Sugar-Dependent Expression of the CHS-A Gene for Chalcone Synthase from Petunia in Transgenic Arabidopsis

Total Flavonoid Contents and the Expression of Flavonoid Biosynthetic Genes in Breadfruit (Artocarpus altilis) Scions Growing on Lakoocha (Artocarpus lakoocha) Rootstocks

Breadfruit (Artocarpus altilis) is a traditional fruit tree of 15-30 m height in the tropics. The presence of size-controlling rootstock in the species is not known. A small tropical tree species, lakoocha (Artocarpus lakoocha), was recently identified as a potential vigor-controlling rootstock, conferring over a 65% reduction in breadfruit tree height. To better understand the intriguing scion/rootstock interactions involved in dwarfing, we investigate flavonoid accumulation and its regulation in breadfruit scions in response to different rootstocks. To this end, we isolated a chalcone synthase cDNA, AaCHS, and a full-length bifunctional dihydroflavonol 4-reductase cDNA, AaDFR, from breadfruit scion stems. The expression of both AaCHS and AaDFR genes was examined over the period of 16 to 24 months following grafting. During the development of the dwarf phenotype, breadfruit scion stems on lakoocha rootstocks display significant increases in total flavonoid content, and show upregulated AaCHS expression when compared with those on self-grafts and non-grafts. There is a strong, positive correlation between the transcript levels of AaCHS and total flavonoid content in scion stems. The transcript levels of AaDFR are not significantly different across scions on different rootstocks. This work provides insights into the significance of flavonoid biosynthesis in rootstock-induced breadfruit dwarfing.

Combined Metabolome and Transcriptome Analysis Elucidates Sugar Accumulation in Wucai (Brassica campestris L.)

Wucai (Brassica campestris L.) is a leafy vegetable that originated in China, its soluble sugars accumulate significantly to improve taste quality during maturation, and it is widely accepted by consumers. In this study, we investigated the soluble sugar content at different developmental stages. Two periods including 34 days after planting (DAP) and 46 DAP, which represent the period prior to and after sugar accumulation, respectively, were selected for metabolomic and transcriptomic profiling. Differentially accumulated metabolites (DAMs) were mainly enriched in the pentose phosphate pathway, galactose metabolism, glycolysis/gluconeogenesis, starch and sucrose metabolism, and fructose and mannose metabolism. By orthogonal projection to latent structures-discriminant s-plot (OPLS-DA S-plot) and MetaboAnalyst analyses, D-galactose and β-D-glucose were identified as the major components of sugar accumulation in wucai. Combined with the transcriptome, the pathway of sugar accumulation and the interact network between 26 DEGs and the two sugars were mapped. CWINV4, CEL1, BGLU16, and BraA03g023380.3C had positive correlations with the accumulation of sugar accumulation in wucai. The lower expression of BraA06g003260.3C, BraA08g002960.3C, BraA05g019040.3C, and BraA05g027230.3C promoted sugar accumulation during the ripening of wucai. These findings provide insights into the mechanisms underlying sugar accumulation during commodity maturity, providing a basis for the breeding of sugar-rich wucai cultivars.

Light Drives and Temperature Modulates: Variation of Phenolic Compounds Profile in Relation to Photosynthesis in Spring Barley

Accumulation and metabolic profile of phenolic compounds (PheCs; serving as UV-screening pigments and antioxidants) as well as carbon fixation rate (A_n) and plant growth are sensitive to irradiance and temperature. Since these factors are naturally co-acting in the environment, it is worthy to study the combined effects of these environmental factors to assess their possible physiological consequences. We investigated how low and high irradiance in combination with different temperatures modify the metabolic profile of PheCs and expression of genes involved in the antioxidative enzyme and PheCs biosynthesis, in relation to photosynthetic activity and availability of non-structural carbohydrates (NSC) in spring barley seedlings. High irradiance positively affected A_n, NSC, PheCs content, and antioxidant activity (AOX). High temperature led to decreased A_n, NSC, and increased dark respiration, whilst low temperature was accompanied by reduction of UV-A shielding but increase of PheCs content and AOX. Besides that, irradiance and temperature caused changes in the metabolic profile of PheCs, particularly alteration in homoorientin/isovitexin derivatives ratio, possibly related to demands on AOX-based protection. Moreover, we also observed changes in the ratio of sinapoyl-/feruloyl- acylated flavonoids, the function of which is not yet known. The data also strongly suggested that the NSC content may support the PheCs production.

Identification of CaAN3 as a fruit-specific regulator of anthocyanin biosynthesis in pepper (Capsicum annuum)

The novel gene CaAN3 encodes an R2R3 MYB transcription factor that regulates fruit-specific anthocyanin accumulation. The key regulatory gene CaAN2 encodes an R2R3 MYB transcription factor that regulates anthocyanin biosynthesis in various tissues in pepper (Capsicum annuum). However, CaAN2 is not expressed in certain pepper accessions showing fruit-specific anthocyanin accumulation. In this study, we identified the novel locus CaAN3 as a regulator of fruit-specific anthocyanin biosynthesis, using an F₂ population derived from a hybrid cultivar with purple immature fruits and segregating for CaAN3. We extracted total RNA, assembled two RNA pools according to fruit color, and carried out bulked segregant RNA sequencing. We aligned the raw reads to the pepper reference genome Dempsey and identified 6,672 significant single nucleotide polymorphisms (SNPs) by calculating the Δ(SNP-index) between the two pools. We then conducted molecular mapping to delimit the target region of CaAN3 to the interval 184.6-186.4 Mbp on chromosome 10. We focused on Dem.v1.00043895, encoding an R2R3 MYB transcription factor, as the strongest candidate gene. Sequence analysis revealed four insertion/deletion polymorphisms in the promoter region of the green CaAN3 allele. We employed virus-induced gene silencing and transient overexpression assays to characterize the function of the candidate gene. When Dem.v1.00043895 was silenced in pepper, anthocyanin accumulation decreased in the pericarp, while the transient overexpression of Dem.v1.00043895 in Nicotiana benthamiana leaves resulted in the accumulation of anthocyanins around the infiltration sites. These results showed that Dem.v1.00043895 is CaAN3, an activator of anthocyanin biosynthesis in pepper fruits.

Glucose Supply Induces PsMYB2-Mediated Anthocyanin Accumulation in Paeonia suffruticosa 'Tai Yang' Cut Flower

Tree peony (Paeonia suffruticosa) is a well-known Chinese ornamental plant with showy flower color. However, the color fading problem during vase time seriously blocks its development in the cut flower market. In this study, we found that exogenous glucose supply improved the color quality of P. suffruticosa 'Tai Yang' cut flowers with increased total soluble sugar and anthocyanin contents of petals. Besides, the promotion effect of glucose was better than the osmotic control of 3-O-methylglucose (3OMG) treatment and the glucose analog mannose treatment. The structural genes, including PsF3H, PsF3'H, PsDFR, PsAOMT, and PsUF5GT, were remarkably upregulated under glucose treatment. Meanwhile, the regulatory genes, including PsbHLH1, PsbHLH3, PsMYB2, PsWD40-1, and PsWD40-2, also showed a strong response to glucose treatment. Among these five regulatory genes, PsMYB2 showed less response to 3OMG treatment but was highly expressed under glucose and mannose treatments, indicating that PsMYB2 may have an important role in the glucose signal pathway. Ectopic overexpression of PsMYB2 in Nicotiana tabacum resulted in a strong pigmentation in petals and stamens of tobacco flowers accompanied with multiple anthocyanin biosynthetic genes upregulated. More importantly, the overexpression of PsMYB2 enhanced the ability of glucose-induced anthocyanin accumulation in Arabidopsis thaliana seedlings since PsMYB2-overexpressing Arabidopsis showed higher expression levels of AtPAL1, AtCHS, AtF3H, AtF3'H, AtDFR, and AtLDOX than those of wild type under glucose treatment. In summary, we suggested that glucose supply promoted petal coloration of P. suffruticosa 'Tai Yang' cut flower through the signal pathway, and PsMYB2 was a key component in this process. Our research made a further understanding of the mechanism that glucose-induced anthocyanin biosynthesis of P. suffruticosa cut flowers during postharvest development, laying a foundation for color retention technology development of cut flowers.

