Ultraviolet A-specific induction of anthocyanin biosynthesis in the swollen hypocotyls of turnip (Brassica rapa)

Lily (Lilium spp.) LhERF4 negatively affects anthocyanin biosynthesis by suppressing LhMYBSPLATTER transcription

Anthocyanins are among the main pigments involved in the colouration of Asiatic hybrid lily (Lilium spp.). Ethylene, a plant ripening hormone, plays an important role in promoting plant maturation and anthocyanin biosynthesis. However, whether and how ethylene regulates anthocyanin biosynthesis in lily tepals have not been characterized. Using yeast one-hybrid screening, we previously identified an APETALA2 (AP2)/ETHYLENE RESPONSE FACTOR (ERF) named LhERF4 as a potential inhibitor of LhMYBSPLATTER-mediated negative regulation of anthocyanin biosynthesis in lily. Here, transcript and protein analysis of LhERF4, a transcriptional repressor, revealed that LhERF4 directly binds to the promoter of LhMYBSPLATTER. In addition, overexpression of LhERF4 in lily tepals negatively regulates the expression of key structural genes and the total anthocyanin content by suppressing the LhMYBSPLATTER gene. Moreover, the LhERF4 gene inhibits anthocyanin biosynthesis in response to ethylene, affecting anthocyanin accumulation and pigmentation in lily tepals. Collectively, our findings will advance and elucidate a novel regulatory network of anthocyanin biosynthesis in lily, and this research provides new insight into colouration regulation.

Characterization and Functional Analysis of Chalcone Synthase Genes in Highbush Blueberry (Vaccinium corymbosum)

Chalcone synthase (CHS) is the first key enzyme-catalyzing plant flavonoid biosynthesis. Until now, however, the blueberry CHS gene family has not been systematically characterized and studied. In this study, we identified 22 CHS genes that could be further classified into four subfamilies from the highbush blueberry (Vaccinium corymbosum) genome. This classification was well supported by the high nucleotide and protein sequence similarities and similar gene structure and conserved motifs among VcCHS members from the same subfamily. Gene duplication analysis revealed that the expansion of the blueberry CHS gene family was mainly caused by segmental duplications. Promoter analysis revealed that the promoter regions of VcCHSs contained numerous cis-acting elements responsive to light, phytohormone and stress, along with binding sites for 36 different types of transcription factors. Gene expression analysis revealed that Subfamily I VcCHSs highly expressed in fruits at late ripening stages. Through transient overexpression, we found that three VcCHSs (VcCHS13 from subfamily II; VcCHS8 and VcCHS21 from subfamily I) could significantly enhance the anthocyanin accumulation and up-regulate the expression of flavonoid biosynthetic structural genes in blueberry leaves and apple fruits. Notably, the promoting effect of the Subfamily I member VcCHS21 was the best. The promoter of VcCHS21 contains a G-box (CACGTG) and an E-box sequence, as well as a bHLH binding site. A yeast one hybridization (Y1H) assay revealed that three anthocyanin biosynthesis regulatory bHLHs (VcAN1, VcbHLH1-1 and VcbHLH1-2) could specifically bind to the G-box sequence (CACGTG) in the VcCHS21 promoter, indicating that the expression of VcCHS21 was regulated by bHLHs. Our study will be helpful for understanding the characteristics and functions of blueberry CHSs.

Phenotypic, Physiological, and Molecular Response of Loropetalum chinense var. rubrum under Different Light Quality Treatments Based on Leaf Color Changes

Light quality is a vital environmental signal used to trigger growth and to develop structural differentiation in plants, and it influences morphological, physiological, and biochemical metabolites. In previous studies, different light qualities were found to regulate the synthesis of anthocyanin. However, the mechanism of the synthesis and accumulation of anthocyanins in leaves in response to light quality remains unclear. In this study, the Loropetalum chinense var. rubrum "Xiangnong Fendai" plant was treated with white light (WL), blue light (BL), ultraviolet-A light (UL), and blue light plus ultraviolet-A light (BL + UL), respectively. Under BL, the leaves were described as increasing in redness from "olive green" to "reddish-brown". The chlorophyll, carotenoid, anthocyanin, and total flavonoid content were significantly higher at 7 d than at 0 d. In addition, BL treatment also significantly increased the accumulation of soluble sugar and soluble protein. In contrast to BL, ultraviolet-A light increased the malondialdehyde (MDA) content and the activities of three antioxidant enzymes in the leaves, including catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD), in varying degrees over time. Moreover, we also found that the CRY-like gene, HY5-like gene, BBX-like gene, MYB-like gene, CHS-like gene, DFR-like gene, ANS-like gene, and UFGT-like gene were significantly upregulated. Furthermore, the SOD-like, POD-like, and CAT-like gene expressions related to antioxidase synthesis were found under ultraviolet-A light conditions. In summary, BL is more conducive to reddening the leaves of "Xiangnong Fendai" and will not lead to excessive photooxidation. This provides an effective ecological strategy for light-induced leaf-color changes, thereby promoting the ornamental and economic value of L. chinense var. rubrum.

Genome-Wide Identification and Characterization of WRKY Transcription Factors and Their Expression Profile in Loropetalum chinense var. rubrum

The WRKY gene family plays important roles in plant growth and development, as well as in the responses to biotic and abiotic stresses. Loropetalum chinense var. rubrum has high ornamental and medicinal value. However, few WRKY genes have been reported in this plant, and their functions remain unknown. To explore the roles that the WRKY genes play in L. chinense var. rubrum, we identified and characterized 79 LcWRKYs through BLAST homology analysis and renamed them (as LcWRKY1-79) based on their distribution on the chromosomes of L. chinense var. rubrum. In this way, according to their structural characteristics and phylogenetic analysis, they were divided into three groups containing 16 (Group I), 52 (Group II), and 11 (Group III) WRKYs, respectively. LcWRKYs in the same group have similar motifs and gene structures; for instance, Motifs 1, 2, 3, 4, and 10 constitute the WRKY domain and zinc-finger structure. The LcWRKY promoter region contains light response elements (ACE, G-box), stress response elements (TC-rich repeats), hormone response elements (TATC-box, TCA-element), and MYB binding sites (MBS, MBSI). Synteny analysis of LcWRKYs allowed us to establish orthologous relationships among the WRKY gene families of Arabidopsis thaliana, Oryza sativa, Solanum lycopersicum L., Vitis vinifera L., Oryza sativa L., and Zea mays L.; furthermore, analysis of the transcriptomes of mature leaves and flowers from different cultivars demonstrated the cultivar-specific LcWRKY gene expression. The expression levels of certain LcWRKY genes also presented responsive changes from young to mature leaves, based on an analysis of the transcriptome in leaves at different developmental stages. White light treatment led to a significant decrease in the expression of LcWRKY6, 18, 24, 34, 36, 44, 48, 61, 62, and 77 and a significant increase in the expression of LcWRKY41, blue light treatment led to a significant decrease in the expression of LcWRKY18, 34, 50, and 77 and a significant increase in the expression of LcWRKY36 and 48. These results enable a better understanding of LcWRKYs, facilitating the further exploration of their genetic functions and the molecular breeding of L. chinense var. rubrum.

Multilevel regulation of anthocyanin-promoting R2R3-MYB transcription factors in plants

Anthocyanins are common secondary metabolites in plants that confer red, blue, and purple colorations in plants and are highly desired by consumers for their visual appearance and nutritional quality. In the last two decades, the anthocyanin biosynthetic pathway and transcriptional regulation of anthocyanin biosynthetic genes (ABGs) have been well characterized in many plants. From numerous studies on model plants and horticultural crops, many signaling regulators have been found to control anthocyanin accumulation via regulation of anthocyanin-promoting R2R3-MYB transcription factors (so-called R2R3-MYB activators). The regulatory mechanism of R2R3-MYB activators is mediated by multiple environmental factors (e.g., light, temperature) and internal signals (e.g., sugar, ethylene, and JA) in complicated interactions at multiple levels. Here, we summarize the transcriptional control of R2R3-MYB activators as a result of natural variations in the promoter of their encoding genes, upstream transcription factors and epigenetics, and posttranslational modifications of R2R3-MYB that determine color variations of horticultural plants. In addition, we focus on progress in elucidating the integrated regulatory network of anthocyanin biosynthesis mediated by R2R3-MYB activators in response to multiple signals. We also highlight a few gene cascade modules involved in the regulation of anthocyanin-related R2R3-MYB to provide insights into anthocyanin production in horticultural plants.

A single amino acid substitution in the R2R3 conserved domain of the BrPAP1a transcription factor impairs anthocyanin production in turnip (Brassica rapa subsp. rapa)

The purple pigmentation in the epidermis of swollen roots of 'Tsuda' turnip (Brassica rapa subsp. rapa) is induced by light, providing a good system to investigate the genetic mechanism of light-dependent anthocyanin biosynthesis in B. rapa. Here, we identified the R2R3 MYB transcription factor gene PRODUCTION OF ANTHOCYANIN PIGMENT1 (BrPAP1a) as the critical gene in the anthocyanin-defective mutant w68. A nucleotide mutation in the turn region of the R3 domain was screened, which caused an amino acid substitution from glycine to serine (G94S). Functional analysis showed that the interaction of BrPAP1a with two bHLH factors ENHANCER OF GLABRA 3 (BrEGL3) and TRANSPARENT TESTA 8 (BrTT8) were impaired by the mutation. Expression of BrTT8 was activated by BrPAP1a and enhanced by MYB-bHLH-WDR (MBW) complexes, but blocked by the mutation. Furthermore, BrPAP1a directly bound the MYB-recognizing element (MRE) in the BrTT8 promoter, while the G94S substitution caused a loss of DNA-binding activity. Our findings indicate that G94 is required for protein interaction with BrTT8 and BrEGL3 and DNA-binding of BrPAP1a to activate BrTT8 expression, which leads to anthocyanin biosynthesis. Collectively, our data indicate the importance of the highly conserved amino acids within R2R3 MYB proteins in regulating anthocyanin biosynthesis and could aid programs to increase anthocyanins in turnip roots.

