Expression Of PSY Research Articles

Physiological response of microalga Dunaliella parva when treated with MeJA, GA3.

DpAP2 is a transcription factor regulating carotenoid biosynthesis pathway. It was speculated that MeJA significantly decreased expression of DpAP2 gene, then the decreasing DpAP2 expression significantly inhibited expression of some key enzyme genes such as PSY, PDS and GGPS in carotenoid biosynthesis pathway. In contrast, it was speculated that GA3 significantly increased expression of DpAP2 gene, then the increasing DpAP2 expression significantly increased expression of some key enzyme genes such as PDS and GGPS in carotenoid biosynthesis pathway. To increase the content of carotenoid, we evaluated the effect of DpAP2 overexpression on carotenoid accumulation in D. parva. Transgenic D. parva showed a higher carotenoid content (3.18 mg/g DW) compared with control group (2.13 mg/g DW) at 9 d. The dosage effects of exogenous hormones MeJA and GA3 were found in D. parva cells treated with different concentrations of MeJA (10, 20, 50, 100 μM) and GA3 (10, 20, 50, 100 μM). The high concentrations of MeJA (10-100 μM) inhibited the accumulation of carotenoid, and the relative expression of DpAP2, PSY, PDS and GGPS decreased significantly. On the contrary, the relative expression of DpAP2, PDS and GGPS increased significantly when D. parva was treated with 10, 20, 50 and 100 μM GA3, which promoted the biosynthesis of carotenoid. Therefore, we inferred that there was a hierarchical regulation from hormone, transcription factor, key enzyme gene to carotenoid accumulation in carotenoid biosynthesis. Carotenoid biosynthesis was enhanced by DpAP2 overexpression (1.4930 fold of control) and exogenous substances such as GA3 (1.5889 fold of control), which laid a foundation for massive accumulation of carotenoids in microalgae. In the future, further studies were required to demonstrate the complex regulatory network.

Effect of postharvest cold storage and subsequent shelf-life on fruit quality and endogenous phytohormones in nectarine fruit

Cold storage is the main approach to extend the postharvest storage period of nectarines. The objective of this study was to investigate fruit quality (flavor and nutrition) and endogenous phytohormone changes and their related transcriptional changes in nectarine fruit after cold storage and subsequent shelf-life, which was performed metabolome, transcriptome and physiological analysis. Cold storage led to irreversible flavor loss due to the inhibition of aroma biosynthesis genes at low temperature. Sugar and organic acid content was affected, with an increase in glucose, fructose and malic acid, and a decrease in sorbitol and citric acid after cold storage or shelf-life. For fruit nutritional quality, total flavonoids or total carotenoids was not significantly affected by cold storage, whereas shelf-life process enhanced their accumulation. The activities of key enzymes for flavonoid biosynthesis, PAL and C4H, were enhanced during the shelf-life process, resulting in a significant increase in flavonoids and enhanced free radicals scavenging capacity. Meanwhile, shelf-life process increased carotenoids content by improving the expression of carotenoid biosynthesis genes PSY, ZDS and ZISO. Additionally, cold storage significantly increased the IAA content and ethylene production, thereby inducing the up-regulation of related signaling transduction genes. The shelf-life process further increased ethylene production, as well as salicylic acid and jasmonic acid content. This study unravels these crucial physiological and associated transcriptional changes of nectarines after cold storage, and may provide a theoretical foundation for improving fruit quality of peaches after cold storage.

Effects of gamma irradiation treatment on ROS accumulation and carotenoid metabolism in postharvest Cara Cara fruit (Citrus sinensis L. Osbeck) during storage