Metabolic Profiling of White and Green Radish Cultivars (Raphanus sativus)

Radish (Raphanus sativus) is a Brassica vegetable important for human nutrition and health because it is rich in diverse metabolites. Although previous studies have evaluated various metabolites, few studies have comprehensively profiled the primary and secondary metabolites in the roots of white- and green-colored radishes. Thus, this study aimed to provide information about the contents of metabolites beneficial for human health in both cultivars and to investigate the relationships between the various metabolites detected. In particular, among the 55 metabolites detected in radish roots, the levels of most amino acids and phenolic acids, vital to nutrition and health, were higher in green radish roots, while slightly higher levels of glucosinolates were observed in white radish roots—information which can be used to develop an effective strategy to promote vegetable consumption. Furthermore, glutamic acid, as a metabolic precursor of amino acids and chlorophylls, was positively correlated with other amino acids (cysteine, tryptophan, asparagine, alanine, serine, phenylalanine, valine, isoleucine, proline, leucine, beta-alanine, lysine, and GABA), and chlorophylls (chlorophyll a and chlorophyll b) detected in radish roots and phenylalanine, a metabolic precursor of phenolic compounds, were positively correlated with kaempferol, 4-hydroxybenzoate, and catechin. In addition, strong positive correlations between carbohydrates (sucrose and glucose) and phenolics were observed in this study, indicating that sucrose and glucose function as energy sources for phenolic compounds.

Sugar signal mediates flavonoid biosynthesis in tea leaves

Sugar metabolism and flavonoid biosynthesis vary with the development of tea leaves. In order to understand the regulatory mechanisms underlying the associations between them, a comprehensive transcriptomic analysis of naturally growing tea leaves at different stages of maturity was carried out. Based on weighted gene coexpression network analysis, the key gene modules (Modules 2 and 3) related to the varying relationship between sugar metabolism and flavonoid biosynthesis as well as the corresponding hub genes were obtained. KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis showed that the transcription factors (TFs) in Modules 2 and 3 were mainly enriched in the pathway of plant hormone signal transduction. An in vitro study showed that the transcriptional levels of ERF1B-like TF for hexokinase inhibitor and sucrose treatments were upregulated, being respectively 28.1- and 30.2-fold higher than in the control, suggesting that ERF1B-like TFs participate in the sugar-induced regulation of flavonoid biosynthesis. The results of yeast one-hybrid and dual-luciferase assays demonstrated that CsF3'H, encoding flavonoid 3'-hydroxylase, was the target flavonoid biosynthetic gene for CsERF1B-like TF. Our study identified the potential key regulators participating in the metabolism of sugars and flavonoids, providing new insights into the crosstalk between sugar metabolism and flavonoid biosynthesis in tea plants.

Sucrose Enhances Anthocyanin Accumulation in Torenia by Promoting Expression of Anthocyanin Biosynthesis Genes

We examined the effects of different sucrose concentrations (3%, 5%, and 7%) on anthocyanin accumulation and plant growth in wild type (WT) and transgenic (T2) torenia cultivar “Kauai Rose” overexpressing the anthocyanin regulatory transcription factors B-Peru + mPAP1 or RsMYB1. Sucrose increased anthocyanin production in both WT and transgenic plants, with higher anthocyanin production in transgenic plants compared to WT plants. Higher sucrose concentrations increased production of anthocyanin in transgenic and WT plants, with increased anthocyanin production associated with increased expression of anthocyanin biosynthesis genes. Higher sucrose concentrations reduced growth of WT and transgenic plants. Our results indicate that sucrose enhances anthocyanin production in torenia by regulating anthocyanin biosynthesis genes.

Imperative role of sugar signaling and transport during drought stress responses in plants

Cellular sugar status is essentially maintained during normal growth conditions but is impacted negatively during various environmental perturbations. Drought presents one such unfavorable environmental cue that hampers the photosynthetic fixation of carbon into sugars and affects their transport by lowering the cellular osmotic potential. The transport of cellular sugar is facilitated by a specific set of proteins known as sugar transporters. These transporter proteins are the key determinant of influx/ efflux of various sugars and their metabolite intermediates that support the plant growth and developmental process. Abiotic stress and especially drought stress-mediated injury results in reprogramming of sugar distribution across the cellular and subcellular compartments. Here, we have reviewed the imperative role of sugar accumulation, signaling, and transport under typical and atypical stressful environments. We have discussed the physiological effects of drought on sugar accumulation and transport through different transporter proteins involved in monosaccharide and disaccharide sugar transport. Further, we have illustrated sugar-mediated signaling and regulation of sugar transporter proteins along with the overall crosstalk of this signaling with the phytohormone module of abiotic stress response under osmotic stress. Overall, the present review highlights the critical role of sugar transport, distribution and signaling in plants under drought stress conditions.

Host-produced ethylene is required for marked cell expansion and endoreduplication in dodder search hyphae

The genus Cuscuta comprises stem holoparasitic plant species with wide geographic distribution. Cuscuta spp. obtain water, nutrients, proteins, and mRNA from their host plants via a parasitic organ called the haustorium. As the haustorium penetrates into the host tissue, search hyphae elongate within the host tissue and finally connect with the host's vascular system. Invasion by Cuscuta spp. evokes various reactions within the host plant's tissues. Here, we show that, when Arabidopsis (Arabidopsis thaliana) is invaded by Cuscuta campestris, ethylene biosynthesis by the host plant promotes elongation of the parasite's search hyphae. The expression of genes encoding 1-aminocylclopropane-1-carboxylic acid (ACC) synthases, ACC SYNTHASE2 (AtACS2) and ACC SYNTHASE6 (AtACS6), was activated in the stem of Arabidopsis plants upon invasion by C. campestris. When the ethylene-deficient Arabidopsis acs octuple mutant was invaded by C. campestris, cell elongation and endoreduplication of the search hyphae were significantly reduced, and the inhibition of search hyphae growth was complemented by exogenous application of ACC. In contrast, in the C. campestris-infected Arabidopsis ethylene-insensitive mutant etr1-3, no growth inhibition of search hyphae was observed, indicating that ETHYLENE RESPONSE1-mediated ethylene signaling in the host plant is not essential for parasitism by C. campestris. Overall, our results suggest that C. campestris recognizes host-produced ethylene as a stimulatory signal for successful invasion.

The Role of Saccharides in the Mechanisms of Pathogenicity of Fusarium oxysporum f. sp. lupini in Yellow Lupine (Lupinus luteus L.)

The primary aim of this study was to determine the relationship between soluble sugar levels (sucrose, glucose, or fructose) in yellow lupine embryo axes and the pathogenicity of the hemibiotrophic fungus Fusarium oxysporum f. sp. Schlecht lupini. The first step of this study was to determine the effect of exogenous saccharides on the growth and sporulation of F. oxysporum. The second one focused on estimating the levels of ergosterol as a fungal growth indicator in infected embryo axes cultured in vitro on sugar containing-medium or without it. The third aim of this study was to record the levels of the mycotoxin moniliformin as the most characteristic secondary metabolite of F. oxysporum in the infected embryo axes with the high sugar medium and without it. Additionally, morphometric measurements, i.e., the length and fresh weight of embryo axes, were done. The levels of ergosterol were the highest in infected embryo axes with a sugar deficit. At the same time, significant accumulation of the mycotoxin moniliformin was recorded in those tissues. Furthermore, it was found that the presence of sugars in water agar medium inhibited the sporulation of the pathogenic fungus F. oxysporum in relation to the control (sporulation of the pathogen on medium without sugar), the strongest inhibiting effect was observed in the case of glucose. Infection caused by F. oxysporum significantly limited the growth of embryo axes, but this effect was more visible on infected axes cultured under sugar deficiency than on the ones cultured with soluble sugars. The obtained results thus showed that high sugar levels may lead to reduced production of mycotoxins by F. oxysporum, limiting infection development and fusariosis.

Fine mapping of the Ca3GT gene controlling anthocyanin biosynthesis in mature unripe fruit of Capsicum annuum L

The anthocyanin biosynthesis gene Ca3GT was fine-mapped in a 110.5-kb region through a map-based cloning strategy. Gene expression and promoter analyses confirmed the strong candidate gene Capana10g001978. Pepper (Capsicum annum L.) fruit can be dark green, green, light green, purple, yellow, or ivory at the juvenile stage. Anthocyanins are responsible for fruit color formation in mature unripe pepper fruit, and transient accumulation of anthocyanins is the main problem in breeding pepper plants with mature purple fruit. Only a few genes controlling this trait have been cloned. The present study aimed to map and identify an anthocyanin biosynthesis gene from pepper using an F₂ population derived from a cross between line '17C3808' (purple mature unripe fruit) and line '17C3807' (green mature unripe fruit). The trait was mapped on a 110.5-kb interval between markers SSR18213 and SSR18228 on chromosome 10. There were three open reading frames in this region; Capana10g001978 was predicted in this region as markers CAPS-78-708 and InDel146 co-segregated with it. Capana10g001978 is a structural gene encoding the GTB transcription factor involved in the biosynthesis of anthocyanins. Comparing parental sequences, two base mutations were identified in the exon of Capana10g001978, at positions + 528 bp and + 708 bp, which resulted in changes in the 176th and 236th amino acid residues, from glutamine (CAA) to histidine (CAC), causing a nonsense mutation (from CAG to CAA). Additionally, Capana10g001978 was highly expressed in the pericarp of mature, unripe pepper fruit. There were four single nucleotide polymorphisms, three sequence deletions, and one sequence insertion in the promoter region of purple, mature, and unripe pepper fruit, leading to the formation of a W-box and a GT1-motif. Thus, Capana10g001978 is a strong candidate gene of Ca3GT involved in anthocyanin biosynthesis in mature unripe pepper fruit. These results provide important information regarding the isolation and characterization of Ca3GT, and they are the starting point for studying the regulatory pathway responsible for anthocyanin biosynthesis in pepper.

