A system in which anthocyanin synthesis is induced in regenerated torenia shoots

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.

The transcription factor AtGLK1 acts upstream of MYBL2 to genetically regulate sucrose-induced anthocyanin biosynthesis in Arabidopsis

BACKGROUND

The regulation of anthocyanin biosynthesis by various factors including sugars, light and abiotic stresses is mediated by numerous regulatory factors acting at the transcriptional level. Here experimental evidence was provided in order to demonstrate that the nuclear GARP transcription factor AtGLK1 plays an important role in regulating sucrose-induced anthocyanin biosynthesis in Arabidopsis.

RESULTS

The results obtained using real-time quantitative PCR and GUS staining assays revealed that AtGLK1 was mainly expressed in the green tissues of Arabidopsis seedlings and could be induced by sucrose. The loss-of-function glk1 glk2 double mutant has lower anthocyanin levels than the glk2 single mutant, although it has been determined that loss of AtGLK1 alone does not affect anthocyanin accumulation. Overexpression of AtGLK1 enhances the accumulation of anthocyanin in transgenic Arabidopsis seedlings accompanied by increased expression of anthocyanin biosynthetic and regulatory genes. Moreover, we found that AtGLK1 also participates in plastid-signaling mediated anthocyanin accumulations. Genetic, physiological, and molecular biological approaches demonstrated that AtGLK1 acts upstream of MYBL2, which is a key negative regulator of anthocyanin biosynthesis, to genetically regulate sucrose-induced anthocyanin biosynthesis.

CONCLUSION

Our results indicated that AtGLK1 positively regulates sucrose-induced anthocyanin biosynthesis in Arabidopsis via MYBL2.

Girled-induced anthocyanin accumulation in red-leafed Prunus cerasifera: Effect on photosynthesis, photoprotection and sugar metabolism

The feedback regulation of photosynthesis depends on the cooperation of multiple signals, including sugars. Herein, the effect of shoot girdling was monitored on a daily basis for three days in green- and red-leafed Prunus cerasifera plants (GLP and RLP, respectively). The effect of anthocyanin presence was investigated in terms of photosynthesis, sugar metabolism and photoprotection. Net photosynthesis (A₃₉₀) and stomatal conductance were reduced on the first day at 12:00 only in the girdled GLP (29 and 33 %, respectively). Moreover, the girdled GLP displayed at 12:00 higher sucrose, glucose and fructose concentrations than control leaves. Conversely, girdled RLP showed the first reduction of A₃₉₀ at 18:00, with no significant differences at 12:00 in sucrose and glucose concentrations. The increased biosynthesis of anthocyanins that was only detected in girdled RLP contributed to lowering the accumulation of hexoses. Overall, these results revealed a sugar-buffering role exerted by anthocyanins that positively influence the feedback regulation of photosynthesis. Moreover, non-photochemical quenching, namely pNPQ, revealed the ability of anthocyanins to photoprotect photosystem II from supernumerary photons reaching the chloroplast, whose function was compromised by girdling. The present study provides a starting point to understand the possible link between photosynthesis regulation through sugar signalling and anthocyanin upregulation.

Identification of anthocyanin biosynthesis related microRNAs in a distinctive Chinese radish (Raphanus sativus L.) by high-throughput sequencing

