Pigment variation and transcriptional response of the pigment synthesis pathway in the S2309 triple-color ornamental kale (Brassica oleracea L. var. acephala) line

Ornamental kale is popular because of its colorful leaves and few studies have investigated the mechanism of color changes. In this study, an ornamental kale line (S2309) with three leaf colors was developed. Analysis of the anthocyanin, chlorophyll, and carotenoid contents and RNA-seq were performed on the three leaf color types. There was less chlorophyll in the white leaves and purple leaves than in the green leaves, and the anthocyanin content was greatest in the purple leaves. All the downregulated DEGs related to chlorophyll metabolism were detected only in the S2309_G vs. S2309_W comparison, which indicated that the decrease in chlorophyll content was caused mainly by the inhibition of chlorophyll biosynthesis during the leaf color change from green to white. Moreover, the expression of 19 DEGs involved in the anthocyanin biosynthesis pathway was upregulated. These results provide new insight into the mechanisms underlying the three-color formation.     

Linkage of the <Emphasis Type="Italic">A</Emphasis> locus for the presence of anthocyanin and <Emphasis Type="Italic">fs10.1</Emphasis>, a major fruit-shape QTL in pepper

The purple color of the foliage, flower and immature fruit of pepper ( Capsicum spp.) is a result of the accumulation of anthocyanin pigments in these tissues. The expression of anthocyanins is controlled by the incompletely dominant gene A. We have mapped A to pepper chromosome 10 in a Capsicum annuum (5226) x Capsicum chinense (PI 159234) F(2) population to a genomic region that also controls anthocyanin expression in two other Solanaceous species, tomato and potato, suggesting that variation for tissue-specific expression of anthocyanin pigments in these plants is controlled by an orthologous gene(s). We mapped an additional locus, Fc, for the purple anther filament in an F(2) population from a cross of IL 579, a C. chinense introgression line and its recurrent parent 100/63, to the same position as A, suggesting that the two loci are allelic. The two anthocyanin loci were linked to a major quantitative trait locus, fs10.1, for fruit-shape index (ratio of fruit length to fruit width), that also segregated in the F(2) populations. This finding verified the observation of Peterson in 1959 of linkage between fruit color and fruit-shape genes in a cross between round and elongated-fruited parents. The linkage relationship in pepper resembles similar linkage in potato, in which anthocyanin and tuber-shape genes were found linked to each other in a cross of round and elongated-tuber parents. It is therefore possible that the shape pattern of distinct organs such as fruit and tuber in pepper and potato is controlled by a similar gene(s).     

花青素调节基因VlmybA2对番茄遗传转化

以小型番茄 Micro-Tom 为材料,利用农杆菌介导法导入花青素调节基因VlmybA2。对抗性筛选出的再生植株进行 GUS 组织染色和 PCR 检测,证明外源基因已经整合到 Micro-Tom 中,转基因番茄根、茎、叶脉、果皮均呈紫色,花色为黄紫嵌合。而野生型的根为白色,茎、叶脉呈绿色,果皮为红色,花为黄色。对转基因番茄的花青素含量、叶片叶绿素含量和光合速率等生理指标进行测定,花青素含量有显著增加,叶绿素含量降低,VlmybA2基因过量表达会降低植株的光合效率,但对植株正常生长影响并不显著。VlmybA2 基因既可增加抗衰老物质花青素含量,又可作为转基因植株的报告基因。     

Manipulation of the blue light photoreceptor cryptochrome 2 in tomato affects vegetative development, flowering time, and fruit antioxidant content