BrLETM2 Protein Modulates Anthocyanin Accumulation by Promoting ROS Production in Turnip (Brassica rapa subsp. rapa)

In ‘Tsuda’ turnip, the swollen root peel accumulates anthocyanin pigments in a light-dependent manner, but the mechanism is unclear. Here, mutant g120w which accumulated extremely low levels of anthocyanin after light exposure was identified. Segregation analysis showed that the anthocyanin-deficient phenotype was controlled by a single recessive gene. By using bulked-segregant analysis sequencing and CAPS marker-based genetic mapping analyses, a 21.6-kb region on chromosome A07 was mapped, in which a calcium-binding EF hand family protein named BrLETM2 was identified as the causal gene. RNA sequencing analysis showed that differentially expressed genes (DEGs) between wild type and g120w in light-exposed swollen root peels were enriched in anthocyanin biosynthetic process and reactive oxygen species (ROS) biosynthetic process GO term. Furthermore, nitroblue tetrazolium (NBT) staining showed that the ROS level decreased in g120w mutant. Anthocyanins induced by UV-A were abolished by the pre-treatment of seedlings with DPI (an inhibitor of nicotinamide adenine nucleoside phosphorylase (NADPH) oxidase) and decreased in g120w mutant. These results indicate that BrLETM2 modulates ROS signaling to promote anthocyanin accumulation in turnip under UV-A and provides new insight into the mechanism of how ROS and light regulate anthocyanin production.

Molecular cloning and characterization of chalcone synthase gene from Coelogyne ovalis Lindl. and its stress-dependent expression

Chalcone synthase (CHS, EC 2.3.1.74) is one of the key and rate-limiting enzymes of phenylpropanoid pathway which plays superior roles in the production of secondary metabolites. In the present study a full-length cDNA of CHS gene was isolated and characterized from Coelogyne ovalis, an orchid of ornamental and medicinal importance. The CHS gene sequence from C. ovalis (CoCHS) was found to be 1445 bp and comprised an open reading frame of 1182 bp, encoding for 394 amino acid residues. Further, the sequence alignment and phylogenetic analysis revealed that CoCHS protein shared high degree of similarity with CHS protein of other orchid species. It also confirmed that it contained all four motifs (I to IV) and signature sequence for the functionality of this gene. Structural modeling of CoCHS based on the crystallographic structure of Freesia hybrida indicated that CoCHS had a similar structure. Quantitative polymerase chain reaction (qPCR) disclosed that CoCHS was expressed in all tissues examined, with the highest transcript being in leaves, followed by pseudobulbs and roots. CoCHS expression was also evaluated in the in vitro-raised plantlets under the abiotic stress (dark, cold, UV-B, wounding, salinity). mRNA transcript expression of CHS gene was found to be positively enhanced and regulated by the different stress types. A correlation between the CoCHS transcript expression with flavonoid and anthocyanin contents revealed that a positive correlation existed between metabolites' content and CoCHS expression within the in vivo as well as in the in vitro-raised plant parts.

UV radiation increases phenolic compound protection but decreases reproduction in Silene littorea

Plants respond to changes in ultraviolet (UV) radiation both morphologically and physiologically. Among the variety of plant UV-responses, the synthesis of UV-absorbing flavonoids constitutes an effective non-enzymatic mechanism to mitigate photoinhibitory and photooxidative damage caused by UV stress, either reducing the penetration of incident UV radiation or acting as quenchers of reactive oxygen species (ROS). In this study, we designed a UV-exclusion experiment to investigate the effects of UV radiation in Silene littorea. We spectrophotometrically quantified concentrations of both anthocyanins and UV-absorbing phenolic compounds in petals, calyces, leaves and stems. Furthermore, we analyzed the UV effect on the photosynthetic activity in hours of maximum solar radiation and we tested the impact of UV radiation on male and female reproductive performance. We found that anthocyanin concentrations showed a significant decrease of about 20% with UV-exclusion in petals and stems, and a 30% decrease in calyces. The concentrations of UV-absorbing compounds under UV-exclusion decreased by approximately 25% in calyces and stems, and 12% in leaves. Photochemical efficiency of plants grown under UV decreased at maximum light stress, reaching an inhibition of 58% of photosynthetic activity, but their ability to recover after light-stress was not affected. In addition, exposure to UV radiation did not affect ovule production or seed set per flower, but decreased pollen production and total seed production per plant by 31% and 69%, respectively. Our results demonstrate that UV exposure produced opposing effects on the accumulation of plant phenolic compounds and reproduction. UV radiation increased the concentration of phenolic compounds, suggesting a photoprotective role of plant phenolics against UV light, yet overall reproduction was compromised.

BrmiR828 Targets BrPAP1, BrMYB82, and BrTAS4 Involved in the Light Induced Anthocyanin Biosynthetic Pathway in Brassica rapa

Comprehensive research in various plants shows that the metabolic pathway of anthocyanin biosynthesis is affected by environmental factors and regulated by microRNAs through post-transcriptional regulation. In seedlings of Brassica rapa Tsuda, the accumulation of anthocyanin is induced by light. However, the roles of BrmiR828 in the light-induced synthesis of anthocyanin in Brassica rapa remain to be explored. Here, a primary transcript of BrmiR828 was identified to be located on the chromosomes of the A03 sub-genome. Five candidate MYB family genes were predicted as targets of BrmiR828 in the database of Brassica rapa (BRAD, V1.1) by using psRNATarget. The transcript abundance of mature BrmiR828 was reduced in seedlings of Brassica rapa Tsuda under blue light irradiation comparing with dark treatment. However, Real-time PCR showed the transcript level of the five candidate targets, Bra004162, Bra022602, Bra001917, Bra029113, and Bra039763 was up-regulated when the seedlings exposed to blue or UV-A light. Trans-acting siRNA gene 4 (BrTAS4) was also identified to have a higher transcript level under blue and UV-A light irradiation than that in dark treatment. RNA ligase mediated 5′amplification of cDNA ends (RLM-5′ RACE) showed that BrmiR828 can splice the mRNA of Bra039763, Bra022602, and BrTAS4 on binding sites. Phylogenetic analysis of candidate BrMYBs targets along with MYBs from Arabidopsis thaliana showed that Bra039763, Bra004162, Bra001917, Bra029113, and Bra022602 are classified to the same group with AtMYB75, AtMYB114, AtMYB90, AtMYB113, and AtMYB82 which are involved in the anthocyanin biosynthetic pathway. As a result, light-induced down-regulation of BrmiR828 can target BrTAS4, BrPAP1 (Bra039763), MYB82 (Bra022602) to negatively regulate their transcript levels leading to the accumulation of MYB transcription factors that positively regulate anthocyanin biosynthesis in light-exposed seedlings of Brassica rapa.

Transcriptomic profiling of purple broccoli reveals light-induced anthocyanin biosynthetic signaling and structural genes

Purple Broccoli (Brassica oleracea L. var italica) attracts growing attention as a functional food. Its purple coloration is due to high anthocyanin amounts. Light represents a critical parameter affecting anthocyanins biosynthesis. In this study, 'Purple Broccoli', a light-responding pigmentation cultivar, was assessed for exploring the mechanism underlying light-induced anthocyanin biosynthesis by RNA-Seq. Cyanidin, delphinidin and malvidin derivatives were detected in broccoli head samples. Shading assays and RNA-seq analysis identified the flower head as more critical organ compared with leaves. Anthocyanin levels were assessed at 0, 7 and 11 days, respectively, with further valuation by RNA-seq under head-shading and light conditions. RNA sequences were de novo assembled into 50,329 unigenes, of which 38,701 were annotated against four public protein databases. Cluster analysis demonstrated that anthocyanin/phenylpropanoid biosynthesis, photosynthesis, and flavonoid biosynthesis in cluster 8 were the main metabolic pathways regulated by light and had showed associations with flower head growth. A total of 2,400 unigenes showed differential expression between the light and head-shading groups in cluster 8, including 650 co-expressed, 373 specifically expressed under shading conditions and 1,377 specifically expressed under normal light. Digital gene expression (DGE) analysis demonstrated that light perception and the signal transducers CRY3 and HY5 may control anthocyanin accumulation. Following shading, 15 structural genes involved in anthocyanin biosynthesis were downregulated, including PAL, C4H, 4CL, CHS, CHI, F3H and DFR. Moreover, six BoMYB genes (BoMYB6-1, BoMYB6-2, BoMYB6-3, BoMYB6-4, BoMYBL2-1 and BoMYBL2-2) and three BobHLH genes (BoTT8_5-1, BoTT8_5-2 and BoEGL5-3) were critical transcription factors controlling anthocyanin accumulation under light conditions. Based on these data, a light-associated anthocyanin biosynthesis pathway in Broccoli was proposed. This information could help improve broccoli properties, providing novel insights into the molecular mechanisms underpinning light-associated anthocyanin production in purple vegetables.