Xyloglucan Is Not Essential for the Formation and Integrity of the Cellulose Network in the Primary Cell Wall Regenerated from Arabidopsis Protoplasts

The notion that xyloglucans (XG) play a pivotal role in tethering cellulose microfibrils in the primary cell wall of plants can be traced back to the first molecular model of the cell wall proposed in 1973, which was reinforced in the 1990s by the identification of Xyloglucan Endotransglucosylase/Hydrolase (XTH) enzymes that cleave and reconnect xyloglucan crosslinks in the cell wall. However, this tethered network model has been seriously challenged since 2008 by the identification of the Arabidopsis thaliana xyloglucan-deficient mutant (xxt1 xxt2), which exhibits functional cell walls. Thus, the molecular mechanism underlying the physical integration of cellulose microfibrils into the cell wall remains controversial. To resolve this dilemma, we investigated the cell wall regeneration process using mesophyll protoplasts derived from xxt1 xxt2 mutant leaves. Imaging analysis revealed only a slight difference in the structure of cellulose microfibril network between xxt1 xxt2 and wild-type (WT) protoplasts. Additionally, exogenous xyloglucan application did not alter the cellulose deposition patterns or mechanical stability of xxt1 xxt2 mutant protoplasts. These results indicate that xyloglucan is not essential for the initial assembly of the cellulose network, and the cellulose network formed in the absence of xyloglucan provides sufficient tensile strength to the primary cell wall regenerated from protoplasts.

Metabolomic analyses of the bio-corona formed on TiO2 nanoparticles incubated with plant leaf tissues

BACKGROUND

The surface of a nanoparticle adsorbs molecules from its surroundings with a specific affinity determined by the chemical and physical properties of the nanomaterial. When a nanoparticle is exposed to a biological system, the adsorbed molecules form a dynamic and specific surface layer called a bio-corona. The present study aimed to identify the metabolites that form the bio-corona around anatase TiO₂ nanoparticles incubated with leaves of the model plant Arabidopsis thaliana.

RESULTS

We used an untargeted metabolomics approach and compared the metabolites isolated from wild-type plants with plants deficient in a class of polyphenolic compounds called flavonoids.

CONCLUSIONS

These analyses showed that TiO₂ nanoparticle coronas are enriched for flavonoids and lipids and that these metabolite classes compete with each other for binding the nanoparticle surface.

Interspecific Signaling Between the Parasitic Plant and the Host Plants Regulate Xylem Vessel Cell Differentiation in Haustoria of Cuscuta campestris

The genus Cuscuta is stem parasitic angiosperms that parasitize a wide range of vascular plants via de novo formation of a distinctive parasitic organ called a haustorium. In the developing haustorium, meristematic cells, which are initiated from the stem cortical tissue, differentiate into haustorial parenchyma cells, which elongate, penetrate into the host tissues, and finally connect with the host vasculature. This interspecific vasculature connection allows the parasite to uptake water and nutrients from the host plant. Although histological aspects of haustorium development have been studied extensively, the molecular mechanisms underlying vasculature development and the interspecific connection with the host vasculature remain largely unknown. To gain insights into the interspecific cell-to-cell interactions involved in haustorium development, we established an in vitro haustorium induction system for Cuscuta campestris using Arabidopsis thaliana rosette leaves as the host plant tissue. The in vitro induction system was used to show that interaction with host tissue was required for the differentiation of parasite haustorial cells into xylem vessel cells. To further characterize the molecular events occurring during host-dependent xylem vessel cell differentiation in C. campestris, we performed a transcriptome analysis using samples from the in vitro induction system. The results showed that orthologs of genes involved in development and proliferation of vascular stem cells were up-regulated even in the absence of host tissue, whereas orthologs of genes required for xylem vessel cell differentiation were up-regulated only after some haustorial cells had elongated and contacted the host xylem. Consistent results were obtained by another transcriptome analysis of the haustorium development in C. campestris undergoing parasitization of an intact host plant. These findings suggest the involvement of host-derived signals in the regulation of non-autonomous xylem vessel differentiation and suggest that its connection to the host xylem during the haustorium development activates a set of key genes for differentiation into xylem vessel cells.

Multiple steps of leaf thickening during sun-leaf formation in Arabidopsis

Plant morphological and physiological traits exhibit plasticity in response to light intensity. Leaf thickness is enhanced under high light (HL) conditions compared with low light (LL) conditions through increases in both cell number and size in the dorsoventral direction; however, the regulation of such phenotypic plasticity in leaf thickness (namely, sun- or shade-leaf formation) during the developmental process remains largely unclear. By modifying observation techniques for tiny leaf primordia in Arabidopsis thaliana, we analysed sun- and shade-leaf development in a time-course manner and found that the process of leaf thickening can be divided into early and late phases. In the early phase, anisotropic cell elongation and periclinal cell division on the adaxial side of mesophyll tissue occurred under the HL conditions used, which resulted in the dorsoventral growth of sun leaves. Anisotropic cell elongation in the palisade tissue is triggered by blue-light irradiation. We discovered that anisotropic cell elongation processes before or after periclinal cell division were differentially regulated independent of or dependent upon signalling through blue-light receptors. In contrast, during the late phase, isotropic cell expansion associated with the endocycle, which determined the final leaf thickness, occurred irrespective of the light conditions. Sucrose production was high under HL conditions, and we found that sucrose promoted isotropic cell expansion and the endocycle even under LL conditions. Our analyses based on this method of time-course observation addressed the developmental framework of sun- and shade-leaf formation.

Transcriptome and Proteome Profiling of Different Colored Rice Reveals Physiological Dynamics Involved in the Flavonoid Pathway

Black and red rice are rich in both anthocyanin and proanthocyanin content, which belong to a large class of flavonoids derived from a group of phenolic secondary metabolites. However, the molecular pathways and mechanisms underlying the flavonoid biosynthetic pathway are far from clear. Therefore, this study was undertaken to gain insight into physiological factors that are involved in the flavonoid biosynthetic pathway in rice cultivars with red, black, and white colors. RNA sequencing of caryopsis and isobaric tags for relative and absolute quantification (iTRAQ) analyses have generated a nearly complete catalog of mRNA and expressed proteins in different colored rice cultivars. A total of 31,700 genes were identified, of which 3417, 329, and 227 genes were found specific for red, white, and black rice, respectively. A total of 13,996 unique peptides corresponding to 3916 proteins were detected in the proteomes of black, white, and red rice. Coexpression network analyses of differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) among the different rice cultivars showed significant differences in photosynthesis and flavonoid biosynthesis pathways. Based on a differential enrichment analysis, 32 genes involved in the flavonoid biosynthesis pathway were detected, out of which only CHI, F3H, ANS, and FLS were detected by iTRAQ. Taken together, the results point to differences in flavonoid biosynthesis pathways among different colored rice cultivars, which may reflect differences in physiological functions. The differences in contents and types of flavonoids among the different colored rice cultivars are related to changes in base sequences of Os06G0162500, Os09G0455500, Os09G0455500, and Os10G0536400. Current findings expand and deepen our understanding of flavonoid biosynthesis and concurrently provides potential candidate genes for improving the nutritional qualities of rice.