This study evaluated the effect of low-dose gamma irradiation (0.3–0.9 kGy) on carotenoid accumulation in Cara Cara fruit (Citrus sinensis L. Osbeck) during storage. Additionally, the irradiation-induced ROS (reactive oxygen species) response and transcriptional levels of carotenoid biosynthesis genes were investigated. Immediate irradiation caused a temporary decrease in most carotenoid levels; however, values recovered during storage and were even higher than those of the control, particularly at 0.6 kGy, especially for carotenoid precursors and carotenes. The upregulated expression of psy, zds and lcyb during majority of the storage period, coupled with the strengthened interaction among adjacent carotenoids, might contribute to the enhanced accumulation of carotenoids in irradiated fruit. A highly positive correlation was found among ROS content, total carotenoids, and upstream expression of zds and lcyb, suggesting that the enhanced carotenoid content in irradiated Cara Cara fruits might be regulated by zds and lcyb in response to ROS accumulation. Antioxidant enzymes of APX, SOD, and CAT levels were significantly correlated with ROS accumulation. In summary, gamma irradiation (0.6 kGy) elevated the levels of carotenoids and antioxidant enzymes, which were potentially modulated by ROS in response to irradiation stress.

Comprehensive metabolome and transcriptome analyses demonstrate divergent anthocyanin and carotenoid accumulation in fruits of wild and cultivated loquats.

Eriobotrya is an evergreen fruit tree native to South-West China and adjacent countries. There are more than 26 loquat species known in this genus, while E. japonica is the only species yet domesticated to produce fresh fruits from late spring to early summer. Fruits of cultivated loquat are usually orange colored, in contrast to the red color of fruits of wild E. henryi (EH). However, the mechanisms of fruit pigment formation during loquat evolution are yet to be elucidated. To understand these, targeted carotenoid and anthocyanin metabolomics as well as transcriptomics analyses were carried out in this study. The results showed that β-carotene, violaxanthin palmitate and rubixanthin laurate, totally accounted for over 60% of the colored carotenoids, were the major carotenoids in peel of the orange colored 'Jiefangzhong' (JFZ) fruits. Total carotenoids content in JFZ is about 10 times to that of EH, and the expression levels of PSY, ZDS and ZEP in JFZ were 10.69 to 23.26 folds to that in EH at ripen stage. Cyanidin-3-O-galactoside and pelargonidin-3-O-galactoside were the predominant anthocyanins enriched in EH peel. On the contrary, both of them were almost undetectable in JFZ, and the transcript levels of F3H, F3'H, ANS, CHS and CHI in EH were 4.39 to 73.12 folds higher than that in JFZ during fruit pigmentation. In summary, abundant carotenoid deposition in JFZ peel is well correlated with the strong expression of PSY, ZDS and ZEP, while the accumulation of anthocyanin metabolites in EH peel is tightly associated with the notably upregulated expressions of F3H, F3'H, ANS, CHS and CHI. This study was the first to demonstrate the metabolic background of how fruit pigmentations evolved from wild to cultivated loquat species, and provided gene targets for further breeding of more colorful loquat fruits via manipulation of carotenoids and anthocyanin biosynthesis.

Integrated Metabolome and Transcriptome Analysis of Fruit Flavor and Carotenoids Biosynthesis Differences Between Mature-Green and Tree-Ripe of cv. "Golden Phoenix" Mangoes (Mangifera indica L.).

The commodity value of fruits is directly affected by fruit flavor and color. Secondary metabolites, such as amino acids, organic acids, esters, and β-carotene, are important synthetic products, which are of great significance in the flavor formation of mango fruits. In this study, a total of 309 different metabolites, consisting of organic acids, amino acids, phenolic acids, and saccharides, and a further 84 types of volatile organic compounds (VOCs) were identified in differential levels in TR vs. MG mango fruit stages. The major volatile compounds found were ester [2(3H)-furanone, 5-ethyldihydro; N-(2,5-ditrifluoromethylbenzoyl)-D-alanine, pentyl ester; and Octanoic acid, ethyl ester], aldehyde (benzaldehyde, 3-ethyl, and nonanal), and phenol [2-(1,1-dimethylethyl)-6-(1-methylethyl) phenol]. The analysis of carotenoid contents identified 68 carotenoids and we report for the first-time significant contents of zeaxanthin palmitate and (E/Z)-phytoene in mango fruits. α-carotene was a further major contributor to carotene contents with lesser contributions from 5,6epoxy-lutein-caprate-palmitate, β-carotene, lutein oleate, and β-cryptoxanthin. What is more, lutein content was significantly decreased in TR vs. MG fruit. RT-qPCR analysis revealed that relative to the MG stage, the expression of carotenogenic genes GGPS, PSY, LCYB, and ZEP was downregulated in TR mango fruit, whereas the transcript levels of PSD, CHYB, and NCED were downregulated. Additionally, the transcription level of some transcription factors (MYB, bHLH, and NAC) was highly correlated with pigment content in the pulp and may be responsible for carotenoid accumulation. The results describe major differences in metabolic pathways during the transition from MG to the TR stage of fruit ripening that are likely to contribute alterations in fruit flavor and provide several associated genes to be further studied in mango fruit.