The Effects of Ultraviolet A/B Treatments on Anthocyanin Accumulation and Gene Expression in Dark-Purple Tea Cultivar 'Ziyan' (Camellia sinensis)

‘Ziyan’ is a novel anthocyanin-rich tea cultivar with dark purple young shoots. However, how its anthocyanin accumulation is affected by environmental factors, such as ultraviolet (UV), remains unclear. In this study, we observed that UV light treatments stimulated anthocyanin accumulation in ‘Ziyan’ leaves, and we further analyzed the underlying mechanisms at gene expression and enzyme activity levels. In addition, the catechins and chlorophyll contents of young shoots under different light treatments were also changed. The results showed that the contents of total anthocyanins and three major anthocyanin molecules, i.e., delphinidin, cyanidin, and pelargonidin, were significantly higher in leaves under UV-A, UV-B, and UV-AB treatments than those under white light treatment alone. However, the total catechins and chlorophyll contents in these purple tea plant leaves displayed the opposite trends. The anthocyanin content was the highest under UV-A treatment, which was higher by about 66% than control. Compared with the white light treatment alone, the enzyme activities of chalcone synthase (CHS), flavonoid 3′,5′-hydroxylase (F3′5′H), and anthocyanidin synthase (ANS) under UV treatments increased significantly, whereas the leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR) activities reduced. There was no significant difference in dihydroflavonol 4-reductase (DFR) activity under all treatments. Comparative transcriptome analyses unveiled that there were 565 differentially expressed genes (DEGs) of 29,648 genes in three pair-wise comparisons (white light versus UV-A, W vs. UV-A; white light versus UV-B, W vs. UV-A; white light versus UV-AB, W vs. UV-AB). The structural genes in anthocyanin pathway such as flavanone 3-hydroxylase (F3H), F3′5′H, DFR, and ANS, and regulatory gene TT8 were upregulated under UV-A treatment; F3′5′H, DFR, ANS, and UFGT and regulatory genes EGL1 and TT2 were upregulated under UV-AB treatment. However, most structural genes involved in phenylpropanoid and flavonoid pathways were downregulated under UV-B treatment compared with control. The expression of LAR and ANR were repressed in all UV treatments. Our results indicated that UV-A and UV-B radiations can induce anthocyanin accumulation in tea plant ‘Ziyan’ by upregulating the structural and regulatory genes involved in anthocyanin biosynthesis. In addition, UV radiation repressed the expression levels of LAR, ANR, and FLS, resulting in reduced ANR activity and a metabolic flux shift toward anthocyanin biosynthesis.

Photoresponse to different lighting strategies during red leaf lettuce growth

The objective of the study was to investigate the effects of growth-stage specific lighting for the physiological homeostasis of red leaf lettuce (Lactuca sativa L. cv. Red Cos), by measuring the productivity of photosynthesis and primary metabolism. In the experiments, the main photosynthetic photon flux consisted of red (R) and blue (B) light, supplemented with blue, green (G) or UV-A wavelengths. Decrease of fructose, accompanied by significant decrease of stomatal conductance (gs), the ratio of intracellular to ambient CO2 concentration (Ci/Ca), photosynthetic rate (Pr), light adapted actual quantum yield of PSII photochemistry (ΦPSII), biomass formation and significant increase of transpiration rate (Tr) suggest that supplemental UV-A during maturity stage, after supplemental green irradiation during seedling stage (BRG to BRUV) was the least favourable condition for red leaf lettuce. However, constant irradiation with supplemental green (BRG) or supplemental green irradiation after increased blue exposure (B↑R to BRG) resulted in significant increase of Pr, gs, Ci/Ca, and light use efficiency(LUE), and decrease of Tr and Water use efficiency (WUE). Significant increase of leaf area was observed under supplemental green in both seedlings (BR; BRG) and matured plants (B↑R to BRG). Significant increase of specific leaf area was found under supplemental green (BRG) for seedlings and under increased blue (B↑R) for matured plants. Accordingly, the most favourable growth-stage specific lighting spectrum strategy for red leaf lettuce, based on photosynthetic and primary metabolite response, is supplemental green irradiation after increased blue exposure (B↑R to BRG), whereas, the most favourable condition for seedlings is BRG. According to the PCA correlation matrix, associations among the measured data indicate that WUE negatively correlated with gs and Ci/Ca, while LUE positively correlated with gs and Pr. However, weak correlations between ФPSII, LUE and photochemical reflectance index (PRI) suggest that selected light conditions were not optimal for red leaf lettuce.

Chalcone synthases (CHSs): the symbolic type III polyketide synthases

Present review provides a thorough insight on some significant aspects of CHSs over a period of about past three decades with a better outlook for future studies toward comprehending the structural and mechanistic intricacy of this symbolic enzyme. Polyketide synthases (PKSs) form a large family of iteratively acting multifunctional proteins that are involved in the biosynthesis of spectrum of natural products. They exhibit remarkable versatility in the structural configuration and functional organization with an incredible ability to generate different classes of compounds other than the characteristic secondary metabolite constituents. Architecturally, chalcone synthase (CHS) is considered to be the simplest representative of Type III PKSs. The enzyme is pivotal for phenylpropanoid biosynthesis and is also well known for catalyzing the initial step of the flavonoid/isoflavonoid pathway. Being the first Type III enzyme to be discovered, CHS has been subjected to ample investigations which, to a greater extent, have tried to understand its structural complexity and promiscuous functional behavior. In this context, we vehemently tried to collect the fragmented information entirely focussed on this symbolic enzyme from about past three-four decades. The aim of this review is to selectively summarize data on some of the fundamental aspects of CHSs viz, its history and distribution, localization, structure and analogs in non-plant hosts, promoter analyses, and role in defense, with an emphasis on mechanistic studies in different species and vis-à-vis mutation-led changes, and evolutionary significance which has been discussed in detail. The present review gives an insight with a better perspective for the scientific community for future studies devoted towards delimiting the mechanistic and structural basis of polyketide biosynthetic machinery vis-à-vis CHS.

Response of Mustard Microgreens to Different Wavelengths and Durations of UV-A LEDs

Ultraviolet A (UV-A) light-emitting diodes (LEDs) could serve as an effective tool for improving the content of health-promoting bioactive compounds in plants in controlled-environment agriculture (CEA) systems. The goal of this study was to investigate the effects of UV-A LEDs at different wavelengths (366, 390, and 402 nm) and durations (10 and 16 h) on the growth and phytochemical contents of mustard microgreens (Brassica juncea L. cv. "Red Lion"), when used as supplemental light to the main LED lighting system (with peak wavelengths of 447, 638, 665, and 731 nm). Plants were grown for 10 days under a total photon flux density (TPFD) of 300 µmol m^-2 s^-1 and 16-h light/8-h dark period. Different UV-A wavelengths and irradiance durations had varied effects on mustard microgreens. Supplemental UV-A radiation did not affect biomass accumulation; however, the longest UV-A wavelength (402 nm) increased the leaf area of mustard microgreens, regardless of the duration of irradiance. The concentration of the total phenolic content and α-tocopherol mostly increased under 402-nm UV-A, while that of nitrates increased under 366- and 390-nm UV-A at both radiance durations. The contents of lutein/zeaxanthin and β-carotene increased in response to the shortest UV-A wavelength (366 nm) at 10-h irradiance as well as longer UV-A wavelength (390 nm) at 16 h irradiance. The most positive effect on the accumulation of mineral elements, except iron, was observed under longer UV-A wavelengths at 16-h irradiance. Overall, these results suggest that properly composed UV-A LED parameters in LED lighting systems could improve the nutritional quality of mustard microgreens, without causing any adverse effects on plant growth.

Co-suppression of NbClpC1 and NbClpC2 alters plant morphology with changed hormone levels in Nicotiana benthamiana

KEY MESSAGE

Co-suppression of chaperonic ClpC1 and ClpC2 in Nicotiana benthamiana significantly affect the development and exogenous application of gibberellin partially rescue the developmental defects. Over the past decade, the Clp protease complex has been identified as being implicated in plastid protein quality control in plant cells. CLPC1 and CLPC2 proteins form the chaperone subunits of the Clp protease complex and unfold protein substrates to thread them into the ClpP complex. Here, using the technique of virus-induced gene silencing (VIGS), we suppressed both Nicotiana benthamiana ClpC1 and ClpC2 (NbClpC1/C2) functioning as chaperone subunits in the protease complex. Co-suppression of NbClpC1/C2 caused chlorosis and retarded-growth phenotype with no seed formation and significantly reduced root length. We found that co-suppression of NbClpC1/C2 also affected stomata and trichome formation and vascular bundle differentiation and patterning. Analysis of phytohormones revealed significant alteration and imbalance of major hormones in the leaves of NbClpC1/C2 co-suppressed plant. We also found that application of gibberellin (GA3) partially rescued the developmental defects. Co-suppression of NbClpC1/C2 significantly affected the development of N. benthamiana and exogenous application of GA3 partially rescued the developmental defects. Overall, our findings demonstrate that CLPC1 and CLPC2 proteins have a pivotal role in plant growth and development.