Transient induction of a subset of ethylene biosynthesis genes is potentially involved in regulation of grapevine bud dormancy release

Transient increases in ethylene biosynthesis, achieved by tight regulation of transcription of specific ACC oxidase and ACC synthase genes, play a role in activation of grapevine bud dormancy release. The molecular mechanisms regulating dormancy release in grapevine buds are as yet unclear. It has been hypothesized that its core involves perturbation of respiration which induces an interplay between ethylene and ABA metabolism that removes repression and allows regrowth. Roles for hypoxia and ABA metabolism in this process have been previously supported. The potential involvement of ethylene biosynthesis in regulation of dormancy release, which has received little attention so far, is now explored. Our results indicate that (1) ethylene biosynthesis is induced by hydrogen cyanamide (HC) and azide (AZ), known artificial stimuli of dormancy release, (2) inhibitors of ethylene biosynthesis and signalling antagonize dormancy release by HC/AZ treatments, (3) ethylene application induces dormancy release, (4) there are two sets of bud-expressed ethylene biosynthesis genes which are differentially regulated, (5) only one set is transiently upregulated by HC/AZ and during the natural dormancy cycle, concomitant with changes in ethylene levels, and (6) levels of ACC oxidase transcripts and ethylene sharply decrease during natural dormancy release, whereas ACC accumulates. Given these results, we propose that transient increases in ethylene biosynthesis prior to dormancy release, achieved primarily by regulation of transcription of specific ACC oxidase genes, play a role in activation of dormancy release.

Mitogen-activated protein kinase kinase 6 negatively regulates anthocyanin induction in Arabidopsis

Arabidopsis mitogen-activated protein (MAP) kinase kinase 6 (MKK6) has previously been shown to play important roles in plant immunity and cytokinesis. Here we report that it is also involved in the negative regulation of anthocyanin biosynthesis in Arabidopsis. Elevated anthocyanin levels are observed in mkk6 knock out mutant plants. RNA-sequencing analysis revealed that the expression level of MYB75 (Myb transcription factor 75), which encodes a key positive regulator of anthocyanin biosynthesis, is up-regulated in mkk6 mutant plants, suggesting that increased MYB75 expression contributes to the elevated anthocyanin levels. In addition, suppression of high sucrose-induced anthocyanin production by pathogen associated molecular pattern-triggered immunity is also dependent on MKK6, further supporting that MKK6 is a key negative regulator of anthocyanin biosynthesis in Arabidopsis.

AtMyb56 Regulates Anthocyanin Levels via the Modulation of AtGPT2 Expression in Response to Sucrose in Arabidopsis

Sucrose is a crucial compound for the growth and development of plants, and the regulation of multiple genes depends on the amount of soluble sugars present. Sucrose acts as a signaling molecule that regulates a proton-sucrose symporter, with its sensor being the sucrose transporter. Flavonoid and anthocyanin biosynthesis are regulated by sucrose, and sucrose signaling can affect flavonoid and anthocyanin accumulation. In the present study, we found a Myb transcription factor affecting accumulation of anthocyanin. AtMyb56 showed an increase in its expression in response to sucrose treatment. Under normal conditions, anthocyanin accumulation was similar between Col-0 (wild type) and atmyb56 mutant seedlings; however, under sucrose treatment, the level of anthocyanin accumulation was lower in the atmyb56 mutant plants than in Col-0 plants. Preliminary microarray analysis led to the investigation of the expression of one candidate gene, AtGPT2, in the atmyb56 mutant. The phosphate translocator, which is a plastidial phosphate antiporter family, catalyzes the import of glucose-6-phosphate (G-6-P) into the chloroplast. AtGPT2 gene expression was altered in atmyb56 seedlings in a sucrose-dependent manner in response to circadian cycle. Furthermore, the lack of AtMyb56 resulted in altered accumulation of maltose in a sucrose-dependent manner. Therefore, the sucrose responsive AtMyb56 regulates AtGPT2 gene expression in a sucrose-dependent manner to modulate maltose and anthocyanin accumulations in response to the circadian cycle.

Characterization of phenolic composition in Carignan noir grapes (Vitis vinifera L.) from six wine-growing sites in Maule Valley, Chile

BACKGROUND

Among Chilean varieties, Carignan noir has had a major resurgence due to its rediscovered wine quality potential. For this, the aim of this study was to characterize phenolic composition of grapes grown in six sites from the Maule Valley.

RESULTS

The data showed that myricetin-3-glc and catechin were the most important flavonol and flavanol, respectively. Anthocyanin and flavonol composition was correlated with biologically effective degree days, exhibiting a relationship with grape maturity. Flavanol and hydroxycinnamic acid composition was inversely correlated to the average maximum temperature of the warmest month, showing that their synthesis is favored by cooler temperatures during the warmest month.

CONCLUSION

These results have enological and viticultural interest for grape growers as vineyard site selection for this cultivar can confer differentiable attributes in terms of grape composition and quality. On the other hand, understanding the effects of climate on the synthesis of phenolic compounds may be useful for managing the vineyards with the aim of improving grape quality. © 2017 Society of Chemical Industry.

Quantitative confocal imaging method for analyzing cellulose dynamics during cell wall regeneration in Arabidopsis mesophyll protoplasts

The network structure of cellulose fibrils provides mechanical properties to the primary cell wall, thereby determining the shapes and growth patterns of plant cells. Despite intensive studies, the construction process of the network structure in muro remains largely unknown, mainly due to the lack of a robust, straightforward technique to evaluate network configuration. Here, we developed a quantitative confocal imaging method for general use in the study of cell wall dynamics in protoplasts derived from Arabidopsis leaf mesophyll cells. Confocal imaging of regenerating cell walls in protoplasts stained with Calcofluor allowed us to visualize the cellulose network, comprising strings of bundled cellulosic fibrils. Using image analysis techniques, we measured several metrics including total length, which is a measure of the spread of the cellulose network. The total length increased during cell wall regeneration. In a proof-of-concept experiment using microtubule-modifying agents, oryzalin, an inhibitor of microtubule polymerization, inhibited the increase in total length and caused abnormal orientation of the network, as shown by the decrease in the average angle of the cellulose with respect to the cell long axis. Taxol, a microtubule stabilizer, stimulated the bundling of cellulose fibrils, as shown by the increase in skewness in the fluorescence intensity distribution of Calcofluor, and inhibited the increase in total length. These results demonstrate the validity of this method for quantitative imaging of the cellulose network, providing an opportunity to gain insight into the dynamic aspects of cell wall regeneration.

Crosstalk between Photoreceptor and Sugar Signaling Modulates Floral Signal Transduction

Over the past decade, integrated genetic, cellular, proteomic and genomic approaches have begun to unravel the surprisingly crosstalk between photoreceptors and sugar signaling in regulation of floral signal transduction. Although a number of physiological factors in the pathway have been identified, the molecular genetic interactions of some components are less well understood. The further elucidation of the crosstalk mechanisms between photoreceptors and sugar signaling will certainly contribute to our better understanding of the developmental circuitry that controls floral signal transduction. This article summarizes our current knowledge of this crosstalk, which has not received much attention, and suggests possible directions for future research.

Transcriptomic Analysis of Responses to Imbalanced Carbon: Nitrogen Availabilities in Rice Seedlings

The internal C:N balance must be tightly controlled for the normal growth and development of plants. However, the underlying mechanisms, by which plants sense and balance the intracellular C:N status correspondingly to exogenous C:N availabilities remain elusive. In this study, we use comparative gene expression analysis to identify genes that are responsive to imbalanced C:N treatments in the aerial parts of rice seedlings. Transcripts of rice seedlings treated with four C:N availabilities (1:1, 1:60, 60:1 and 60:60) were compared and two groups of genes were classified: high C:low N responsive genes and low C:high N responsive genes. Our analysis identified several functional correlated genes including chalcone synthase (CHS), chlorophyll a-b binding protein (CAB) and other genes that are implicated in C:N balancing mechanism, such as alternative oxidase 1B (OsAOX1B), malate dehydrogenase (OsMDH) and lysine and histidine specific transporter 1 (OsLHT1). Additionally, six jasmonate synthetic genes and key regulatory genes involved in abiotic and biotic stresses, such as OsMYB4, autoinhibited calcium ATPase 3 (OsACA3) and pleiotropic drug resistance 9 (OsPDR9), were differentially expressed under high C:low N treatment. Gene ontology analysis showed that high C:low N up-regulated genes were primarily enriched in fatty acid biosynthesis and defense responses. Coexpression network analysis of these genes identified eight jasmonate ZIM domain protein (OsJAZ) genes and several defense response related regulators, suggesting that high C:low N status may act as a stress condition, which induces defense responses mediated by jasmonate signaling pathway. Our transcriptome analysis shed new light on the C:N balancing mechanisms and revealed several important regulators of C:N status in rice seedlings.