Enhancement of carotenoid production and its regulation in edible mushroom Cordyceps militaris by abiotic stresses

Cordyceps militaris carotenoids are widely used as food additives, animal feed supplements, and so on. However, the biosynthetic pathway of carotenoids in C. militaris is still obscure. In this paper, changes of mycelial morphology and carotenoid accumulation of C. militaris were investigated under oxidative (KMnO4) and osmotic stress (NaCl). Subsequently, qRT-PCR was employed to detect the expression levels of genes related to carotenogenesis to explore the mechanism of adaptation to abiotic stress. When the concentrations of KMnO4 and NaCl were respectively 0.4 g/L and 2 g/L, carotenoid accumulation reached a maximum of 6616.82 ± 666.43 μg/g and 6416.77 ± 537.02 μg/g. Under the oxidative stress condition of KMnO4, the expressions of psy and hsp70 increased significantly compared with control. Besides, the genes fus3 and hog1 were significantly enriched in the MAPK signal pathway. Compared with the control group, there was no significant difference in expression of psy in the NaCl group. Moreover, the accumulation of triacylglycerols may contribute significantly to the increase in carotenoid accumulation. The increased accumulation of antioxidant carotenoids induced under environmental stress is to resist oxidative conditions. Fus3 and Hog1 signaling in the MAPK pathway was activated and subsequently take effects on the resistance of oxidative condition by regulating related metabolic processes. C. militaris resist the stress of high oxygen by producing a large amount of glycerol and carotenoids when this fungus is cultured in a saline environment for a long time.

Reactive oxygen species derived from NADPH oxidase regulate astaxanthin and total fatty acid accumulation in Chromochloris zofingiensis

Many abiotic stresses can promote astaxanthin and total fatty acid (TFA) accumulation in microalgae, but their signal molecules remain undetermined. The reactive oxygen species (ROS) derived from NADPH oxidase has been reported to act as signals and regulate many cellular responses in cell responses to biotic and abiotic stresses in higher plants. The present study explored the regulatory effects of NADPH oxidase derived ROS on astaxanthin and TFA accumulation in the green alga Chromochloris zofingiensis under nitrogen starvation. Diphenylene iodonium (DPI) inhibition of NADPH oxidase significantly decreased the cellular ROS level under nitrogen starvation. This was accompanied with the decreasing of astaxanthin and secondary carotenoids content, and the increasing of primary carotenoids content. Molecular studies showed that DPI depressed the expression of PSY, LCYb, and BKT, but elevated that of LCYe, which were coordinated with carotenoids content. Meanwhile, the TFA and neutral lipid contents, and the expression of their key biosynthesis genes, ACCase and PDAT, were also reduced in the DPI-treated cells. Additionally, the addition of ROS scavenger, N-acetylcysteine (NAC), decreased the astaxanthin and TFA contents. Taken together, our results revealed that NADPH oxidase-derived ROS was the key regulator in astaxanthin and fatty acid accumulation under nitrogen starvation.