Short-Term Ultraviolet (UV)-A Light-Emitting Diode (LED) Radiation Improves Biomass and Bioactive Compounds of Kale

The aim of this study was to determine the influence of two types of UV-A LEDs on the growth and accumulation of phytochemicals in kale (Brassica oleracea var. acephala). Fourteen-day-old kale seedlings were transferred to a growth chamber and cultivated for 3 weeks. The kale plants were subsequently subjected to two types of UV-A LEDs (370 and 385 nm) of 30 W/m2 for 5 days. Growth characteristics were all significantly increased in plants exposed to UV-A LEDs, especially at the 385 nm level, for which dry weight of shoots and roots were significantly increased by 2.22 and 2.5 times, respectively, at 5 days of treatment. Maximum quantum efficiency of photosystem II photochemistry (Fv/Fm ratio) began to decrease after 3 h of treatment compared to the control. The total phenolic content of plants exposed to the two types of UV-A LEDs increased by 25% at 370 nm and 42% at 385 nm at 5 days of treatment, and antioxidant capacity also increased. The two types of UV-A LEDs also induced increasing contents of caffeic acid, ferulic acid, and kaempferol. The reactive oxygen species (ROS) temporarily increased in plants exposed to the two types of UV-A LEDs after 3 h of treatment. Moreover, transcript levels of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), and flavanone 3-hydroxylase (F3H) genes and PAL enzyme activity were higher in plants treated with UV-A LEDs. Our results suggested that short-term UV-A LEDs were effective in increasing growth and improving antioxidant phenolic compounds in kale, thereby representing a potentially effective strategy for enhancing the production of phytochemicals.

Preharvest and postharvest UV radiation affected flavonoid metabolism and antioxidant capacity differently in developing blueberries (Vaccinium corymbosum L.)

Flavonoids can protect plants against UV but the mechanism by which specific flavonoids during fruit development is unclear, especially in blueberries on living plants. We analyzed the gene expression and metabolite profiles of flavonols, proanthocyanidins (PAs), and anthocyanins under preharvest UV-B/-C and postharvest UV-A/-B/-C irradiation in developing blueberries. Both pre- and postharvest UV irradiation significantly increased flavonol accumulation during early fruit development, while increased anthocyanin and PA contents during late fruit development. However, PAs decreased during postharvest but increased during preharvest UV irradiation in green fruit. The antioxidant capacity increased by postharvest UV irradiation, while hardly affected by preharvest UV irradiation. Overall, the gene expression changes paralleled the flavonoid contents after UV irradiation. Notably, VcMYBPA1 was closely related with VcLAR and VcANR under pre- and postharvest UV irradiation, which could relate to PA biosynthesis. During natural fruit maturation and UV conditions, the elevated PA content exhibited higher potential antioxidant activity. Our results show that UV resistance is greater in living plants than detached fruits, the former showing a systemic and moderate response and the latter a non-systemic but strong response. These results might contribute to the development of pre- and postharvest technologies to promote healthier fruit consumption.

Current Review of the Modulatory Effects of LED Lights on Photosynthesis of Secondary Metabolites and Future Perspectives of Microgreen Vegetables

Light-emitting diode (LED) lights have recently been applied in controlled environment agriculture toward growing vegetables of various assortments, including microgreens. Spectral qualities of LED light on photosynthesis in microgreens are currently being studied for their ease of spectral optimization and high photosynthetic efficiency. This review aims to summarize the most recent discoveries and advances in specific phytochemical biosyntheses modulated by LED and other conventional lighting, to identify research gaps, and to provide future perspectives in this emerging multidisciplinary field of research and development. Specific emphasis was made on the effect of light spectral qualities on the biosynthesis of phenolics, carotenoids, and glucosinolates, as these phytochemicals are known for their antioxidant, anti-inflammatory effects, and many health benefits. Future perspectives on enhancing biosynthesis of these bioactives using the rapidly progressing LED light technology are further discussed.

Exploration of the effect of blue light on microRNAs involved in the accumulation of functional metabolites of longan embryonic calli through RNA-sequencing

BACKGROUND

The regulation of functional metabolites under light by structural genes and regulatory genes is understood but the roles of microRNAs in this pathway have rarely been reported and their regulation network is not yet clear.

RESULTS

Blue light was most conducive to promoting the synthesis of some functional metabolites in longan embryonic callus (ECs). In this study, we sequenced three small RNA libraries of constructed longan ECs under different light qualities (dark, blue, and white). A total of 29 and 22 miRNAs were differentially expressed in the dark versus blue (DB) and dark versus white (DW) combinations, respectively. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, most of the differentially expressed miRNA target genes were involved in plant hormone signal transduction, mitogen-activated protein kinase (MAPK) signaling, biosynthesis of unsaturated fatty acids, and so on. Cytoscape analysis of the target genes of miRNAs indicated that miR396b-5p and miR5139 had the most target genes in DB. Moreover, this study also found that miR171f_3 targeted DELLA, miR390e targeted BRI1, miR396b-5p targeted EBF1/2 and EIN3; these miRNAs participated in the blue light signaling network through their target genes and regulated the accumulation of longan functional metabolites.

CONCLUSIONS

The results of the study revealed that the expressions of phase-specific miRNAs vary with the change of functional metabolites in longan ECs. This study provides new insights into the molecular mechanisms that allow light to influence plant metabolism. © 2018 Society of Chemical Industry.

Plant Glutathione Transferases and Light

The activity and expression of glutathione transferases (GSTs) depend on several less-known endogenous and well-described exogenous factors, such as the developmental stage, presence, and intensity of different stressors, as well as on the absence or presence and quality of light, which to date have received less attention. In this review, we focus on discussing the role of circadian rhythm, light quality, and intensity in the regulation of plant GSTs. Recent studies demonstrate that diurnal regulation can be recognized in GST activity and gene expression in several plant species. In addition, the content of one of their co-substrates, reduced glutathione (GSH), also shows diurnal changes. Darkness, low light or shade mostly reduces GST activity, while high or excess light significantly elevates both the activity and expression of GSTs and GSH levels. Besides the light-regulated induction and dark inactivation of GSTs, these enzymes can also participate in the signal transduction of visible and UV light. For example, red light may alleviate the harmful effects of pathogens and abiotic stressors by increasing GST activity and expression, as well as GSH content in leaves of different plant species. Based on this knowledge, further research on plants (crops and weeds) or organs and temporal regulation of GST activity and gene expression is necessary for understanding the complex regulation of plant GSTs under various light conditions in order to increase the yield and stress tolerance of plants in the changing environment.

Segmental and tandem chromosome duplications led to divergent evolution of the chalcone synthase gene family in Phalaenopsis orchids

BACKGROUND AND AIMS

Orchidaceae is a large plant family, and its extraordinary adaptations may have guaranteed its evolutionary success. Flavonoids are a group of secondary metabolites that mediate plant acclimation to challenge environments. Chalcone synthase (CHS) catalyses the initial step in the flavonoid biosynthetic pathway. This is the first chromosome-level investigation of the CHS gene family in Phalaenopsis aphrodite and was conducted to elucidate if divergence of this gene family is associated with chromosome evolution.

METHODS

Complete CHS genes were identified from our whole-genome sequencing data sets and their gene expression profiles were obtained from our transcriptomic data sets. Fluorescence in situ hybridization (FISH) was conducted to position five CHS genes to high-resolution pachytene chromosomes.

KEY RESULTS

The five Phalaenopsis CHS genes can be classified into three groups, PaCHS1, PaCHS2 and the tandemly arrayed three-gene cluster, which diverged earlier than those of the orchid genera and species. Additionally, pachytene chromosome-based FISH mapping showed that the three groups of CHS genes are localized on three distinct chromosomes. Moreover, an expression analysis of RNA sequencing revealed that the five CHS genes had highly differentiated expression patterns and its expression pattern-based clustering showed high correlations between sequence divergences and chromosomal localizations of the CHS gene family in P. aphrodite.

CONCLUSIONS

Based on their phylogenetic relationships, expression clustering analysis and chromosomal distributions of the five paralogous PaCHS genes, we proposed that expansion of this gene family in P. aphrodite occurred through segmental duplications, followed by tandem duplications. These findings provide information for further studies of CHS functions and regulations, and shed light on the divergence of an important gene family in orchids.

Expression characterisation of cyclophilin BrROC1 during light treatment and abiotic stresses response in Brassica rapa subsp. rapa 'Tsuda'

ROC1 is a prototypic peptidyl prolyl cis/trans isomerase (PPIase) of the plant cytosol belonging to the large subfamily of cyclophilins that are associated with diverse functions through foldase, scaffolding, chaperoning or other unknown activities. Although many functions of plant cyclophilins have been reported, the molecular basis of stress-responsive expression of plant cyclophilins is still largely unknown. To characterise the roles of BrROC1 during light treatment and their responses in various abiotic stresses, we identified BrROC1 genes and characterised their expression patterns in Brassica rapa subsp. rapa 'Tsuda'. Our results showed that BrROC1 genes are multi-family genes. Transcript level analysis showed BrROC1-2 expressed higher than BrROC1-1 in 0 to 6-day-old seedlings under natural light. Moreover, BrROC1-2 genes were also induced to highly express in the cotyledon, upper hypocotyls and lower hypocotyls of seedlings under UV-A and blue-light treatment. In addition, the transcript level of BrROC1-1 was higher in pigment tissues than that in unpigment tissues (cotyledon and lower hypocotyl) under UV-A and blue-light treatment. Furthermore, when the unpigment epidermis (shaded light) of 2-month-old 'Tsuda' turnip roots was exposed to UV-A light, transcript levels of the BrROC1-1 and BrROC1-2 were significantly increased with time prolongation. These two BrROC1 genes might be involved in UV-A-induced anthocyanin synthesis in the root epidermis of 'Tsuda' turnip, which accumulates high levels of anthocyanin. These two BrROC1 genes were also induced to be regulated by abiotic stresses such as high or low temperature, dehydration, osmotic and salt stresses. Then, the results indicate that BrROC1 genes are involved in light induction response and may play important roles in adaptation of plants to various environmental stresses.