Cryptochromes are blue light photoreceptors found in plants, bacteria, and animals. In Arabidopsis, cryptochrome 2 (cry2) is involved primarily in the control of flowering time and in photomorphogenesis under low-fluence light. No data on the function of cry2 are available in plants, apart from Arabidopsis (Arabidopsis thaliana). Expression of the tomato (Solanum lycopersicum) CRY2 gene was altered through a combination of transgenic overexpression and virus-induced gene silencing. Tomato CRY2 overexpressors show phenotypes similar to but distinct from their Arabidopsis counterparts (hypocotyl and internode shortening under both low- and high-fluence blue light), but also several novel ones, including a high-pigment phenotype, resulting in overproduction of anthocyanins and chlorophyll in leaves and of flavonoids and lycopene in fruits. The accumulation of lycopene in fruits is accompanied by the decreased expression of lycopene beta-cyclase genes. CRY2 overexpression causes an unexpected delay in flowering, observed under both short- and long-day conditions, and an increased outgrowth of axillary branches. Virus-induced gene silencing of CRY2 results in a reversion of leaf anthocyanin accumulation, of internode shortening, and of late flowering in CRY2-overexpressing plants, whereas in wild-type plants it causes a minor internode elongation.     

Functional Characterization of Dihydroflavonol-4-Reductase in Anthocyanin Biosynthesis of Purple Sweet Potato Underlies the Direct Evidence of Anthocyanins Function against Abiotic Stresses

Dihydroflavonol-4-reductase (DFR) is a key enzyme in the catalysis of the stereospecific reduction of dihydroflavonols to leucoanthocyanidins in anthocyanin biosynthesis. In the purple sweet potato (Ipomoea batatas Lam.) cv. Ayamurasaki, expression of the IbDFR gene was strongly associated with anthocyanin accumulation in leaves, stems and roots. Overexpression of the IbDFR in Arabidopsis tt3 mutants fully complemented the pigmentation phenotype of the seed coat, cotyledon and hypocotyl. Downregulation of IbDFR expression in transgenic sweet potato (DFRi) using an RNAi approach dramatically reduced anthocyanin accumulation in young leaves, stems and storage roots. In contrast, the increase of flavonols quercetin-3-O-hexose-hexoside and quercetin-3-O-glucoside in the leaves and roots of DFRi plants is significant. Therefore, the metabolic pathway channeled greater flavonol influx in the DFRi plants when their anthocyanin and proanthocyanidin accumulation were decreased. These plants also displayed reduced antioxidant capacity compared to the wild type. After 24 h of cold treatment and 2 h recovery, the wild-type plants were almost fully restored to the initial phenotype compared to the slower recovery of DFRi plants, in which the levels of electrolyte leakage and hydrogen peroxide accumulation were dramatically increased. These results provide direct evidence of anthocyanins function in the protection against oxidative stress in the sweet potato. The molecular characterization of the IbDFR gene in the sweet potato not only confirms its important roles in flavonoid metabolism but also supports the protective function of anthocyanins of enhanced scavenging of reactive oxygen radicals in plants under stressful conditions.     

Protection mechanisms against excess light in the resurrection plants Craterostigma wilmsii and Xerophyta viscosa

Mechanisms of avoidance and protection against light damage were studied in the resurrection plants Craterostigma wilmsii and Xerophyta viscosa.In C. wilmsii, a combination of both physical and chemical changes appeared to afford protection against free radical damage. During dehydration leaves curled inwards, and the abaxial surface became exposed to light. The tissue became purple/brown in colour, this coinciding with a three-fold increase in anthocyanin content and a 30% decline in chlorophyll content. Thus light-chlorophyll interactions are progressively reduced as chlorophyll became masked by anthocyanins in abaxial layers and shaded in the adaxial layers. Ascorbate peroxidase (AP) activity increased during this process but declined when the leaf was desiccated (5% RWC). During rehydration leaves uncurled and the potential for normal light-chlorophyll interaction was possible before full hydration had occurred. Superoxide dismutase (SOD) and glutathione reductase (GR) activities increased markedly during this stage, possibly affording free radical protection until full hydration and metabolic recovery had occurred.In contrast, the leaves of X. viscosa did not curl, but light-chlorophyll interactions were minimised by the loss of chlorophyll and dismantling of thylakoid membranes. During dehydration, free radical protection was afforded by a four-fold increase in anthocyanin content and increased activities of AP, GR and SOD. These declined during rehydration. It is suggested that potential free radical damage may be avoided by the persistence of anthocyanins during the period of thylakoid membrane re-assembly and full chlorophyll restitution which only occurred once the leaves were fully rehydrated.     