RNAi silenced ζ-carotene desaturase developed variegated tomato transformants with increased phytoene content

ζ-carotene desaturase (ZDS) is one of the enzymes that catalyzes the conversion of ζ-carotene to lycopene. However, the role of ZDS has been not studied extensively in tomato. In this study, to examine the role of ZDS in tomato, the expression of ZDS was downregulated by RNA interference. The relative mRNA levels of ZDS in RNAi lines were reduced by more than 75% compared to wild-type plants. The genetically modified plants exhibited altered morphological characteristics such as photobleached leaves, increased leaf length, longer petioles, larger leaf surface areas and whitish-green tomato fruits. Chromatographic determination showed a significant increase in phytoene in both leaves and fruits of the RI lines, whereas other types of carotenoids were significantly decreased compared to controls. qPCR analysis revealed significant changes in the expression of PSY, PDS and LCYB. The endogenous hormones and flavonoid levels were altered in leaves and fruits of ZDS-silenced plants. Electron microscopic studies revealed hampered chloroplast differentiation and disrupted thylakoid structure in the ZDS-suppressed lines. GC–MS analysis showed that the level of several organic acids, amino acids and fatty acids were decreased in the RI lines, whereas the sugars and sugar derivatives were slightly increased compared to controls. Thus, these results imply a potential for ZDS in carotenoid enhancement through genetic engineering of the carotenoid pathway.

Changes in the carotenoids profile of two yellow-fleshed kiwifruit cultivars during storage

Abstract Carotenoid level in fruit changes dynamically in response to storage condition, however, the underlying mechanism remains unclear. Here, we investigated the carotenoid profiles and associated gene expression to reveal its responses to different storage temperature (20 °C and 4 °C) in two kiwifruit cultivars, bright-yellow-fleshed Jinshi 1 and pale-yellow-fleshed Jinyan. At harvest, four main carotenoids were detected in cv. Jinshi 1, while only three in cv. Jinyan, excluding β-cryptoxanthin, which accounted for the majority of carotenoids in ‘Jinshi 1’. Storage at 20 °C increased content of the total carotenoid and β-carotene in both cultivars, and up-regulated the expression of biosynthesis gene PSY, but down-regulated the expression of carotenoid degradation genes CCD1 and NCED1. It also induced β-cryptoxanthin and α-carotene production in Jinyan at later stage. On the contrary, storage at 4 °C decreased total carotenoid content, but induced the expression of carotenoid biosynthetic gene PDS, LCYB, LCYE. These results suggested expression of PSY, CCD1 and NCED1 plays an important role in improvement of carotenoids level at 20 °C. Furthermore, high proportion of β-cryptoxanthin might contribute to yellower flesh in Jinshi 1.

Fruit abortion of ‘Guifei’ mango (Mangifera indicaL.) affected biosynthesis of carotenoid and polyphenols in pulp

To investigate the effects of embryo abortion on fruit size and weight, fruit quality, chlorophyll, carotenoid, anthocyanin, flavonoid, and total polyphenols, the seeded fruit of mango (Mangifera indica L.) cultivar 'Guifei' were compared at the ripe stage. Seedless fruit had significantly smaller fruit size and lower fruit weight than seeded fruit in the cultivar. The experimental results suggested that embryo abortion at early stages of fruit ripening did not affect the concentration of total polyphenols in the pulp of matured fruit at green color or yellow color stages. However, the chlorophyll level decreased with ripening, lower in the abortion mango than in the normal mango. Carotenoid content increased throughout yellow stage and was significantly higher in the normal fruit compared to the abortion fruit. The concentrations of flavonoid were lower in the abortion fruit compared with normal fruit in the same color fruit. The expression of PSY and PDS was increased from green to yellow in abortion and normal mango. Expression of ANS and DFR was higher in the green color mango, in different development stages, and lower at the abortion stage in the yellow mango.

Glucose triggers cell structure changes and regulates astaxanthin biosynthesis in Chromochloris zofingiensis

Heterotrophic cultivation of Chromochloris zofingiensis is considered as a promising means of astaxanthin production; however, the astaxanthin content in heterotrophic cells is generally lower than that in photoautotrophic cells. To address this issue, the regulatory effects of glucose on astaxanthin accumulation were investigated. We found that glucose could increase astaxanthin accumulation by elevating the gene expression of PSY, LCYb, CHYb and BKT within 24 h; however, after 24 h, expression of those genes in the control group was higher than that in the glucose group, leading to an increased astaxanthin content in the control group after 48 h. At 96 and 192 h, the astaxanthin contents in the control group were 1.26 and 1.27 times of those in the glucose group, respectively. Further investigation showed that, glucose treatment triggered a decrease in chlorophylls content, caused degradation of chloroplasts at 24 h, which may be the reason for the above variation in gene expression and that in astaxanthin accumulation. Moreover, glucose also caused a slight increase in total fatty acid content and altered cellular lipid composition. Collectively, these findings suggested that glucose may regulate astaxanthin accumulation through its influence on cell structure.