Sucrose-induced anthocyanin accumulation in vegetative tissue of Petunia plants requires anthocyanin regulatory transcription factors

The effects of three different sucrose concentrations on plant growth and anthocyanin accumulation were examined in non-transgenic (NT) and transgenic (T₂) specimens of the Petunia hybrida cultivar 'Mirage rose' that carried the anthocyanin regulatory transcription factors B-Peru+mPAP1 or RsMYB1. Anthocyanin accumulation was not observed in NT plants in any treatments, whereas a range of anthocyanin accumulation was observed in transgenic plants. The anthocyanin content detected in transgenic plants expressing the anthocyanin regulatory transcription factors (B-Peru+mPAP1 or RsMYB1) was higher than that in NT plants. In addition, increasing sucrose concentration strongly enhanced anthocyanin content as shown by quantitative real-time polymerase chain reaction (qRT-PCR) analysis, wherein increased concentrations of sucrose enhanced transcript levels of the transcription factors that are responsible for the induction of biosynthetic genes involved in anthocyanin synthesis; this pattern was not observed in NT plants. In addition, sucrose affected plant growth, although the effects were different between NT and transgenic plants. Taken together, the application of sucrose could enhance anthocyanin production in vegetative tissue of transgenic Petunia carrying anthocyanin regulatory transcription factors, and this study provides insights about interactive effects of sucrose and transcription factors in anthocyanin biosynthesis in the transgenic plant.

iTRAQ-Based Quantitative Proteomics Analysis of Black Rice Grain Development Reveals Metabolic Pathways Associated with Anthocyanin Biosynthesis

BACKGROUND

Black rice (Oryza sativa L.), whose pericarp is rich in anthocyanins (ACNs), is considered as a healthier alternative to white rice. Molecular species of ACNs in black rice have been well documented in previous studies; however, information about the metabolic mechanisms underlying ACN biosynthesis during black rice grain development is unclear.

RESULTS

The aim of the present study was to determine changes in the metabolic pathways that are involved in the dynamic grain proteome during the development of black rice indica cultivar, (Oryza sativa L. indica var. SSP). Isobaric tags for relative and absolute quantification (iTRAQ) MS/MS were employed to identify statistically significant alterations in the grain proteome. Approximately 928 proteins were detected, of which 230 were differentially expressed throughout 5 successive developmental stages, starting from 3 to 20 days after flowering (DAF). The greatest number of differentially expressed proteins was observed on 7 and 10 DAF, including 76 proteins that were upregulated and 39 that were downregulated. The biological process analysis of gene ontology revealed that the 230 differentially expressed proteins could be sorted into 14 functional groups. Proteins in the largest group were related to metabolic process, which could be integrated into multiple biochemical pathways. Specifically, proteins with a role in ACN biosynthesis, sugar synthesis, and the regulation of gene expression were upregulated, particularly from the onset of black rice grain development and during development. In contrast, the expression of proteins related to signal transduction, redox homeostasis, photosynthesis and N-metabolism decreased during grain maturation. Finally, 8 representative genes encoding different metabolic proteins were verified via quantitative real-time polymerase chain reaction (qRT-PCR) analysis, these genes had differed in transcriptional and translational expression during grain development.

CONCLUSIONS

Expression analyses of metabolism-related protein groups belonging to different functional categories and subcategories indicated that significantly upregulated proteins were related to flavonoid and starch synthesis. On the other hand, the downregulated proteins were determined to be related to nitrogen metabolism, as well as other functional categories and subcategories, including photosynthesis, redox homeostasis, tocopherol biosynthetic, and signal transduction. The results provide valuable new insights into the characterization and understanding of ACN pigment production in black rice.

Intronic Sequence Regulates Sugar-Dependent Expression of Arabidopsis thaliana Production of Anthocyanin Pigment-1/MYB75

Sucrose-specific regulation of gene expression is recognized as an important signaling response, distinct from glucose, which serves to modulate plant growth, metabolism, and physiology. The Arabidopsis MYB transcription factor Production of Anthocyanin Pigment-1 (PAP1) plays a key role in anthocyanin biosynthesis and expression of PAP1 is known to be regulated by sucrose. Sucrose treatment of Arabidopsis seedlings led to a 20-fold induction of PAP1 transcript, which represented a 6-fold increase over levels in glucose-treated seedlings. The PAP1 promoter was not sufficient for conferring a sucrose response to a reporter gene and did not correctly report expression of PAP1 in plants. Although we identified 3 putative sucrose response elements in the PAP1 gene, none were found to be necessary for this response. Using deletion analysis, we identified a 90 bp sequence within intron 1 of PAP1 that is necessary for the sucrose response. This sequence was sufficient for conferring a sucrose response to a minimal promoter: luciferase reporter when present in multiple copies upstream of the promoter. This work lays the foundation for dissecting the sucrose signaling pathway of PAP1 and contributes to understanding the interplay between sucrose signaling, anthocyanin biosynthesis, and stress responses.

Maize-Pathogen Interactions: An Ongoing Combat from a Proteomics Perspective

Maize (Zea mays L.) is a host to numerous pathogenic species that impose serious diseases to its ear and foliage, negatively affecting the yield and the quality of the maize crop. A considerable amount of research has been carried out to elucidate mechanisms of maize-pathogen interactions with a major goal to identify defense-associated proteins. In this review, we summarize interactions of maize with its agriculturally important pathogens that were assessed at the proteome level. Employing differential analyses, such as the comparison of pathogen-resistant and susceptible maize varieties, as well as changes in maize proteomes after pathogen challenge, numerous proteins were identified as possible candidates in maize resistance. We describe findings of various research groups that used mainly mass spectrometry-based, high through-put proteomic tools to investigate maize interactions with fungal pathogens Aspergillus flavus, Fusarium spp., and Curvularia lunata, and viral agents Rice Black-streaked Dwarf Virus and Sugarcane Mosaic Virus.

Arabidopsis ROOT HAIR DEFECTIVE3 is involved in nitrogen starvation-induced anthocyanin accumulation

Anthocyanin accumulation is a common phenomenon seen in plants under environmental stress. In this study, we identified a new allele of ROOT HAIR DEFECTIVE3 (RHD3) showing an anthocyanin overaccumulation phenotype under nitrogen starvation conditions. It is known that ethylene negatively regulates light- and sucrose-induced anthocyanin biosynthesis. We hypothesized that RHD3 achieves its negative effect on anthocyanin biosynthesis via an ethylene-regulating pathway. In support of this, similar to rhd3 mutants, the Arabidopsis ethylene signaling mutants etr1, ein2, and ein3/eil1 showed an anthocyanin overaccumulation phenotype under nitrogen starvation conditions. The ethylene precursor ACC strongly suppressed anthocyanin accumulation, dependent on ETR1, EIN2, EIN3/EIL1, and, partially, RHD3. In addition, inactivating RHD3 partially reversed the suppressive effect of ETO1 inactivation-evoked endogenous ethylene production on anthocyanin accumulation. The expression of nitrogen starvation-induced anthocyanin biosynthesis genes was negatively regulated by RHD3, but ethylene response genes were positively regulated by RHD3. Wild-type seedlings overexpressing RHD3 showed similar phenotypes to rhd3 mutants, indicating the existence of a fine-tuned relationship between gene expression and function. RHD3 was initially identified as a gene involved in root hair development. This study uncovered a new physiological function of RHD3 in nitrogen starvation-induced anthocyanin accumulation and ethylene homeostasis. [Correction added on 6 August 2015, after first online publication: "RND3" corrected to "RHD3".].

Characterization of an activation-tagged mutant uncovers a role of GLABRA2 in anthocyanin biosynthesis in Arabidopsis

In Arabidopsis, anthocyanin biosynthesis is controlled by a MYB-bHLH-WD40 (MBW) transcriptional activator complex. The MBW complex activates the transcription of late biosynthesis genes in the flavonoid pathway, leading to the production of anthocyanins. A similar MBW complex regulates epidermal cell fate by activating the transcription of GLABRA2 (GL2), a homeodomain transcription factor required for trichome formation in shoots and non-hair cell formation in roots. Here we provide experimental evidence to show that GL2 also plays a role in regulating anthocyanin biosynthesis in Arabidopsis. From an activation-tagged mutagenized population of Arabidopsis plants, we isolated a dominant, gain-of-function mutant with reduced anthocyanins. Molecular cloning revealed that this phenotype is caused by an elevated expression of GL2, thus the mutant was named gl2-1D. Consistent with the view that GL2 acts as a negative regulator of anthocyanin biosynthesis, gl2-1D seedlings accumulated less whereas gl2-3 seedlings accumulated more anthocyanins in response to sucrose. Gene expression analysis indicated that expression of late, but not early, biosynthesis genes in the flavonoid pathway was dramatically reduced in gl2-1D but elevated in gl2-3 mutants. Further analysis showed that expression of some MBW component genes involved in the regulation of late biosynthesis genes was reduced in gl2-1D but elevated in gl2-3 mutants, and chromatin immunoprecipitation results indicated that some MBW component genes are targets of GL2. We also showed that GL2 functions as a transcriptional repressor. Taken together, these results indicate that GL2 negatively regulates anthocyanin biosynthesis in Arabidopsis by directly repressing the expression of some MBW component genes.