Transcriptional Activation of Anthocyanin Biosynthesis in Developing Fruit of Blueberries ( Vaccinium corymbosum L.) by Preharvest and Postharvest UV Irradiation

The effect and mechanism of preharvest and postharvest ultraviolet (UV) irradiation on anthocyanin biosynthesis during blueberry development were investigated. The results showed that preharvest UV-B,C and postharvest UV-A,B,C irradiation significantly promoted anthocyanin biosynthesis and the transcripts of late biosynthetic genes (LBG) VcDFR, VcANS, VcUFGT, and VcMYB transcription factor as well as DFR and UFGT activities in anthocyanin pathway in a UV wavelength- and developmental stage-dependent manner. VcMYB expression was positively correlated with that of VcANS and VcUFGT and coincided with anthocyanin biosynthesis responding to the UV radiation. Sugar decreased during postharvest but increased during preharvest UV radiation in mature fruit. Our results indicate that UV-responsive production of anthocyanins is mainly caused by the activation of anthocyanin downstream pathway genes, which could be upregulated by VcMYB. Furthermore, different potential response mechanisms may exist between preharvest and postharvest UV radiation in blueberries, involving a systemic response in living plants and a nonsystemic response in postharvest fruit.

Transcriptome analysis of radish sprouts hypocotyls reveals the regulatory role of hydrogen-rich water in anthocyanin biosynthesis under UV-A

BACKGROUND

Hydrogen gas (H2) is the most abundant element in the universe, and has been reported to act as a novel beneficial gaseous molecule in plant adaptive responses. Radish sprouts are popular because they contain substantial amounts of antioxidants and health-promoting compounds, such as anthocyanin and glucosinolates. Although radish sprouts accumulated more anthocyanin under UV-A after treatment with hydrogen-rich water (HRW), the molecular mechanism responsible is still elusive. To explore these mechanisms, RNA-seq analysis was used.

RESULTS

Four cDNA libraries from radish sprout hypocotyls were constructed, and a total of 14,564 differentially expressed genes (DEGs) were identified through pairwise comparisons. By Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, these unigenes were found to be implicated in light signal perception and transduction, starch and sucrose metabolism, photosynthesis, nitrogen metabolism and biosynthesis of secondary metabolites. The MYB-bHLH-WD40 complex accounted for the majority of the transcription factors found to be involved in anthocyanin biosynthesis, and levels of transcripts for this complex were in accordance with the anthocyanin concentrations observed. In addition, other transcription factors (such as NAC, bZIP and TCP) might participate in HRW-promoted anthocyanin biosynthesis. Furthermore, the signaling processes of plant hormones, MAPKs and Ca2+ might be involved in HRW-promoted anthocyanin biosynthesis under UV-A. The expression patterns of 16 selected genes were confirmed using qRT-PCR analysis.

CONCLUSIONS

Taken together, the results of this study may expand our understanding of HRW-promoted anthocyanin accumulation under UV-A in radish sprouts.

Crystal structure and enzymatic properties of chalcone isomerase from the Antarctic vascular plant Deschampsia antarctica Desv

Chalcone isomerase (CHI) is an important enzyme for flavonoid biosynthesis that catalyzes the intramolecular cyclization of chalcones into (S)-flavanones. CHIs have been classified into two types based on their substrate specificity. Type I CHIs use naringenin chalcone as a substrate and are found in most of plants besides legumes, whereas type II CHIs in leguminous plants can also utilize isoliquiritigenin. In this study, we found that the CHI from the Antarctic plant Deschampsia antarctica (DaCHI1) is of type I based on sequence homology but can use type II CHI substrates. To clarify the enzymatic mechanism of DaCHI1 at the molecular level, the crystal structures of unliganded DaCHI1 and isoliquiritigenin-bound DaCHI1 were determined at 2.7 and 2.1 Å resolutions, respectively. The structures revealed that isoliquiritigenin binds to the active site of DaCHI1 and induces conformational changes. Additionally, the activity assay showed that while DaCHI1 exhibits substrate preference for naringenin chalcone, it can also utilize isoliquiritigenin although the catalytic activity was relatively low. Based on these results, we propose that DaCHI1 uses various substrates to produce antioxidant flavonoids as an adaptation to oxidative stresses associated with harsh environmental conditions.

The influence of postharvest UV-C treatment on anthocyanin biosynthesis in fresh-cut red cabbage

Red cabbage (Brassica oleracea L. var. capitata f. rubra DC.) is a fresh edible vegetable consumed globally that contains high levels of antioxidant compounds including anthocyanins. In this study, fresh-cut red cabbage was treated with different Ultraviolet-C (UV-C) dosages. Fifteen cyanidin derivatives were observed in UV-C treated fresh-cut red cabbage; four of these were anthocyanins absent in control samples. The optimum dose of UV-C for enhancing total anthocyanin content in fresh-cut red cabbage was 3.0 kJ/m². Different UV-C irradiation doses resulted in miscellaneous responses for each of the anthocyanin compounds, and these alterations appeared to be dose-dependent. The expression of genes relating to anthocyanin metabolism was altered by UV-C irradiation. For example, genes for biosynthetic enzymes including glycosyltransferase and acyltransferase, as well as R2R3 MYB transcription factors (production of anthocyanin pigment 1 and MYB114), had strongly increased expression following UV-C treatment. These results are in accord with the roles of these gene products in anthocyanin metabolism. This is, to the authors’ knowledge, the first report demonstrating that UV-C treatment can increase the antioxidant activity in fresh-cut red cabbage in storage. Moreover, our detailed phytochemical and gene expression analysis establish specific roles for both anthocyanins and metabolism genes in this process.

Identification of Light-Independent Anthocyanin Biosynthesis Mutants Induced by Ethyl Methane Sulfonate in Turnip "Tsuda" (Brassica rapa)

The epidermis of swollen storage roots in purple cultivars of turnip “Tsuda” (Brassica rapa) accumulates anthocyanin in a light-dependent manner, especially in response to UV-A light, of which the mechanism is unclear. In this study, we mutagenized 15,000 seeds by 0.5% (v/v) ethyl methane sulfonate (EMS) and obtained 14 mutants with abnormal anthocyanin production in their epidermis of swollen storage roots. These mutants were classified into two groups: the red mutants with constitutive anthocyanin accumulation in their epidermis of storage roots even in underground parts in darkness and the white mutants without anthocyanin accumulation in the epidermis of storage roots in aboveground parts exposed to sunlight. Test cross analysis demonstrated that w9, w68, w204, r15, r21, r30 and r57 contained different mutations responsible for their phenotypic variations. Further genetic analysis of four target mutants (w9, w68, w204 and r15) indicated that each of them was controlled by a different recessive gene. Intriguingly, the expression profiles of anthocyanin biosynthesis genes, including structural and regulatory genes, coincided with their anthocyanin levels in the epidermis of storage roots in the four target mutants. We proposed that potential genes responsible for the mutations should be upstream factors of the anthocyanin biosynthesis pathway in turnips, which provided resources to further investigate the mechanisms of light-induced anthocyanin accumulation.

Interactive Effects of UV-B Light with Abiotic Factors on Plant Growth and Chemistry, and Their Consequences for Defense against Arthropod Herbivores

Ultraviolet-B (UV-B) light plays a crucial role in plant-herbivorous arthropods interactions by inducing changes in constitutive and inducible plant defenses. In particular, constitutive defenses can be modulated by UV-B-induced photomorphogenic responses and changes in the plant metabolome. In accordance, the prospective use of UV-B light as a tool to increase plant protection in agricultural practice has gained increasing interest. Changes in the environmental conditions might, however, modulate the UV-B -induced plant responses. While in some cases plant responses to UV-B can increase adaptation to changes in certain abiotic factors, UV-B-induced responses might be also antagonized by the changing environment. The outcome of these interactions might have a great influence on how plants interact with their enemies, e.g., herbivorous arthropods. Here, we provide a review on the interactive effects of UV-B and light quantity and quality, increased temperature and drought stress on plant biochemistry, and we discuss the implications of the outcome of these interactions for plant resistance to arthropod pests.

Effects of Tibetan turnip (Brassica rapa L.) on promoting hypoxia-tolerance in healthy humans

ETHNOPHARMACOLOGICAL RELEVANCE

Tibetan turnip (Brassica rapa L.), widely distributed in Tibet region, is an edible and medical plant with effects of "tonic and anti-hypoxia" "heat-clearing and detoxification" and "alleviating fatigue" according to traditional Tibetan medical books.