Anthocyanins are widely distributed water-soluble phytochemical pigments belonging to the flavonoid group. To date, limited knowledge is available about the regulatory roles of miRNAs in anthocyanin biosynthesis in plants. To identify the miRNAs associated with anthocyanin biosynthesis in radish, five small RNA (sRNA) libraries constructed from 'Xinlimei' radish roots at 11, 21, 44, 56 and 73 days (d) were examined using high-throughput sequencing technology. A total of 102.02 million (M) clean reads were generated, from which 483 known and 1415 novel miRNAs were identified. Combined with target prediction and annotation, 72 differentially expressed miRNAs (52 known and 20 novel miRNAs) were more likely to participate in anthocyanin biosynthesis. Several target genes for these miRNAs encode a few transcription factors, including Myb domain (MYB), basic helix-loop-helix (bHLH), WD40 repeat, squamosa promoter binding protein like (SPL), auxin response factor (ARF), ethylene insensitive 3 (EIN3), WRKY and MADS-box proteins. Furthermore, the expression patterns of some anthocyanin biosynthesis related miRNAs and their corresponding targets were validated by RT-qPCR. Based on the characterization of anthocyanin biosynthesis related miRNAs and their target genes, a putative miRNA-target module regulating anthocyanin biosynthesis was proposed. This study represents the first genome-wide identification of miRNAs associated with anthocyanin biosynthesis in radish, and provides insights into the molecular mechanisms underlying regulation of anthocyanin biosynthesis in radish and other crops.

Increased Sucrose in the Hypocotyls of Radish Sprouts Contributes to Nitrogen Deficiency-Induced Anthocyanin Accumulation

Effects of nitrogen (N) deficiency and sucrose (Suc) addition on regulation of anthocyanin biosynthesis and their relationship were investigated in this study. Radish sprouts subjected to N deficiency had 50% higher anthocyanin accumulation than when grown in Hoagland solution (a nutrient medium with all macronutrients). The contents of endogenous soluble sugars (Suc, fructose, and glucose) in the hypocotyls were also markedly increased by N limitation, with Suc showing the highest increase. Inhibition of carbohydrate biosynthesis by addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) also eliminated N deficiency-induced anthocyanin accumulation. The latter was further supported by the expression of anthocyanin biosynthesis related genes and decreased activities of nitrate reductase in the presence of Suc. Together our results indicate that N deficiency-induced anthocyanin accumulation was, at least partly, dependent on the increase of the soluble sugar, especially Suc. This work is the first comprehensive study on relationship between N deficiency and sugar content on anthocyanin accumulation in the hypocotyls of radish sprouts.

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.

Phosphorus starvation induces post-transcriptional CHS gene silencing in Petunia corolla

The corolla of Petunia 'Magic Samba' exhibits unstable anthocyanin expression depending on its phosphorus content. Phosphorus deficiency enhanced post-transcriptional gene silencing of chalcone synthase - A in the corolla. Petunia (Petunia hybrida) 'Magic Samba' has unstable red-white bicolored corollas that respond to nutrient deficiency. We grew this cultivar hydroponically using solutions that lacked one or several nutrients to identify the specific nutrient related to anthocyanin expression in corolla. The white area of the corolla widened under phosphorus (P)-deficient conditions. When the P content of the corolla grown under P-deficient conditions dropped to <2,000 ppm, completely white corollas continued to develop in >40 corollas until the plants died. Other elemental deficiencies had no clear effects on anthocyanin suppression in the corolla. After phosphate was resupplied to the P-deficient plants, anthocyanin was restored in the corollas. The expression of chalcone synthase-A (CHS-A) was suppressed in the white area that widened under P-suppressed conditions, whereas the expression of several other genes related to anthocyanin biosynthesis was enhanced more in the white area than in the red area. Reddish leaves and sepals developed under the P-deficient condition, which is a typical P-deficiency symptom. Two genes related to anthocyanin biosynthesis were enhanced in the reddish organs. Small interfering RNA analysis of CHS-A showed that the suppression resulted from post-transcriptional gene silencing (PTGS). Thus, it was hypothesized that the enhancement of anthocyanin biosynthetic gene expression due to P-deficiency triggered PTGS of CHS-A, which resulted in white corolla development.