Light induces carotenoids accumulation in a heterotrophic docosahexaenoic acid producing microalga, Crypthecodinium sp. SUN

In the present study, the effect of various light conditions on carotenoid accumulation in a novel heterotrophic microalga, Crypthecodinium sp. SUN was investigated. The results showed that C. sp. SUN mainly produced γ-carotene and β-carotene. The total carotenoid content could reach to 12.8 mg g−1 dry weight under high light intensity (100 μmol m−2 s−1), which was >100-fold higher than that under dark condition. Besides, along with the light intensity increased, the ROS level in vivo was decreased at 48 h and 72 h. Further study showed that, light could efficiently promote the gene expression of PSY and LCYb, which explain the molecular mechanisms of carotenoids accumulation under light conditions. Meanwhile, slightly inhibited fatty acids accumulation could promote the carotenoids yield. The present work proposed that C. sp. SUN could be a potential carotenoid producer, and provided valuable insight for carotenoids biosynthesis.

Effect of UV-B radiation and a supplement of CaCl2 on carotenoid biosynthesis in germinated corn kernels.

This study investigated effects of UV-B radiation and CaCl2 on the enhancement of carotenoid content in germinated corn kernels. UV-B radiation and CaCl2 treatments were effective for promoting both carotenoid content and antioxidant activity. Furthermore, the carotenoid content was greater when under the combined treatments of UV-B radiation and CaCl2. Activities of superoxide dismutase and peroxidase were enhanced but malondialdehyde content was weakened by UV-B radiation plus CaCl2 compared to the UV-B radiation only. The mRNA expression of PSY, PDS, ZDS, LCYB, LCYE, BCH1, CYP97C genes involved in the carotenoid biosynthesis pathway showed different patterns in UV-B radiation and CaCl2 treatments. This reveals that the UV-B radiation can increase carotenoid content and antioxidant enzyme activity. Moreover, CaCl2 can further improve carotenoid content and reduce photooxidative damage caused by UV-B radiation.

A new approach to promote astaxanthin accumulation via Na2WO4 in Haematococcus pluvialis

The optimum concentration of Na2WO4 was explored in relation to the cell density and astaxanthin content in Haematococcus pluvialis. Then, the cellular morphology, nitrate reductase (NR) activity, soluble sugar and protein contents, and chlorophyll fluorescence were measured, and the transcriptional expression of carotenogenic genes was determined by quantitative real-time PCR. The results showed that 3.0 mmol/L of Na2WO4 was the optimum concentration to induce astaxanthin accumulation, with a maximum content of 49.41±0.13 pg/cell reached on the tenth day. The NR activity decreased significantly and continually after Na2WO4 treatment. The soluble sugar content increased gradually during the experimental period and was eventually significantly higher than that in the control. The soluble protein content increased rapidly, reached a maximum in day 0.5 and day 1 and then decreased. The effective photochemical efficiency of PSII ( Fv'/Fm') and light saturation ( Ek) first decreased and then tended to stabilize, and NADP+-glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene expression was correlated with photosynthesis. The transcriptional expression of ipi, psy and bkt was significantly increased compared with that in the control after application of Na2WO4, and the relative expression of ipi reached the highest level on the fifth day, with a 98.03±1.92-fold increase. Our results describe a new approach to promote the effective accumulation of astaxanthin in H. pluvialis by NR inhibitor Na2WO4.