Jasmonoyl-L-isoleucine coordinates metabolic networks required for anthesis and floral attractant emission in wild tobacco (Nicotiana attenuata)

Jasmonic acid and its derivatives (jasmonates [JAs]) play central roles in floral development and maturation. The binding of jasmonoyl-L-isoleucine (JA-Ile) to the F-box of CORONATINE INSENSITIVE1 (COI1) is required for many JA-dependent physiological responses, but its role in anthesis and pollinator attraction traits remains largely unexplored. Here, we used the wild tobacco Nicotiana attenuata, which develops sympetalous flowers with complex pollination biology, to examine the coordinating function of JA homeostasis in the distinct metabolic processes that underlie flower maturation, opening, and advertisement to pollinators. From combined transcriptomic, targeted metabolic, and allometric analyses of transgenic N. attenuata plants for which signaling deficiencies were complemented with methyl jasmonate, JA-Ile, and its functional homolog, coronatine (COR), we demonstrate that (1) JA-Ile/COR-based signaling regulates corolla limb opening and a JA-negative feedback loop; (2) production of floral volatiles (night emissions of benzylacetone) and nectar requires JA-Ile/COR perception through COI1; and (3) limb expansion involves JA-Ile-induced changes in limb fresh mass and carbohydrate metabolism. These findings demonstrate a master regulatory function of the JA-Ile/COI1 duet for the main function of a sympetalous corolla, that of advertising for and rewarding pollinator services. Flower opening, by contrast, requires JA-Ile signaling-dependent changes in primary metabolism, which are not compromised in the COI1-silenced RNA interference line used in this study.

Temporal and spatial control of gene expression in horticultural crops

Biotechnology provides plant breeders an additional tool to improve various traits desired by growers and consumers of horticultural crops. It also provides genetic solutions to major problems affecting horticultural crops and can be a means for rapid improvement of a cultivar. With the availability of a number of horticultural genome sequences, it has become relatively easier to utilize these resources to identify DNA sequences for both basic and applied research. Promoters play a key role in plant gene expression and the regulation of gene expression. In recent years, rapid progress has been made on the isolation and evaluation of plant-derived promoters and their use in horticultural crops, as more and more species become amenable to genetic transformation. Our understanding of the tools and techniques of horticultural plant biotechnology has now evolved from a discovery phase to an implementation phase. The availability of a large number of promoters derived from horticultural plants opens up the field for utilization of native sequences and improving crops using precision breeding. In this review, we look at the temporal and spatial control of gene expression in horticultural crops and the usage of a variety of promoters either isolated from horticultural crops or used in horticultural crop improvement.

An update on sugar transport and signalling in grapevine

In addition to their role as a source of reduced carbon, sugars may directly or indirectly control a wide range of activities in plant cells, through transcriptional and post-translational regulation. This control has been studied in detail using Arabidopsis thaliana, where genetic analysis offers many possibilities. Much less is known about perennial woody species. For several years, various aspects of sugar sensing and signalling have been investigated in the grape (Vitis vinifera L.) berry, an organ that accumulates high concentrations of hexoses in the vacuoles of flesh cells. Here we review various aspects of this topic: the molecular basis of sugar transport and its regulation by sugars in grapevine; the functional analysis of several sugar-induced genes; the effects of some biotic and abiotic stresses on the sugar content of the berry; and finally the effects of exogenous sugar supply on the ripening process in field conditions. A picture of complex feedback and multiprocess regulation emerges from these data.

Direct isolation of flavonoids from plants using ultra-small anatase TiO₂ nanoparticles

Surface functionalization of nanoparticles has become an important tool for in vivo delivery of bioactive agents to their target sites. Here we describe the reverse strategy, nanoharvesting, in which nanoparticles are used as a tool to isolate bioactive compounds from living cells. Anatase TiO₂ nanoparticles smaller than 20 nm form strong bonds with molecules bearing enediol and especially catechol groups. We show that these nanoparticles enter plant cells, conjugate enediol and catechol group-rich flavonoids in situ, and exit plant cells as flavonoid-nanoparticle conjugates. The source plant tissues remain viable after treatment. As predicted by the surface chemistry of anatase TiO₂ nanoparticles, quercetin-based flavonoids were enriched amongst the nanoharvested flavonoid species. Nanoharvesting eliminates the use of organic solvents, allows spectral identification of the isolated compounds, and opens new avenues for use of nanomaterials for coupled isolation and testing of bioactive properties of plant-synthesized compounds.

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.

Regulatory effect of stems on sucrose-induced chlorophyll degradation and anthocyanin synthesis in Egeria densa leaves

Detached green leaves of the aquatic plant Egeria densa showed chlorophyll degradation and turned red due to induced anthocyanin synthesis incubated in 0.1 M sucrose under continuous light for 7-10 days. If the leaves were placed in water, only chlorophyll degradation occurred and the detached leaves turned yellow. The levels of endogenous total carbohydrates increased in detached leaves cultured in the sucrose solution but only increased marginally in water. If the leaves were still attached to a piece of stem, with a node on either side of the single leaf whorl, then they did not accumulate anthocyanin in culture with 0.1 M sucrose. These leaves showed a similar increase in total carbohydrates and degradation of chlorophyll as detached leaves. Attached leaves, in which the midrib had been cut in situ, showed localized accumulation of anthocyanin in the leaf tissue distal to the cut in the midrib when cultured in 0.1 M sucrose. These results suggest that the stem plays a regulatory role in anthocyanin synthesis in attached leaves cultured in a sucrose solution but does not influence chlorophyll degradation or carbohydrate accumulation.

Cross-talk interactions of exogenous nitric oxide and sucrose modulates phenylpropanoid metabolism in yellow lupine embryo axes infected with Fusarium oxysporum

The aim of the study was to examine cross-talk of exogenous nitric oxide (NO) and sucrose in the mechanisms of synthesis and accumulation of isoflavonoids in embryo axes of Lupinus luteus L. cv. Juno. It was verified whether the interaction of these molecules can modulate the defense response of axes to infection and development of the pathogenic fungus Fusarium oxysporum f. sp. lupini. Sucrose alone strongly stimulated a high level of genistein glucoside in axes pretreated with exogenous nitric oxide (SNP or GSNO) and non-pretreated axes. As a result of amplification of the signal coming from sucrose and GSNO, high isoflavonoids accumulation was observed (+Sn+GSNO). It needs to be stressed that infection in tissues pretreated with SNP/GSNO and cultured on the medium with sucrose (+Si+SNP/+Si+GSNO) very strongly enhances the accumulation of free isoflavone aglycones. In +Si+SNP axes phenylalanine ammonia-lyase activity was high up to 72h. As early as at 12h in +Si+SNP axes an increase was recorded in gene expression level of the specific isoflavonoid synthesis pathway. At 24h in +Si+SNP axes a very high total antioxidant capacity dependent on the pool of fast antioxidants was noted. Post-infection generation of semiquinone radicals was lower in axes with a high level of sucrose than with a deficit.

Mutations in HISTONE ACETYLTRANSFERASE1 affect sugar response and gene expression in Arabidopsis

Nutrient response networks are likely to have been among the first response networks to evolve, as the ability to sense and respond to the levels of available nutrients is critical for all organisms. Although several forward genetic screens have been successful in identifying components of plant sugar-response networks, many components remain to be identified. Toward this end, a reverse genetic screen was conducted in Arabidopsis thaliana to identify additional components of sugar-response networks. This screen was based on the rationale that some of the genes involved in sugar-response networks are likely to be themselves sugar regulated at the steady-state mRNA level and to encode proteins with activities commonly associated with response networks. This rationale was validated by the identification of hac1 mutants that are defective in sugar response. HAC1 encodes a histone acetyltransferase. Histone acetyltransferases increase transcription of specific genes by acetylating histones associated with those genes. Mutations in HAC1 also cause reduced fertility, a moderate degree of resistance to paclobutrazol and altered transcript levels of specific genes. Previous research has shown that hac1 mutants exhibit delayed flowering. The sugar-response and fertility defects of hac1 mutants may be partially explained by decreased expression of AtPV42a and AtPV42b, which are putative components of plant SnRK1 complexes. SnRK1 complexes have been shown to function as central regulators of plant nutrient and energy status. Involvement of a histone acetyltransferase in sugar response provides a possible mechanism whereby nutritional status could exert long-term effects on plant development and metabolism.