AIM OF THE STUDY

This research systematically studied the effects of Tibetan turnip on promoting hypoxia-tolerance in humans and the mechanisms.

MATERIALS AND METHODS

A 7-d, self-control and single-blind human feeding trial was conducted among 27 healthy subjects with 8 males and 10 females in feeding group fed with 7.5g turnip powder 2 times daily while 4 males and 5 females in control group fed with 7.5g radish powder twice a day. Subjects were required to undergo a hypoxia tolerance test (7.1% O₂) and a cardiopulmonary function evaluation (Bruce treadmill protocol) before (1st day) and after (9th day) the trial. Simultaneously, the anti-oxidative activities (SOD, CAT, GSH-Px, MDA), routine and biochemical analyses of blood samples were evaluated.

RESULTS

The females' SpO₂ increased significantly by 6.4% at the end of the hypoxia tolerance test after taking turnips (p<0.05), and the hypoxia symptoms in most of the subjects were alleviated as well. The anaerobic threshold, peak O₂ pulse and peak VO₂/kg were significantly improved after 7-d turnip consumption during the Bruce treadmill test (p<0.05). As for the blood analysis, anti-oxidative activities were boosted effectively after the 7-d treatments. Moreover, mean corpuscular hemoglobin concentration (MCHC) in the males of feeding group increased significantly (p<0.05). However, little changes of all variables were observed in the control group.

CONCLUSIONS

Consumption of Tibetan turnips for 7 days likely contributed to the hypoxia tolerance in healthy humans, which could be due to its abilities of improving oxygen uptake and delivery, enhancing body antioxidant capacity and increasing MCHC. However, further studies with larger samples and double-blind design are warranted, and future studies covering more diverse populations (unhealthy, athletic) would be also considered. Moreover, researches on identifying Tibetan turnip's active compounds are desired as well.

The acyl-activating enzyme PhAAE13 is an alternative enzymatic source of precursors for anthocyanin biosynthesis in petunia flowers

Anthocyanins, a class of flavonoids, are responsible for the orange to blue coloration of flowers and act as visual attractors to aid pollination and seed dispersal. Malonyl-CoA is the precursor for the formation of flavonoids and anthocyanins. Previous studies have suggested that malonyl-CoA is formed almost exclusively by acetyl-CoA carboxylase, which catalyzes the ATP-dependent formation of malonyl-CoA from acetyl-CoA and bicarbonate. In the present study, the full-length cDNA of Petunia hybrida acyl-activating enzyme 13 (PhAAE13), a member of clade VII of the AAE superfamily that encodes malonyl-CoA synthetase, was isolated. The expression of PhAAE13 was highest in corollas and was down-regulated by ethylene. Virus-induced gene silencing of petunia PhAAE13 significantly reduced anthocyanin accumulation, fatty acid content, and cuticular wax components content, and increased malonic acid content in flowers. The silencing of PhAAE3 and PhAAE14, the other two genes in clade VII of the AAE superfamily, did not change the anthocyanin content in petunia flowers. This study provides strong evidence indicating that PhAAE13, among clade VII of the AAE superfamily, is specifically involved in anthocyanin biosynthesis in petunia flowers.

Response and Defense Mechanisms of Taxus chinensis Leaves Under UV-A Radiation are Revealed Using Comparative Proteomics and Metabolomics Analyses

Taxus chinensis var. mairei is a species endemic to south-eastern China and one of the natural sources for the anticancer medicine paclitaxel. To investigate the molecular response and defense mechanisms of T. chinensis leaves to enhanced ultraviolet-A (UV-A) radiation, gel-free/label-free and gel-based proteomics and gas chromatography-mass spectrometry (GC-MS) analyses were performed. The transmission electron microscopy results indicated damage to the chloroplast under UV-A radiation. Proteomics analyses in leaves and chloroplasts showed that photosynthesis-, glycolysis-, secondary metabolism-, stress-, and protein synthesis-, degradation- and activation-related systems were mainly changed under UV-A radiation. Forty-seven PSII proteins and six PSI proteins were identified as being changed in leaves and chloroplasts under UV-A treatment. This indicated that PSII was more sensitive to UV-A than PSI as the target of UV-A light. Enhanced glycolysis, with four glycolysis-related key enzymes increased, provided precursors for secondary metabolism. The 1-deoxy-d-xylulose-5-phosphate reductoisomerase and 4-hydroxy-3-methylbut-2-enyl diphosphate reductase were identified as being significantly increased during UV-A radiation, which resulted in paclitaxel enhancement. Additionally, mRNA expression levels of genes involved in the paclitaxel biosynthetic pathway indicated a down-regulation under UV-A irradiation and up-regulation in dark incubation. These results reveal that a short-term high dose of UV-A radiation could stimulate the plant stress defense system and paclitaxel production.

Exploring miRNAs involved in blue/UV-A light response in Brassica rapa reveals special regulatory mode during seedling development

BACKGROUND

Growth, development, and pigment synthesis in Brassica rapa subsp. rapa cv. Tsuda, a popular vegetable crop, are influenced by light. Although microRNAs (miRNAs) have vital roles in the metabolic processes and abiotic stress responses of plants, whether miRNAs play a role in anthocyanin biosynthesis and development of Tsuda seedlings exposed to light is unknown.

RESULTS

Seventeen conserved and 226 novel miRNAs differed at least 2-fold in response to blue and UV-A light compared with levels after a dark treatment. Real time PCR showed that BrmiR159, BrmiRC0191, BrmiRC0460, BrmiRC0323, BrmiRC0418, BrmiRC0005 were blue light-induced and northern blot revealed that the transcription level of BrmiR167 did not differ significantly among seedlings treated with dark, blue or UV-light. BrmiR156 and BrmiR157 were present in the greatest amount (number of reads) and among their 8 putative targets in the SPL gene family, only SPL9 (Bra004674) and SPL15 (Bra003305) increased in expression after blue or UV-A exposure. In addition, miR157-guided cleavage of target SPL9 mRNAs (Bra004674, Bra016891) and SPL15 mRNAs (Bra003305, Bra014599) took place 10 or 11 bases from the 5' ends of the binding region in the miR157 sequence.

CONCLUSIONS

A set of miRNAs and their targets involved in the regulation of the light-induced photomorphogenic phenotype in seedlings of Brassica rapa was identified, providing new insights into blue and UV-A light-responsive miRNAs in seedlings of Tsuda and evidence of multiple targets for the miRNAs and their diverse roles in plant development.

Chalcone synthase genes from milk thistle (Silybum marianum): isolation and expression analysis

Silymarin is a flavonoid compound derived from milk thistle (Silybum marianum) seeds which has several pharmacological applications. Chalcone synthase (CHS) is a key enzyme in the biosynthesis of flavonoids; thereby, the identification of CHS encoding genes in milk thistle plant can be of great importance. In the current research, fragments of CHS genes were amplified using degenerate primers based on the conserved parts of Asteraceae CHS genes, and then cloned and sequenced. Analysis of the resultant nucleotide and deduced amino acid sequences led to the identification of two different members of CHS gene family,SmCHS1 and SmCHS2. Third member, full-length cDNA (SmCHS3) was isolated by rapid amplification of cDNA ends (RACE), whose open reading frame contained 1239 bp including exon 1 (190 bp) and exon 2 (1049 bp), encoding 63 and 349 amino acids, respectively. In silico analysis of SmCHS3 sequence contains all the conserved CHS sites and shares high homology with CHS proteins from other plants.Real-time PCR analysis indicated that SmCHS1 and SmCHS3 had the highest transcript level in petals in the early flowering stage and in the stem of five upper leaves, followed by five upper leaves in the mid-flowering stage which are most probably involved in anthocyanin and silymarin biosynthesis.

Molecular progress in research on fruit astringency

Astringency is one of the most important components of fruit oral sensory quality. Astringency mainly comes from tannins and other polyphenolic compounds and causes the drying, roughening and puckering of the mouth epithelia attributed to the interaction between tannins and salivary proteins. There is growing interest in the study of fruit astringency because of the healthy properties of astringent substances found in fruit, including antibacterial, antiviral, anti-inflammatory, antioxidant, anticarcinogenic, antiallergenic, hepatoprotective, vasodilating and antithrombotic activities. This review will focus mainly on the relationship between tannin structure and the astringency sensation as well as the biosynthetic pathways of astringent substances in fruit and their regulatory mechanisms.

Monochromatic light increases anthocyanin content during fruit development in bilberry

BACKGROUND

Light is one of the most significant environmental factors affecting to the accumulation of flavonoids in fruits. The composition of the light spectrum has been shown to affect the production of phenolic compounds during fruit ripening. However, specific information on the biosynthesis of flavonoids in fruits in response to different wavelengths of light is still scarce. In the present study bilberry (Vaccinium myrtillus L.) fruits, which are known to be rich with anthocyanin compounds, were illuminated with blue, red, far-red or white light during the berry ripening process. Following the illumination, the composition of anthocyanins and other phenolic compounds was analysed at the mature ripening stage of fruits.

RESULTS

All the three monochromatic light treatments had significant positive effect on the accumulation of total anthocyanins in ripe fruits compared to treatment with white light or plants kept in darkness. The elevated levels of anthocyanins were mainly due to a significant increase in the accumulation of delphinidin glycosides. A total of 33 anthocyanin compounds were detected in ripe bilberry fruits, of which six are novel in bilberry (cyanidin acetyl-3-O-galactose, malvidin acetyl-3-O-galactose, malvidin coumaroyl-3-O-galactose, malvidin coumaroyl-3-O-glucose, delphinidin coumaroyl-3-O-galactose, delphinidin coumaroyl-3-O-glucose).