Protective effect of extracts of Perilla frutescens treated with sucrose on tert-butyl hydroperoxide-induced oxidative hepatotoxicity in vitro and in vivo

Perilla frutescens leaves are often used in East Asian gourmet food. In this study, we investigated the hepatoprotective effects of P. frutescens leaves grown in different concentrations of sucrose (0, 115, 175 and 235 mM sucrose) leading to four samples of perilla leaf extracts (PLEs). Based on caffeic acid level and antioxidant activities, further experiments were conducted using perilla leaf extracts treated with 6% sucrose compared with non-treated perilla leaf extracts as a control. Oral intubation with non-treated perilla leaf extracts or perilla leaf extracts treated with 6% sucrose (1000 mg/kg b.w. rat) for 5 days was conducted before treatment with a single dose of tert-butyl hydroperoxide (0.5 mmol/kg b.w., i.p.) led to a significant reduction of hepatic toxicity in the perilla leaf extracts treated with 6% sucrose. We demonstrated that P. frutescens with higher contents of caffeic acid was produced, and that sucrose could play a role in the induction of this secondary metabolite. Sucrose-treated perilla leaves, which had better antioxidant activities than untreated leaves, can be used as a potential dietary source.

Increasing the source/sink ratio in Vitis vinifera (cv Sangiovese) induces extensive transcriptome reprogramming and modifies berry ripening

BACKGROUND

Cluster thinning is an agronomic practice in which a proportion of berry clusters are removed from the vine to increase the source/sink ratio and improve the quality of the remaining berries. Until now no transcriptomic data have been reported describing the mechanisms that underlie the agronomic and biochemical effects of thinning.

RESULTS

We profiled the transcriptome of Vitis vinifera cv. Sangiovese berries before and after thinning at veraison using a genome-wide microarray representing all grapevine genes listed in the latest V1 gene prediction. Thinning increased the source/sink ratio from 0.6 to 1.2 m2 leaf area per kg of berries and boosted the sugar and anthocyanin content at harvest. Extensive transcriptome remodeling was observed in thinned vines 2 weeks after thinning and at ripening. This included the enhanced modulation of genes that are normally regulated during berry development and the induction of a large set of genes that are not usually expressed.

CONCLUSION

Cluster thinning has a profound effect on several important cellular processes and metabolic pathways including carbohydrate metabolism and the synthesis and transport of secondary products. The integrated agronomic, biochemical and transcriptomic data revealed that the positive impact of cluster thinning on final berry composition reflects a much more complex outcome than simply enhancing the normal ripening process.

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.

Association between winter anthocyanin production and drought stress in angiosperm evergreen species

Leaves of many evergreen angiosperm species turn red under high light during winter due to the production of anthocyanin pigments, while leaves of other species remain green. There is currently no explanation for why some evergreen species exhibit winter reddening while others do not. Conditions associated with low leaf water potentials (Psi) have been shown to induce reddening in many plant species. Because evergreen species differ in susceptibility to water stress during winter, it is hypothesized that species which undergo winter colour change correspond with those that experience/tolerate the most severe daily declines in leaf Psi during winter. Six angiosperm evergreen species which synthesize anthocyanin in leaves under high light during winter and five species which do not were studied. Field Psi, pressure/volume curves, and gas exchange measurements were derived in summer (before leaf colour change had occurred) and winter. Consistent with the hypothesis, red-leafed species as a group had significantly lower midday Psi in winter than green-leafed species, but not during the summer when all the leaves were green. However, some red-leafed species showed midday declines similar to those of green-leafed species, suggesting that low Psi alone may not induce reddening. Pressure-volume curves also provided some evidence of acclimation to more negative water potentials by red-leafed species during winter (e.g. greater osmotic adjustment and cell wall hardening on average). However, much overlap in these physiological parameters was observed as well between red and green-leafed species, and some of the least drought-acclimated species were red-leafed. No difference was observed in transpiration (E) during winter between red and green-leaved species. When data were combined, only three of the six red-leafed species examined appeared physiologically acclimated to prolonged drought stress, compared to one of the five green-leafed species. This suggests that drought stress alone is not sufficient to explain winter reddening in evergreen angiosperms.