Comparative proteomic analysis of the plant-virus interaction in resistant and susceptible ecotypes of maize infected with sugarcane mosaic virus

Sugarcane mosaic virus (SCMV) is an important viral pathogen and has caused serious losses in grain and forage yield. To identify candidate SCMV resistance proteins and to explore the molecular mechanisms involved in the plant-SCMV interaction, we conducted proteomic analyses of leaf samples from resistant and susceptible ecotypes of maize infected with SCMV. Proteins were analyzed by quantitative two-dimensional differential gel electrophoresis (2D-DIGE), and 93 protein spots showed statistically significant differences after virus inoculation. Functional categorization showed that SCMV-responsive proteins were mainly involved in energy and metabolism, stress and defense responses, photosynthesis, and carbon fixation. The majority of the identified proteins were located in chloroplast and cytoplasm based on bioinformatic analysis. Among these identified proteins, 17 have not been identified previously as virus-responsive proteins, and 7 were new and did not have assigned functions. Western blotting analyses confirmed the expression patterns of proteins of specific interest, and the genes encoding these proteins were further analyzed by real-time PCR. The results of this study showed overlapping and specific proteomic responses to SCMV infection between resistant and susceptible maize ecotypes. This study provides further insight into the molecular events during compatible and incompatible interactions between viruses and host plants.

BIOLOGICAL SIGNIFICANCE

Sugarcane mosaic virus (SCMV) is an important viral pathogen and has caused serious losses in grain and forage yield. However, little is known about host-SCMV interactions from the proteome perspective. This study analyzed proteomic changes in resistant and susceptible plants that are infected with SCMV using DIGE based proteomics. We identified 17 proteins that have not been identified previously as virus-responsive proteins, and 7 new proteins without assigned functions. These proteins are interesting candidates for future research, as they may be associated with new biological functions and play important roles in plant-virus interactions. Real-time RT-PCR analysis of genes encoding several proteins of interest provided indication on whether the changes in protein abundance were regulated at the mRNA level. The results of this study showed overlapping and specific proteomic responses to SCMV infection between resistant and susceptible ecotypes. After inoculation, the proteins involved in energy and metabolism, stress and defense responses, photosynthesis and other four functional groups showed significant changes in both ecotypes, which suggested that SCMV infection influenced these physiological processes in both the resistant Siyi and the susceptible Mo17. However, the oxidative burst was more pronounced during incompatible plant-SCMV interactions, as compared to those defined as compatible. We also observed an increase of enzymes involved in glycolysis and gluconeogenesis pathways in the resistant maize ecotype Siyi, while decrease in the susceptible maize ecotype Mo17. In addition, there is a marked increase of guanine nucleotide-binding protein beta submit in the resistant Siyi, which suggests a possible involvement of G-protein associated pathways in the resistant responses of maize to SCMV. These observations may possibly reveal protein targets/markers that are useful in the design of future diagnosis or plant protection strategies and provide new insights into the molecular mechanism of plant-virus interactions.

Analysis of Arabidopsis glucose insensitive growth mutants reveals the involvement of the plastidial copper transporter PAA1 in glucose-induced intracellular signaling

Sugars play important roles in many aspects of plant growth and development, acting as both energy sources and signaling molecules. With the successful use of genetic approaches, the molecular components involved in sugar signaling have been identified and their regulatory roles in the pathways have been elucidated. Here, we describe novel mutants of Arabidopsis (Arabidopsis thaliana), named glucose insensitive growth (gig), identified by their insensitivity to high-glucose (Glc)-induced growth inhibition. The gig mutant displayed retarded growth under normal growth conditions and also showed alterations in the expression of Glc-responsive genes under high-Glc conditions. Our molecular identification reveals that GIG encodes the plastidial copper (Cu) transporter PAA1 (for P(1B)-type ATPase 1). Interestingly, double mutant analysis indicated that in high Glc, gig is epistatic to both hexokinase1 (hxk1) and aba insensitive4 (abi4), major regulators in sugar and retrograde signaling. Under high-Glc conditions, the addition of Cu had no effect on the recovery of gig/paa1 to the wild type, whereas exogenous Cu feeding could suppress its phenotype under normal growth conditions. The expression of GIG/PAA1 was also altered by mutations in the nuclear factors HXK1, ABI3, and ABI4 in high Glc. Furthermore, a transient expression assay revealed the interaction between ABI4 and the GIG/PAA1 promoter, suggesting that ABI4 actively regulates the transcription of GIG/PAA1, likely binding to the CCAC/ACGT core element of the GIG/PAA1 promoter. Our findings indicate that the plastidial Cu transporter PAA1, which is essential for plastid function and/or activity, plays an important role in bidirectional communication between the plastid and the nucleus in high Glc.

Demethylesterification of the primary wall by PECTIN METHYLESTERASE35 provides mechanical support to the Arabidopsis stem

Secondary cell walls, which contain lignin, have traditionally been considered essential for the mechanical strength of the shoot of land plants, whereas pectin, which is a characteristic component of the primary wall, is not considered to be involved in the mechanical support of the plant. Contradicting this conventional knowledge, loss-of-function mutant alleles of Arabidopsis thaliana PECTIN METHYLESTERASE35 (PME35), which encodes a pectin methylesterase, showed a pendant stem phenotype and an increased deformation rate of the stem, indicating that the mechanical strength of the stem was impaired by the mutation. PME35 was expressed specifically in the basal part of the inflorescence stem. Biochemical characterization showed that the activity of pectin methylesterase was significantly reduced in the basal part of the mutant stem. Immunofluorescence microscopy and immunogold electron microscopy analyses using JIM5, JIM7, and LM20 monoclonal antibodies revealed that demethylesterification of methylesterified homogalacturonans in the primary cell wall of the cortex and interfascicular fibers was suppressed in the mutant, but lignified cell walls in the interfascicular and xylary fibers were not affected. These phenotypic analyses indicate that PME35-mediated demethylesterification of the primary cell wall directly regulates the mechanical strength of the supporting tissue.

Repression of sucrose/ultraviolet B light-induced flavonoid accumulation in microbe-associated molecular pattern-triggered immunity in Arabidopsis

Recognition of microbe-associated molecular patterns (MAMPs) leads to the generation of MAMP-triggered immunity (MTI), which restricts the invasion and propagation of potentially infectious microbes. It has been described that the perception of different bacterial and fungal MAMPs causes the repression of flavonoid induction upon light stress or sucrose application. However, the functional significance of this MTI-associated signaling output remains unknown. In Arabidopsis (Arabidopsis thaliana), FLAGELLIN-SENSING2 (FLS2) and EF-TU RECEPTOR act as the pattern recognition receptors for the bacterial MAMP epitopes flg22 (of flagellin) and elf18 (of elongation factor [EF]-Tu), respectively. Here, we reveal that reactive oxygen species spiking and callose deposition are dispensable for the repression of flavonoid accumulation by both pattern recognition receptors. Importantly, FLS2-triggered activation of PATHOGENESIS-RELATED (PR) genes and bacterial basal defenses are enhanced in transparent testa4 plants that are devoid of flavonoids, providing evidence for a functional contribution of flavonoid repression to MTI. Moreover, we identify nine small molecules, of which eight are structurally unrelated, that derepress flavonoid accumulation in the presence of flg22. These compounds allowed us to dissect the FLS2 pathway. Remarkably, one of the identified compounds uncouples flavonoid repression and PR gene activation from the activation of reactive oxygen species, mitogen-activated protein kinases, and callose deposition, corroborating a close link between the former two outputs. Together, our data imply a model in which MAMP-induced repression of flavonoid accumulation serves a role in removing the inherent inhibitory action of flavonoids on an MTI signaling branch.

Evaluation of several holding solutions for prolonging vase-life and keeping quality of cut sweet pea flowers (Lathyrus odoratus L.)

Cut spikes of sweet pea (Lathyrus odoratus L.) were kept in 2% sucrose, 200 ppm 8-hydroxyquinoline sulfate (8-HQS), pulsing treatment with 200 ppm 8-HQS in combination with 2% sucrose for 12 h, pulsing the spikes with 0.2 mM silver thiosulfate (STS) for 1 h and pulsing with 0.2 mM STS for 1 h followed by 2% sucrose solution. Therefore, this study aimed to see their effects on keeping quality and vase-life of the cut flowers. A control (deionized water) and a standard preservative were also included in the experiment. The results showed that all treatments had improved the keeping quality and vase-life of the cut flowers comparing to control ones. Among all these treatments, the 8-HQS combined with 2% sucrose showed the best water uptake, water balance, percentage of maximum increase in fresh weight of the cut flower stems and vase-life which was extended up to 17 days. Moreover, this keeping solution retarded the chlorophyll as well as carbohydrate degradation. However, anthocyanin concentrations were increased by treatments with sucrose alone or STS followed by sucrose during the postharvest life. It has been concluded that 200 ppm 8-HQS combined with 2% sucrose solution has the potential to be used as a commercial cut flower preservative solution to delay flower senescence, enhance post harvest quality and prolong the vase-life of sweet pea cut flowers.