Effect of bagging duration on peach fruit peel color and key protein changes based on iTRAQ quantitation

The present study aimed to investigate the effect of bagging duration on the changes in the color and protein profiles in the fruit peel of the honey peach (Prunus persica ‘Hujingmilu’) using iTRAQ techniques. Peach fruits were bagged at 50 days after flowering (DAF), and the bags were removed at 90 (treatment I, short-duration bagging) or 105 (treatment II, long-duration bagging) DAF. Peach fruits used for this experiment were harvested at 50 DAF, 90 DAF, 95 DAF, and 105 DAF, and were stored for 3 days post-picking at 105 DAF. The chlorophyll, anthocyanin, carotenoid, zeaxanthin, and lycopene contents were determined and the key proteins were investigated using iTRAQ techniques. The peach peel color was regulated by chlorophyll degradation, carotenoid metabolism, and anthocyanin metabolism pathways both during development and postharvest. Shortening the bagging duration period could improve the red color and anthocyanin content of peach peel and maintain the stability of anthocyanins, but reduce peel brightness and chlorophyll content. Compared to treatment II, the expression of LHCAB protein and other related proteins in peach peel were not down-regulated in treatmentⅠduring the development but the chlorophyll content was lower of treatmentⅠthan treatment II; It could promote chlorophyll degradation by up-regulating PPR and PAO and not down-regulating LHCAB proteins at 108 DAF. Shortening bagging duration could increase the anthocyanin content, However, the expression of ANS, ANR, 3 G T, and CHS was unaffected at 105 DAF, which could inhibit the degradation of anthocyanin by up-regulating the expression of CHS at 108 DAF. Shortening bagging duration could inhibit the accumulation of carotenoid in peach peel by down-regulating the expression of PSY from 105 to 108 DAF, and decrease the carotenoid content by up-regulating CCD 4 at 108 DAF. The key proteins of peach peel color metabolism during development were LHCAB, PPR, PAO, 3 G T, ANS, and CCD 4; shortening the bagging duration period could affect this by regulating PAO, 3 G T, CHS and CCD 4.

Carotenoid accumulation and expression of carotenoid biosynthesis genes in mango flesh during fruit development and ripening

Abstract In order to investigate the regulation mechanisms of carotenoid biosynthesis in mango flesh, carotenoid content and the expression patterns of 15 carotenogenic gene in flesh of two mango cultivars ‘Tainong1’and ‘Hongyu’ were analsyed during fruit development and ripening. Carotenoid were increasingly accumulated during fruit growth and sharply incaresed during postharvest ripening in both cultivars. In ripe fruit, total carotenoid content in the flesh of ‘Tainong1’ was 177.16 ug/g (Fresh weight) FW, and for ‘Hongyu’ 36.24 ug/gFW. The major carotenoids in the flesh were β-Carotene and α-carotene,with minor carotenoids being β-cryptoxanthin, zeaxanthin, lutin and neoxanthin. RT-PCR analysis revealed that the expression of carotenogenic genes CRTISO, PSY, ZDS, BCH and ZEP were up-regulated in flesh, whereas the transcript levels of LCYB, LCYE and NCED were down-regulated in two cultivars and during fruit development and ripening. CRTISO, PSY, ZDS, BCH and ZEP transcripts were significantly positively correlated with the total carotenoids content, while no differences were detected for CRTISO expression between cultivars. These results suggested that PSY, ZDS, BCH and ZEP coordinately contribute to carotenoid accumulation during mango fruit development and ripening.

Phytoremediation of petroleum-contaminated soil by Salicornia: from PSY activity to physiological and morphological communications

ABSTRACTPetroleum is one of the critical environmental pollutants. Salicornia can grow in petroleum-contaminated soil. Therefore, the potential of two Iranian Salicornia species, S. persica Akhani and S. iranica Akhani, for phytoremediation of soils contaminated with 0.2% or 2% petroleum was evaluated over short (1 and 10 h) and long (100 days) periods of time. In addition, some key factors including the expression analysis of phytoene synthase, physiological and morphological factors were studied. Both species reduced the petroleum in 0.2% and 2% petroleum-contaminated soils to 40% and 60% of the initial amount, respectively. The expression of PSY increased twice more than the control 10 h after 0.2% petroleum stress and the carotenoid content increased twice more than the control. Chlorophyll a and total chlorophyll decreased three times less than the control in both contamination levels, while chlorophyll b decreased three times less than the control only in 2% contamination. The proline content peaked 10 h after 2% stress as it was 10 times more than the control. Promoter analysis of PSY showed the existence of responsive cis-acting elements to abscisic acid suggesting the key role of this gene in abiotic stresses.

