IMPROVED DETECTION AND CHARACTERIZATION OF FUCOXANTHIN‐TYPE CAROTENOIDS: NOVEL PIGMENTS IN EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE)1

A new atmospheric pressure chemical ionization mass spectrometry (APCI‐LC/MS) method improved detection and aided characterization of fucoxanthin related carotenoids, revealing the coccolithophorid Emiliania huxleyi (Lohm.) Hay et Mohler (strain MBA 92, Plymouth) to contain a wider range of acyloxyfucoxanthins than reported previously. The diversity is confirmed as arising from differences in the length of the alkanoic acid substituent esterified at position C‐19′. Acyloxyfucoxanthins with substituents of between four and eight carbons at the C‐19′ position have been detected in a culture of Emiliania huxleyi, where previously only 19′‐butanoyloxyfucoxanthin and 19′‐hexanoyloxyfucoxanthin have been reported in the literature. Novel fucoxanthinol derivatives were also found. The detection of these novel carotenoids in Emiliania huxleyi permits detailed studies of the impact of environmental factors on individual components of the complex pool of fucoxanthin‐type carotenoids in this organism.     

鸟类羽毛色素的合成机理与调控机制

鸟类作为色彩最丰富的陆生脊椎动物,其体表覆盖着颜色多样的羽毛,在伪装、择偶、信号识别等多方面具有重要功能,因此羽毛颜色引起了研究者的极大兴趣。羽毛颜色总体分为由化学物质产生的色素色和由物理结构产生的结构色,其中常见色素有两大类。根据近年来对羽毛色素的研究进展,本文总结了黑色素和类胡萝卜素的类型、合成途径、获取途径以及相关基因,为深入研究羽毛色素合成、代谢的分子调控机制提供科学依据。     

Utilization of Dioxygen by Carotenoid Cleavage Oxygenases

Carotenoid cleavage oxygenases (CCOs) are non-heme, Fe(II)-dependent enzymes that participate in biologically important metabolic pathways involving carotenoids and apocarotenoids, including retinoids, stilbenes, and related compounds. CCOs typically catalyze the cleavage of non-aromatic double bonds by dioxygen (O₂) to form aldehyde or ketone products. Expressed only in vertebrates, the RPE65 sub-group of CCOs catalyzes a non-canonical reaction consisting of concerted ester cleavage and trans-cis isomerization of all-trans-retinyl esters. It remains unclear whether the former group of CCOs functions as mono- or di-oxygenases. Additionally, a potential role for O₂ in catalysis by the RPE65 group of CCOs has not been evaluated to date. Here, we investigated the pattern of oxygen incorporation into apocarotenoid products of Synechocystis apocarotenoid oxygenase. Reactions performed in the presence of ¹⁸O-labeled water and ¹⁸O₂ revealed an unambiguous dioxygenase pattern of O₂ incorporation into the reaction products. Substitution of Ala for Thr at position 136 of apocarotenoid oxygenase, a site predicted to govern the mono- versus dioxygenase tendency of CCOs, greatly reduced enzymatic activity without altering the dioxygenase labeling pattern. Reevaluation of the oxygen-labeling pattern of the resveratrol-cleaving CCO, NOV2, previously reported to be a monooxygenase, using a purified enzyme sample revealed that it too is a dioxygenase. We also demonstrated that bovine RPE65 is not dependent on O₂ for its cleavage/isomerase activity. In conjunction with prior research, the results of this study resolve key issues regarding the utilization of O₂ by CCOs and indicate that dioxygenase activity is a feature common among double bond-cleaving CCOs.     

Effects of iron on growth and reflectance spectrum of the bloom‐forming cyanobacterium Microcystis viridis

Iron is an important factor in algal blooms because it is involved in cyanobacterial pigment biosynthesis and therefore has the ability to influence the pigment status of algal cells. This role in pigment biosynthesis offers the opportunity for rapid monitoring of iron availability to cyanobacteria through spectral reflectance characterization. In the present study, the freshwater cyanobacterium Microcystis viridis was cultured with different levels of iron. Cell density, cellular content of iron and photosynthetic pigments, and spectral reflectivity of M. viridis were determined daily during the course of the culture experiment. The results showed that at the lowest iron concentration (0.01 μM) the growth of M. viridis was seriously limited, and the maximal cell density was only approximately 6.4% of the density observed with an iron concentration of 18 μM. Iron availability dramatically affected chlorophyll a, carotenoid and phycocyanin content, with the greatest impact on chlorophyll a. The iron‐induced changes in content and ratios of pigments were detectable through spectral reflectance. Eleven spectral indices previously developed for the estimation of concentrations and/or ratios of pigments and a newly proposed chlorophyll a/phycocyanin index were found to be suitable for generating sensitive regression models between cellular iron content and spectral parameters. The comprehensive application of key sensitive spectral indices and regression equations should help to support monitoring and diagnosis of iron availability to cyanobacteria via remote sensing.     