Effects of leaf wetting and high humidity on stomatal function in leafy cuttings and intact plants of Corylus maxima

When rooted cuttings of Corylus maxima Mill. cv. Purpurea are moved from the wet and humid conditions of the rooting environment, the leaves frequently shrivel and die. Since the newly formed adventitious root system has been shown to be functional in supplying water to the shoot, stomatal behaviour in C. maxima was investigated in relation to the failure to prevent desiccation. Stomatal conductance (g_s) in expanding leaves (L3) of cuttings increased almost 10-fold over the first 14 days in the rooting environment (fog), from 70 to 650 mmol m⁻² s⁻¹. In contrast, g_s of expanded leaves (L1) changed little and was in the region of 300 mmol m⁻² s⁻¹. Midday leaf water potential was much higher in cuttings than in leaves on the mother stock-plant (−0.5 versus −1.2 MPa) even before any roots were visible. Despite this, leaf expansion of L3 was inhibited by >50% in cuttings and stomata showed a gradual reduction in their ability to close in response to abscisic acid (ABA). To determine whether the loss of stomatal function in cuttings was due to severance or to unnaturally low vapour pressure deficit and wetting in fog, intact plants were placed alongside cuttings in the rooting environment. The intact plants displayed reductions in leaf expansion and in the ability of stomata to close in response to dark, desiccation and ABA. However, in cuttings, the additional effect of severance resulted in smaller leaves than in intact plants and more severe reduction in stomatal closure, which was associated with a 2.5-fold increase in stomatal density and distinctively rounded stomatal pores. The similarities between stomatal dysfunction in C. maxima and that observed in many species propagated in vitro are discussed, as is the possible mechanism of dysfunction.     

Methyl jasmonate induces anthocyanin accumulation in <Emphasis Type="Italic">Gynura bicolor</Emphasis> cultured roots

Gynura bicolor DC., a traditional vegetable in Japan, is cultivated as Kinjisou and Suizenjina in Ishikawa and Kumamoto prefectures, respectively. The adaxial side of the leaves of G. bicolor grown in a field is green, and the abaxial side is reddish purple. It has been reported that these reddish purple pigments are anthocyanins. Although we established a culture system of G. bicolor, the leaves of G. bicolor plants grown under our culture conditions showed green color on both sides of all leaves. We investigated the effects of phytohormones and chemical treatments on anthocyanin accumulation in cultured plants. Although anthocyanin accumulation in the leaves was slightly stimulated, anthocyanins accumulation in the roots of the cultured plant was induced remarkably by 25–50 μM methyl jasmonate (MJ) treatment. This induction was affected by light irradiation and sucrose concentration in the culture medium. However, salicylic acid (SA) and 1-aminocyclopropane-1-carboxylic acid did not induce anthocyanin accumulation in roots. And then, combinations of MJ and SA or MJ and AgNO₃ did not stimulate the anthocyanin accumulation in the root as found in the case of treatment by MJ solely.     

Red leaf color as a warning signal against insect herbivory: Honest or mimetic?

The co-evolution theory for red leaf colors considers redness as a handicap signal against herbivory. We have examined whether the assumed signal is honest and, accordingly, costly, by seeking a correlation between anthocyanin and total phenolic levels in 11 plants exhibiting variation in the expression of the red character either between individuals or between modules on the same individual. Selection of total phenolics as a variable was based on their assumed anti-herbivore function and on their common biosynthetic origin with anthocyanins. Plants with young or senescing red leaves were tested. Confirming evidence was found in senescing leaves, where in three out of the four studied species a significant and strongly positive correlation between signal strength (redness) and actual defensive potential (total phenolics) was found, rendering the signal both honest and costly. In young, developing leaves a significant, yet weakly positive correlation was found only in three out the seven examined species. Accordingly, the handicap signal hypothesis may be questioned in the case of young leaves. Hence, young leaf redness fits more to the alternative hypotheses that red leaf color is less easily perceived by folivorous insect photoreceptors or that red leaf color undermines insect camouflage. These hypotheses do not demand an increased chemical defensive potential.