Identification and characterization of genes induced for anthocyanin synthesis and chlorophyll degradation in regenerated torenia shoots using suppression subtractive hybridization, cDNA microarrays, and RNAi techniques

Anthocyanin synthesis and chlorophyll degradation in regenerated torenia (Torenia fournieri Linden ex Fourn.) shoots induced by osmotic stress with 7% sucrose were examined to identify the genes regulating the underlying molecular mechanism. To achieve this, suppression subtractive hybridization was performed to enrich the cDNAs of genes induced in anthocyanin-synthesizing and chlorophyll-degrading regenerated shoots. The nucleotide sequences of 1,388 random cDNAs were determined, and these were used in the preparation of cDNA microarrays for high-throughput screening. From 1,056 cDNAs analyzed in the microarrays, 116 nonredundant genes were identified, which were up regulated by 7% sucrose to induce anthocyanin synthesis and chlorophyll degradation in regenerated shoots. Of these, eight genes were selected and RNAi transformants prepared, six of which exhibited anthocyanin synthesis inhibition and/or chlorophyll degradation in their leaf discs. Notably, the RNAi transformants of the glucose 6-phosphate/phosphate translocator gene displayed inhibition both of anthocyanin synthesis and chlorophyll degradation in both leaf discs and regenerated shoots. There was also less accumulation of anthocyanin in the petals, and flowering time was shortened. The genes we identified as being up-regulated in the regenerated torenia shoots may help further elucidate the molecular mechanism underlying the induction of anthocyanin synthesis and chlorophyll degradation.

Effect of ABA upon anthocyanin synthesis in regenerated torenia shoots

To elucidate the mechanism of anthocyanin synthesis induction concomitant with chlorophyll degradation, we established a system in which anthocyanin synthesis and degradation of chlorophyll in regenerated torenia (Torenia fournieri) shoots was induced on medium containing 7% sucrose. Here, we studied the effect of several plant-growth regulators on anthocyanin synthesis and the degradation of chlorophyll in the torenia shoot regenerating system. Exogenous abscisic acid (ABA) could induce anthocyanin synthesis and chlorophyll senescence in regenerating torenia shoots on the medium containing a low concentration of sucrose (1.5%). We determined the changes in the amount of endogenous ABA in the regenerated shoots during the process of anthocyanin synthesis on the medium containing 7% sucrose. It was revealed that the 7% sucrose treatment elevated endogenous ABA levels before the induction of anthocyanin synthesis and chlorophyll degradation. However, while retransfer to the 1.5% sucrose medium resulted in a gradual decrease in the ABA level and a failure of induction of anthocyanin synthesis, normal shoot regeneration. These results suggest that changes in the amount of endogenous ABA may play an important role in the induction of anthocyanin synthesis and chlorophyll degradation in regenerated torenia shoots.

High root biomass production in anchored Arabidopsis plants grown in axenic sucrose supplemented liquid culture

There are many benefits to growing Arabidopsis in solution-based media, especially when large amounts of root tissue are required for molecular and biochemical studies. Roots grown in soil are brittle and tend to break easily when removed from their substrate. We have developed an axenic liquid culture system that simplifies growing large amounts of roots from intact plants. This technique consists of germinating 15 seeds on 2.5 cm2 stainless steel screens placed on half-strength semisolid Murashige and Skoog medium containing 1% or 2% sucrose. The screens anchor and support the plantlets in an upright position while keeping the roots and shoots separate. The seedlings are transferred with forceps to 125-mL wide-mouth Erlenmeyer flasks containing 10 mL of half-strength Murashige and Skoog liquid medium and 1% sucrose. The flasks are placed onto a floor rotary shaker under fluorescent lights. After 3 days, the sucrose is increased to 3% and the volume to 15 mL for 7 days. During any further experimental manipulations, sucrose is not supplied. The media is changed every 3-4 days to replenish the nutrients. The presence of sucrose in the media dramatically increases the biomass, and large amounts of root tissue can easily be harvested.