explore future directions for "pear-omics".

Anthocyanin-mediated arsenic tolerance in plants

Plants detoxify toxic metal(loid)s by accumulating diverse metabolites. Beside scavenging excess reactive oxygen species (ROS) induced by metal(loid)s, some metabolites chelate metal(loid) ions. Classically, thiol-containing compounds, especially glutathione (GSH) and phytochelatins (PCs) are thought to be the major chelators that conjugate with metal(loid)s in the cytoplasm followed by transport and sequestration in the vacuole. In addition to this classical detoxification pathway, a role for secondary metabolites in metal(loid) detoxification has recently emerged. In particular, anthocyanins, a kind of flavonoids with ROS scavenging potential, contribute to enhanced arsenic tolerance in several plant species. Evidence is accumulating that, in analogy to GSH and PCs, anthocyanins may conjugate with arsenic followed by vacuolar sequestration in the detoxification event. Exogenous application or endogenous accumulation of anthocyanins enhances arsenic tolerance, leading to improved plant growth and productivity. The application of some plant hormones and signaling molecules stimulates endogenous anthocyanin synthesis which confers tolerance to arsenic stress. Anthocyanin biosynthesis is transcriptionally regulated by several transcription factors, including myeloblastosis (MYBs). The light-regulated transcription factor elongated hypocotyl 5 (HY5) also affects anthocyanin biosynthesis, but its role in arsenic tolerance remains elusive. Here, we review the mechanism of arsenic detoxification in plants and the potential role of anthocyanins in arsenic tolerance beyond the classical points of view. Our analysis proposes that anthocyanin manipulation in crop plants may ensure sustainable crop yield and food safety in the marginal lands prone to arsenic pollution.

Genome-wide identification of Pistacia R2R3-MYB gene family and function characterization of PcMYB113 during autumn leaf coloration in Pistacia chinensis

Pistacia chinensis is known for its biodiesel production. Several varieties of this plant have leaves that produce anthocyanin, which is responsible for their reddish coloration in autumn. This reddish hue is what makes them useful as ornamental plants. However, the mechanism of anthocyanin accumulation during autumn leaf coloration remains unclear. R2R3-MYB proteins reportedly regulated anthocyanin biosynthesis in many plant species. Here, we performed a genome-wide analysis and expression profiles of R2R3-MYB transcription factor in Pistacia. A total of 158 R2R3-MYB proteins were identified and grouped into 32 clades. Combining the data from RNA-seq and qRT-PCR, one key gene, EVM0016534, was screened and identified to have the highest correlation with anthocyanin accumulation. It was named PcMYB113 due to its sequence similarity to AtMYB113 and it could bind to the promoter of PcF3H. Furthermore, ectopic expression of PcMYB113 in Arabidopsis promoted the accumulation of anthocyanin in the seed coat, cotyledon, and mature leaves, thus confirming the function of PcMYB113 in anthocyanin biosynthesis. In addition, PcMYB113 had a specifically higher expression in senesced red leaves than in mature green leaves and young red leaves in P. chinensis, thereby suggesting the potential role of PcMYB113 in promoting anthocyanin biosynthesis during autumn leaf coloration. These findings enrich our understanding of the function of R2R3-MYB genes in anthocyanin biosynthesis and autumn leaf coloration.

Emerging roles of brassinosteroids and light in anthocyanin biosynthesis and ripeness of climacteric and non-climacteric fruits

Anthocyanins are important pigments that contribute to fruit quality. The regulation of anthocyanin biosynthesis by several transcription factors via sophisticated regulatory networks has been studied in various plants. Brassinosteroids (BRs), a new class of plant hormone, are involved in regulating anthocyanin biosynthesis in fruits. Furthermore, light directly affects the synthesis and distribution of anthocyanins. Here, we summarize the recent progress toward understanding the impact of BR and light on anthocyanin biosynthesis in climacteric and non-climacteric fruits. We review the BR and light signaling pathways and highlight the important transcription factors that are associated with the synthesis of anthocyanins, such as BZR1 (brassinazole-resistant 1, BR signaling pathway), HY5 (elongated hypocotyl 5) and COP1 (constitutively photomorphogenic 1, light signal transduction pathway), which bind with the target genes involved in anthocyanin synthesis. In addition, we review the mechanism by which light signals interact with hormonal signals to regulate anthocyanin biosynthesis.

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.