CONCLUSIONS

Our results indicate that the spectral composition of light during berry development has significant effect on the flavonoid composition of ripe bilberry fruits.

BrMYB4, a suppressor of genes for phenylpropanoid and anthocyanin biosynthesis, is down-regulated by UV-B but not by pigment-inducing sunlight in turnip cv. Tsuda

The regulation of light-dependent anthocyanin biosynthesis in Brassica rapa subsp. rapa cv. Tsuda turnip was investigated using an ethyl methanesulfonate (EMS)-induced mutant R30 with light-independent pigmentation. TILLING (targeting induced local lesions in genomes) and subsequent analysis showed that a stop codon was inserted in the R2R3-MYB transcription factor gene BrMYB4 and that the encoded protein (BrMYB4mu) had lost its C-terminal region. In R30, anthocyanin accumulated in the below-ground portion of the storage root of 2-month-old plants. In 4-day-old seedlings and 2-month-old plants, expression of BrMYB4 was similar between R30 and the wild type (WT), but the expression of the cinnamate 4-hydroxylase gene (BrC4H) was markedly enhanced in R30 in the dark. In turnip seedlings, BrMYB4 expression was suppressed by UV-B irradiation in the WT, but this negative regulation was absent in R30. Concomitantly, BrC4H was repressed by UV-B irradiation in the WT, but stayed at high levels in R30. A gel-shift assay revealed that BrMYB4 could directly bind to the promoter region of BrC4H, but BrMYB4mu could not. The BrMYB4-enhanced green fluorescent protein (eGFP) protein could enter the nucleus in the presence of BrSAD2 (an importin β-like protein) nuclear transporter, but BrMYB4mu-eGFP could not. These results showed that BrMYB4 functions as a negative transcriptional regulator of BrC4H and mediates UV-B-dependent phenylpropanoid biosynthesis, while BrMYB4mu has lost this function. In the storage roots, the expression of anthocyanin biosynthesis genes was enhanced in R30 in the dark and in sunlight in both the WT and R30. However, in the WT, anthocyanin-inducing sunlight did not suppress BrMYB4 expression. Therefore, sunlight-induced anthocyanin biosynthesis does not seem to be regulated by BrMYB4.

Genome-wide transcriptional profiles of the berry skin of two red grape cultivars (Vitis vinifera) in which anthocyanin synthesis is sunlight-dependent or -independent

Global gene expression was analyzed in the berry skin of two red grape cultivars, which can ('Jingyan') or cannot ('Jingxiu') synthesize anthocyanins after sunlight exclusion from fruit set until maturity. Gene transcripts responding to sunlight exclusion in 'Jingyan' were less complex than in 'Jingxiu'; 528 genes were induced and 383 repressed in the former, whereas 2655 genes were induced and 205 suppressed in 'Jingxiu'. They were regulated either in the same or opposing manner in the two cultivars, or in only one cultivar. In addition to VvUFGT and VvMYBA1, some candidate genes (e.g. AOMT, GST, and ANP) were identified which are probably involved in the differential responses of 'Jingxiu' and 'Jingyan' to sunlight exclusion. In addition, 26 MYB, 14 bHLH and 23 WD40 genes responded differently to sunlight exclusion in the two cultivars. Interestingly, all of the 189 genes classified as being relevant to ubiquitin-dependent protein degradation were down-regulated by sunlight exclusion in 'Jingxiu', but the majority (162) remained unchanged in 'Jingyan' berry skin. It would be of interest to determine the precise role of the ubiquitin pathway following sunlight exclusion, particularly the role of COP9 signalosome, cullins, RING-Box 1, and COP1-interacting proteins. Only a few genes in the light signal system were found to be regulated by sunlight exclusion in either or both cultivars. This study provides a valuable overview of the transcriptome changes and gives insight into the genetic background that may be responsible for sunlight-dependent versus -independent anthocyanin biosynthesis in berry skin.

Effect of low-intensity white light mediated de-etiolation on the biosynthesis of polyphenols in tea seedlings

Light is an important source of energy as well as environmental signal for the regulation of biosynthesis and accumulation of multiple secondary metabolites in plants. Polyphenols are the major class of secondary metabolites in tea, which possess potential antioxidant properties. In order to investigate the effect of light signal on the regulation of biosynthesis and accumulation of polyphenols in tea seedlings, a low-intensity white light was used and the change in trends of polyphenol contents, patterns of gene expression, and corresponding enzymatic activities were studied. LC-TOF/MS analysis revealed that light signal promoted the accumulation of hydroxycinnamic acid derivatives and nongalloylated catechin (EGC), while it restrained the accumulation of β-glucogallin and galloylated catechins. The quantitative reverse transcription-PCR analysis showed that the expression levels of the regulator genes and some structural genes involved in photomorphogenesis and biosynthetic pathway of nongalloylated catechins, respectively, were up-regulated. In contrast, the expression of DHD/SDH and UGT genes, which may be involved in biosynthetic pathway of βG, was down-regulated. The corresponding in vitro enzyme assays revealed decrease in the activity of ECGT (galloylates nongalloylated catechins) and an increase in activity of GCH (hydrolyzes galloylated catechins) during de-etiolation. The present study yielded inconsistent accumulation patterns of phenolic acids, flavan-3-ols, and flavonols in tea seedlings during de-etiolation. In addition, the accumulation of catechins was possibly jointly influenced by the biosynthesis, hydrolysis, glycosylation, and galloylation of polyphenols in tea plants.

Ultraviolet-B radiation modifies the quantitative and qualitative profile of flavonoids and amino acids in grape berries

Grapevine cv. Tempranillo fruit-bearing cuttings were exposed to supplemental ultraviolet-B (UV-B) radiation under controlled conditions, in order to study its effect on grape traits, ripening, amino acids and flavonoid profile. The plants were exposed to two doses of UV-B biologically effective (5.98 and 9.66kJm(-2)d(-1)), applied either from fruit set to ripeness or from the onset of veraison to ripeness. A 0kJm(-2)d(-1) treatment was included as a control. UV-B did not significantly modify grape berry size, but increased the relative mass of berry skin. Time to reach ripeness was not affected by UV-B, which may explain the lack of changes in technological maturity. The concentration of must extractable anthocyanins, colour density and skin flavonols were enhanced by UV-B, especially in plants exposed from fruit set. The quantitative and qualitative profile of grape skin flavonols were modified by UV-B radiation. Monosubstituted flavonols relative abundance increased proportionally to the accumulated UV-B doses. Furthermore, trisubstituted forms, which where predominant in non-exposed berries, were less abundant as UV-B exposure increased. Although total free amino acid content remained unaffected by the treatments, the increased levels of gamma-aminobutyric acid (GABA), as well as the decrease in threonine, isoleucine, methionine, serine and glycine, revealed a potential influence of UV-B on the GABA-mediated signalling and amino acid metabolism. UV-B had an overall positive impact on grape berry composition.

Sequential light programs shape kale (Brassica napus) sprout appearance and alter metabolic and nutrient content

Different light wavelengths have specific effects on plant growth and development. Narrow-bandwidth light-emitting diode (LED) lighting may be used to directionally manipulate size, color and metabolites in high-value fruits and vegetables. In this report, Red Russian kale (Brassica napus) seedlings were grown under specific light conditions and analyzed for photomorphogenic responses, pigment accumulation and nutraceutical content. The results showed that this genotype responds predictably to darkness, blue and red light, with suppression of hypocotyl elongation, development of pigments and changes in specific metabolites. However, these seedlings were relatively hypersensitive to far-red light, leading to uncharacteristically short hypocotyls and high pigment accumulation, even after growth under very low fluence rates (<1 μmol m(-2) s(-1)). General antioxidant levels and aliphatic glucosinolates are elevated by far-red light treatments. Sequential treatments of darkness, blue light, red light and far-red light were applied throughout sprout development to alter final product quality. These results indicate that sequential treatment with narrow-bandwidth light may be used to affect key economically important traits in high-value crops.

Light-controlled flavonoid biosynthesis in fruits

Light is one of the most important environmental factors affecting flavonoid biosynthesis in plants. The absolute dependency of light to the plant development has driven evolvement of sophisticated mechanisms to sense and transduce multiple aspects of the light signal. Light effects can be categorized in photoperiod (duration), intensity (quantity), direction and quality (wavelength) including UV-light. Recently, new information has been achieved on the regulation of light-controlled flavonoid biosynthesis in fruits, in which flavonoids have a major contribution on quality. This review focuses on the effects of the different light conditions on the control of flavonoid biosynthesis in fruit producing plants. An overview of the currently known mechanisms of the light-controlled flavonoid accumulation is provided. R2R3 MYB transcription factors are known to regulate by differential expression the biosynthesis of distinct flavonoids in response to specific light wavelengths. Despite recent advances, many gaps remain to be understood in the mechanisms of the transduction pathway of light-controlled flavonoid biosynthesis. A better knowledge on these regulatory mechanisms is likely to be useful for breeding programs aiming to modify fruit flavonoid pattern.