Isolation, characterization, and function analysis of a flavonol synthase gene from Ginkgo biloba

Flavonols are produced by the desaturation of dihydroflavanols, which is catalyzed by flavonol synthase (FLS). FLS belongs to the 2-oxoglutarate iron-dependent oxygenase family. The full-length cDNA and genomic DNA sequences of the FLS gene (designated as GbFLS) were isolated from Ginkgo biloba. The full-length cDNA of GbFLS contained a 1023-bp open reading frame encoding a 340-amino-acid protein. The GbFLS genomic DNA had three exons and two introns. The deduced GbFLS protein showed high identities with other plant FLSs. The conserved amino acids (H-X-D) ligating ferrous iron and residues (R-X-S) participating in 2-oxoglutarate binding were found in GbFLS at similar positions like other FLSs. GbFLS was found to be expressed in all tested tissues including roots, stems, leaves, and fruits. Expression profiling analyses revealed that GbFLS expression was induced by all of the six tested abiotic stresses, namely, UV-B, abscisic acid, cold, sucrose, salicylic acid, and ethephon, consistent with the in silico analysis results of the promoter region. The recombinant protein was successfully expressed in the E. coli strain BL21 (DE3) with a pET-28a vector. The in vitro enzyme activity assay by high performance liquid chromatography indicated that recombinant GbFLS protein could catalyze the formation of dihydrokaempferol to kaempferol and the conversion of kaempferol from naringenin, suggesting that GbFLS is a bifunctional enzyme within the flavonol biosynthetic pathway.

A mutation in the purine biosynthetic enzyme ATASE2 impacts high light signalling and acclimation responses in green and chlorotic sectors of Arabidopsis leaves

In this report, we investigate the altered APX2 expression 13 (alx13) mutation of Arabidopsis thaliana, a mutation in glutamine phosphoribosyl pyrophosphate amidotransferase 2 (ATASE2), the primary isoform of the enzyme mediating the first committed step of purine biosynthesis. Light-dependent leaf variegation was exhibited by alx13 plants, with partial shading of alx13 rosettes revealing that the development of chlorosis in emerging leaves is influenced by the growth irradiance of established leaves. Chlorotic sectors arose from emerging green alx13 leaves during a phase of rapid cell division and expansion, which shows that each new cell's fate is independent of its progenitor. In conjunction with the variegated phenotype, alx13 plants showed altered high light stress responses, including changed expression of genes encoding proteins with antioxidative functions, impaired anthocyanin production and over-accumulation of reactive oxygen species. These characteristics were observed in both photosynthetically-normal green tissues and chlorotic tissues. Chlorotic tissues of alx13 leaves accumulated mRNAs of nuclear-encoded photosynthesis genes that are repressed in other variegated mutants of Arabidopsis. Thus, defective purine biosynthesis impairs chloroplast biogenesis in a light-dependent manner and alters the induction of high light stress pathways and nuclear-encoded photosynthesis genes.

Cross-talk interactions of sucrose and Fusarium oxysporum in the phenylpropanoid pathway and the accumulation and localization of flavonoids in embryo axes of yellow lupine

This study investigated the effects of cross-talk interactions of sucrose and infection caused by a pathogenic fungus Fusarium oxysporum f.sp. lupini on the regulation of the phenylpropanoid pathway, i.e. the level of expression of genes encoding enzymes participating in flavonoid biosynthesis, as well as cell location and accumulation of these compounds in embryo axes of Lupinus luteus L. cv. Polo. Embryo axes, both non-inoculated and inoculated, were cultured for 96h on Heller medium with 60mM sucrose (+Sn and +Si) or without it (-Sn and -Si). Real-time RT-PCR to assess expression levels of the flavonoid biosynthetic genes, phenylalanine ammonialyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI) and isoflavone synthase (IFS) were used. Sucrose alone strongly stimulated the expression of these genes. There was a very high expression level of these genes in +Si embryo axes in the early phase of infection. Signal amplification by sucrose and the infection was most intense in the 48-h +Si axes, resulting in the highest level of expression of flavonoid biosynthetic genes. In -Si tissues, the expression level of these genes increased at 48 and 72h after inoculation relative to 24h; however, the relative level of expression was much lower than in +Si axes, except at 72h for PAL and CHS.Moreover, at 48h of culture, considerably higher activity of CHI (EC 5.5.1.6) was observed in axes with a high level of sucrose than in those with a sucrose deficit. CHI activity in +Si axes at 48 and 96h post-inoculation was over 1.5 and 2 times higher than that in +Sn axes, as well as higher than in -Si axes.Observations of yellow lupine embryo axes under a confocal microscope showed an increased post-infection accumulation of flavonoids, particularly in cells of embryo axes infected with F. oxysporum and cultured on a medium containing sucrose (+Si). Up to 48h post-infection in +Si axes, a very intensive emission of green fluorescence was observed, indicating high accumulation of these compounds in whole cells. Moreover, a nuclear location of flavonoids was recorded in cells. Strong staining of flavonoid end products in +Si embryo axes was consistent with the expression of PAL, CHS, CHI and IFS.These results indicate that, in the early phase of infection, the flavonoid biosynthesis pathway is considerably enhanced in yellow lupine embryo axes as a strong signal amplification effect of sucrose and the pathogenic fungus F. oxysporum.

The ethylene signaling pathway has a negative impact on sucrose-induced anthocyanin accumulation in Arabidopsis

In an attempt to understand the complex regulatory mechanisms underlying sucrose-induced flavonoid biosynthesis, we examined several Arabidopsis mutants with altered anthocyanin accumulation. We determined that disruption of ethylene signaling results in a dramatic increase in sucrose-induced anthocyanin accumulation. Furthermore, we investigated why the ein2-1 (ethylene insensitive) Arabidopsis mutant accumulates higher levels of anthocyanin in response to sucrose than wild-type Arabidopsis. An increased level of PAP1 transcript in the ein2-1 mutant appears to be the main factor responsible for the increased accumulation of anthocyanin in response to sucrose. Therefore, our results indicate that the ethylene signaling pathway plays a negative role in sucrose-induced anthocyanin accumulation. We believe that the explanation for this observation may be related to the initiation of the senescence program in plants.

Metabolic changes of Brassica rapa transformed with a bacterial isochorismate synthase gene

Metabolome analysis by 1-dimensional proton nuclear magnetic resonance (¹H NMR) coupled with multivariate data analysis was carried out in Brassica rapa plants transformed with a gene encoding bacterial isochorismate synthase (ICS). Partial least square-discrimination analysis (PLS-DA) on selected signals suggested that the resonances that were dominant in the transgenic plants corresponded to a glucosinolate (neoglucobrassicin), phenylpropanoids (sinapoyl malate, feruloyl malate, caffeoyl malate), organic acids (succinic acid and fumaric acid) and sugars (α- and β-glucose). In contrast, amino acids alanine threonine, valine, leucine were dominant in the untransformed controls. In addition, HPLC data showed that the transgenic plant accumulated salicylic acid (SA) at significantly higher levels than the control plants, whereas the phylloquinone levels were not affected. The results suggest that the expression of the bacterial isochorismate synthase gene in B. rapa does not affect fluxes into pathways to other groups of secondary metabolites through competition for the same precursor. On the contrary, the biosynthesis of isochorismate-derived products (SA) seems to induce the competitive pathways via phenylalanine (phenylpropanoids) and tryptophan (IAA and indole glucosinolates).

Tuber-specific silencing of the acid invertase gene substantially lowers the acrylamide-forming potential of potato

Some popular processed foods including French fries contain small amounts of toxic acrylamide. Efforts to lower the accumulation of this reactive compound by modifying the production process have a negative effect on sensory characteristics and are not broadly applicable. This study optimized a method developed more than a decade ago to lower the accumulation of the acrylamide precursors glucose and fructose in cold-stored tubers. In contrast to the original application, which lowered hexose content by one-third through constitutive expression of an antisense copy of the cold-inducible acid invertase (Inv) gene, the current approach was based on tuber-specific expression of an Inv-derived inverted repeat. Stored tubers of transgenic plants contained as little as 2% of the reducing sugars that accumulated in controls. This decline in glucose and fructose formation is counterbalanced by increased sucrose and starch levels. However, it did not trigger any phenotypic changes and also did not affect the formation of free asparagine, ascorbic acid, phenylalanine, and chlorogenic acid. Importantly, French fries from the low-invertase tubers contained up to 8-fold reduced amounts of acrylamide. Given the important role of processed potato products in the modern Western diet, a replacement of current varieties with the low-hexose potatoes would reduce the average daily intake of acrylamide by one-fourth.