Inhibition of autophagy modulates astaxanthin and total fatty acid biosynthesis in Chlorella zofingiensis under nitrogen starvation

The present study showed that inhibition of autophagy significantly increased cellular levels of reactive oxygen species in Chlorella zofingiensis under nitrogen starvation. This was accompanied with increased expression of PSY, and enhanced accumulation of astaxanthin after 48h of cultivation. Nevertheless, the proportion of astaxanthin in secondary carotenoids remained unchanged. Meanwhile, the expression level of ACCase was also elevated in the 3-MA-treated cells compared to the control despite a >20% lower content of fatty acid in the former than the latter. This phenomenon might be due to inhibition of recycling of cellular components by 3-MA and suggests the potential involvement of post-transcriptional regulation in fatty acid biosynthesis. In summary, our work has been the first to report a potentially important role of autophagy in fatty acid and astaxanthin accumulation in C. zofingiensis under stress conditions. The findings might provide valuable insights to guide further research in this area.

Isolation and characterization of the carotenoid biosynthetic genes LCYB, LCYE and CHXB from strawberry and their relation to carotenoid accumulation

Carotenoids are common pigments in yellow, orange and red fruits, and their compositions and contents are important indexes to evaluate the nutritional and commercial values of the fruits. To investigate the transcriptional regulation of carotenoid biosynthesis genes in relation to carotenoid accumulation during strawberry development, three cDNAs (LCYB, LCYE and CHXB) that encode carotenoid biosynthesis downstream enzymes (lycopene β-cyclase, lycopene ɛ-cyclase and β-ring hydroxylase) were isolated in the present study. Carotenoid accumulation and the expression of these genes along with three previously cloned upstream genes, PSY, PDS and ZDS, were analyzed. The data confirmed that the dominant carotenoids that accumulate in strawberries are lutein and β-carotene, and their contents varied with genotypes and decreased during fruit development. The expression analysis of carotenoid biosynthetic genes revealed that the pattern of upstream genes was opposite that of downstream genes. In contrast to the increased expression of PSY, PDS and ZDS, the decreased expression of LCYB, LCYE and CHXB correlated more closely with carotenoid accumulation in strawberries. Moreover, the expression profiles of LCYB and LCYE were consistent with the changes observed in β-carotene and lutein, respectively. These results suggested that the changes in genes expression related to carotenoid contents varied during strawberry development. In particular, LCYB and LCYE appeared to be the key regulatory genes for carotenoid accumulation in strawberries.

Ectopic expression of a fruit phytoene synthase from Citrus paradisi Macf. promotes abiotic stress tolerance in transgenic tobacco

Abscisic acid (ABA) is an important regulator of plant responses to environmental stresses and an absolute requirement for stress tolerance. Recently, a third phytoene synthase (PSY3) gene paralog was identified in monocots and demonstrated to play a specialized role in stress-induced ABA formation, thus suggesting that the first committed step in carotenogenesis is a key limiting step in ABA biosynthesis. To examine whether the ectopic expression of PSY, other than PSY3, would similarly affect ABA level and stress tolerance, we have produced transgenic tobacco containing a fruit-specific PSY (CpPSY) of grapefruit (Citrus paradisi Macf.). The transgenic plants contained a single- or double-locus insertion and expressed CpPSY at varying transcript levels. In comparison with the wild-type plants, the CpPSY expressing transgenic plants showed a significant increase on root length and shoot biomass under PEG-, NaCl- and mannitol-induced osmotic stress. The enhanced stress tolerance of transgenic plants was correlated with the increased endogenous ABA level and expression of stress-responsive genes, which in turn was correlated with the CpPSY copy number and expression level in different transgenic lines. Collectively, these results provide further evidence that PSY is a key enzyme regulating ABA biosynthesis and that the altered expression of other PSYs in transgenic plants may provide a similar function to that of the monocot's PSY3 in ABA biosynthesis and stress tolerance. The results also pave the way for further use of CpPSY, as well as other PSYs, as potential candidate genes for engineering tolerance to drought and salt stress in crop plants.