Light-controlled flavonoid biosynthesis in fruits

Light is one of the most important environmental factors affecting flavonoid biosynthesis in plants. The absolute dependency of light to the plant development has driven evolvement of sophisticated mechanisms to sense and transduce multiple aspects of the light signal. Light effects can be categorized in photoperiod (duration), intensity (quantity), direction and quality (wavelength) including UV-light. Recently, new information has been achieved on the regulation of light-controlled flavonoid biosynthesis in fruits, in which flavonoids have a major contribution on quality. This review focuses on the effects of the different light conditions on the control of flavonoid biosynthesis in fruit producing plants. An overview of the currently known mechanisms of the light-controlled flavonoid accumulation is provided. R2R3 MYB transcription factors are known to regulate by differential expression the biosynthesis of distinct flavonoids in response to specific light wavelengths. Despite recent advances, many gaps remain to be understood in the mechanisms of the transduction pathway of light-controlled flavonoid biosynthesis. A better knowledge on these regulatory mechanisms is likely to be useful for breeding programs aiming to modify fruit flavonoid pattern.

Physiological factors affecting transcription of genes involved in the flavonoid biosynthetic pathway in different rice varieties

Flavonoids play an important role in the grain color and flavor of rice. Since their characterization in maize, the flavonoid biosynthetic genes have been extensively studied in grape, Arabidopsis, and Petunia. However, we are still a long way from understanding the molecular features and mechanisms underlying the flavonoid biosynthetic pathway. The present study was undertaken to understand the physiological factors affecting the transcription and regulation of these genes. We report that the expression of CHI, CHS, DFR, LAR, and ANS, the 5 flavonoid biosynthetic genes in different rice varieties, differ dramatically with respect to the stage of development, white light, and sugar concentrations. We further demonstrate that white light could induce the transcription of the entire flavonoid biosynthetic gene pathway; however, differences were observed in the degrees of sensitivity and the required illumination time. Our study provides valuable insights into understanding the regulation of the flavonoid biosynthetic pathway.

Chalcone synthase family genes have redundant roles in anthocyanin biosynthesis and in response to blue/UV-A light in turnip (Brassica rapa; Brassicaceae)

PREMISE OF THE STUDY

The epidermis of Brassica rapa (turnip) cv. Tsuda contains light-induced anthocyanins, visible signs of activity of chalcone synthase (CHS), a key anthocyanin biosynthetic enzyme, which is encoded by the CHS gene family. To elucidate the regulation of this light-induced pigmentation, we isolated Brassica rapa CHS1-CHS6 (BrCHS1-CHS6) and characterized their cis-elements and expression patterns.

METHODS

Epidermises of light-exposed swollen hypocotyls (ESHS) were harvested to analyze transcription levels of BrCHS genes by real-time PCR. Different promoters for the genes were inserted into tobacco to examine pCHS-GUS activity by histochemistry. Yeast-one-hybridization was used to detect binding activity of BrCHS motifs to transcription factors.

KEY RESULTS

Transcript levels of BrCHS1, -4, and -5 and anthocyanin-biosynthesis-related genes F3H, DFR, and ANS were high, while those of BrCHS2, -3, and -6 were almost undetectable in pigmented ESHS. However, in leaves, CHS5, F3H, and ANS expression was higher than in nonpigmented ESHS, but transcription of DFR was not detected. In the analysis of BrCHS1 and BrCHS3 promoter activity, GUS activity was strong in pigmented flowers of BrPCHS1-GUS-transformed tobacco plants, but nearly absent in BrPCHS3-GUS-transformed plants. Transcript levels of regulators, BrMYB75 and BrTT8, were strongly associated with the anthocyanin content and were light-induced. Coregulated cis-elements were found in promoters of BrCHS1,-4, and -5, and BrMYB75 and BrTT8 had high binding activities to the BrCHS Unit 1 motif.

CONCLUSIONS

The chalcone synthase gene family encodes a redundant set of light-responsive, tissue-specific genes that are expressed at different levels and are involved in flavonoid biosynthesis in Tsuda turnip.

Phototropin 2 is involved in blue light-induced anthocyanin accumulation in Fragaria x ananassa fruits

Anthocyanins are widespread, essential secondary metabolites in higher plants during color development in certain flowers and fruits. In strawberries, anthocyanins are also key contributors to fruit antioxidant capacity and nutritional value. However, the effects of different light qualities on anthocyanin accumulation in strawberry (Fragaria x ananassa, cv. Sachinoka) fruits remain elusive. In the present study, we showed the most efficient increase in anthocyanin content occurred by blue light irradiation. Light sensing at the molecular level was investigated by isolation of two phototropin (FaPHOT1 and FaPHOT2), two cryptochrome (FaCRY1 and FaCRY2), and two phytochrome (FaPHYA and FaPHYB) homologs. Expression analysis revealed only FaPHOT2 transcripts markedly increased depending on fruit developmental stage, and a corresponding increase in anthocyanin content was detected. FaPHOT2 knockdown resulted in decreased anthocyanin content; however, overexpression increased anthocyanin content. These findings suggested blue light induced anthocyanin accumulation, and FaPHOT2 may play a role in sensing blue light, and mediating anthocyanin biosynthesis in strawberry fruits. This is the first report to find a relationship between visible light sensing, and color development in strawberry fruits.

Transcriptional activation of flavan-3-ols biosynthesis in grape berries by UV irradiation depending on developmental stage

The accumulation of flavan-3-ols in response to ultraviolet (UV) irradiation was investigated in grape berries with emphasis on the expression of three structural genes (VvANR, VvLAR1 and VvLAR2), and three regulatory genes (VvMYB5a, VvMYB5b and VvMYBPA1), and as well as the contents of flavan-3-ols. UV-A irradiation showed a promoting effect on the transcription of three structural genes at 3-week (flavan-3-ol accumulation period), 7-week (the end of flavan-3-ol accumulation) and 11-week (the beginning of anthocyanin synthesis) periods of berry development. UV-B irradiation also up-regulated all or part of the structural genes, but the activation effect of UV-C irradiation appeared only in the 7-week and 11-week grapes. The developmental stage-dependent activation by the three types of UV was also initiated for three regulatory genes, but the transcriptional up-regulation of the structural genes by UV irradiation was not entirely regulated by these transcription factors. The increase in the content of 2,3-trans-flavan-3-ols or 2,3-cis-flavan-3-ols by UV irradiation paralleled overall with the expression up-regulation of their corresponding structural genes in the 3-week and the 7-week grapes, but not in the 11-week grapes, indicating that the overexpression of structural genes by UV radiation does not translate into a higher content of flavan 3-ols at mature stage.

Increase in the Contents of Ginsenosides in Raw Ginseng Roots in Response to Exposure to 450 and 470 nm Light from Light-Emitting Diodes

An light-emitting diode (LED)-based light source was used as a monochromatic light source to determine the responses of raw ginseng roots (Panax ginseng Meyer) to specific emission spectra with respect to the production of ginsenosides. The ginsenoside content in the ginseng roots changed in response to the LED light treatments at 25℃ relative to the levels in the control roots that were treated in the dark or at 4℃ for 7 d. Ginseng roots were exposed to LEDs with four different peak emission wavelengths, 380, 450, 470, and 660 nm, in closed compartments. Compared with the control 4℃-treated roots, roots that were treated with 450 and 470 nm light showed a significantly increased production of ginsenosides (p<0.05), with increases of 64.9% and 74.1%, respectively. The contents of the ginsenosides Rb₂, Rc, and Rg₁ were significantly higher (p<0.05) in the 450 and 470 nm-treated root samples. The ratio of protopanaxadiol ginsenosides (Rb₁, Rb₂, Rc, and Rd) to protopanaxatriol ginsenosides (Rg₁, Rg₂, Re, and Rf) was significantly higher (p<0.05) in the 450 and 470 nm-treated root samples than in the control 4℃-treated roots. This is the first report that demonstrates the increase and conversion of ginsenosides in raw ginseng roots in response to exposure to LED light.

Striking natural diversity in glandular trichome acylsugar composition is shaped by variation at the Acyltransferase2 locus in the wild tomato Solanum habrochaites

Acylsugars are polyesters of short- to medium-length acyl chains on sucrose or glucose backbones that are produced in secretory glandular trichomes of many solanaceous plants, including cultivated tomato (Solanum lycopersicum). Despite their roles in biotic stress adaptation and their wide taxonomic distribution, there is relatively little information about the diversity of these compounds and the genes responsible for their biosynthesis. In this study, acylsugar diversity was assessed for 80 accessions of the wild tomato species Solanum habrochaites from throughout the Andes Mountains. Trichome metabolites were analyzed by liquid chromatography-time of flight-mass spectrometry, revealing the presence of at least 34 structurally diverse acylsucroses and two acylglucoses. Distinct phenotypic classes were discovered that varied based on the presence of glucose or sucrose, the numbers and lengths of acyl chains, and the relative total amounts of acylsugars. The presence or absence of an acetyl chain on the acylsucrose hexose ring caused clustering of the accessions into two main groups. Analysis of the Acyltransferase2 gene (the apparent ortholog of Solyc01g105580) revealed differences in enzyme activity and gene expression correlated with polymorphism in S. habrochaites accessions that varied in acylsucrose acetylation. These results are consistent with the hypothesis that glandular trichome acylsugar acetylation is under selective pressure in some populations of S. habrochaites and that the gene mutates to inactivity in the absence of selection.