西瓜八氢番茄红素合成酶基因片段的克隆和序列分析

以西瓜品种ZXG00152为材料,提取瓜瓤总RNA,进行反转录,依据植物八氢番茄红素合成酶(PSY)的氨基酸保守序列设计引物,以cDNA第一链为模板,扩增得到长约750 bp的cDNA片段。将该片段克隆到pMD19-T载体,测序结果表明该基因片段长748 bp,编码249个氨基酸,Blast搜索结果表明,由该片段推导出的氨基酸序列与其它植物的八氢番茄红素合成酶有较高的同源性,其中与甜瓜的一致性达到97.8%。该片段已在GenBank中登录(登录号:DQ494214)。     

The Arabidopsis Spontaneous Cell Death1 gene, encoding a ζ-carotene desaturase essential for carotenoid biosynthesis, is involved in chloroplast development,photoprotection and retrograde signalling

Carotenoids, a class of natural pigments found in all photosynthetic organisms, are involved in a variety of physiological processes, including coloration, photoprotection, biosynthesis of abscisic acid （ABA） and chloroplast biogenesis. Although carotenoid biosynthesis has been well studied biochemically, the genetic basis of the pathway is not well understood. Here, we report the characterization of two allelic Arabidopsis mutants, spontaneous cell death1-1 （spcl-1） and spc1-2. The weak allele spc1-1 mutant showed characteristics of bleached leaves, accumulation of superoxide and mosaic cell death. The strong mutant allele spc1-2 caused a complete arrest of plant growth and development shortly after germination, leading to a seedling-lethal phenotype. Genetic and molecular analyses indicated that SPC1 encodes a putative ζ-carotene desaturase （ZDS） in the carotenoid biosynthesis pathway. Analysis of carotenoids revealed that several major carotenoid compounds downstream of SPC 1/ZDS were substantially reduced in spc1-1, suggesting that SPC 1 is a functional ZDS. Consistent with the downregulated expression of CAO and PORB, the chlorophyll content was decreased in spc1-1 plants. In addition, expression of Lhcb1. 1, Lhcbl. 4 and RbcS was absent in spc1-2, suggesting the possible involvement of carotenoids in the plastid-to-nucleus retrograde signaling. The spc1-1 mutant also displays an ABA-deficient phenotype that can be partially rescued by the externally supplied phytohormone. These results suggest that SPC1/ZDS is essential for biosynthesis of carotenoids and plays a crucial role in plant growth and development.     

Dissecting the biosynthetic pathway for the bypass1 root-derived signal

The Arabidopsis BYPASS1 (BPS1) gene is required for normal root and shoot development. In bps1 mutants, grafting and root excision experiments have shown that mutant roots produce a transmissible signal that is capable of arresting shoot development. In addition, we previously showed that growth of bps1 mutants on the carotenoid biosynthesis inhibitor fluridone resulted in partial rescue of both leaf and root defects. These observations suggest that a single mobile carotenoid-derived signal affects both root and shoot development. Here, we describe further characterization of the bps1 root-derived signal using genetic and biosynthetic inhibitor approaches. We characterized leaf and root development in double mutants that combined the bps1 mutant with mutants that have known defects in genes encoding carotenoid processing enzymes or defects in responses to carotenoid-derived abscisic acid. Our studies indicate that the mobile signal is neither abscisic acid nor the MAX-dependent hormone that regulates shoot branching, and that production of the signal does not require the activity of any single carotenoid cleavage dioxygenase. In addition, our studies with CPTA, a lycopene cyclase inhibitor, show that signal production requires synthesis of beta-carotene and its derivatives. Furthermore, we show a direct requirement for carotenoids as signal precursors, as the GUN plastid-to-nucleus signaling pathway is not required for phenotypic rescue. Together, our results suggest that bps1 roots produce a novel mobile carotenoid-derived signaling compound.     

The reactivity of carotenoid radicals with oxygen

The possibility that carotenoid radicals react with oxygen to form chain-carrying peroxyl radicals has been postulated to account for the reduction in antioxidant effetiveness displayed by some carotenoids at high oxygen concentrations. The primary objective of the work described in this paper was to measure the rate constants for oxygen addition to a series of carotenoid radicals and to examine any influence of carotenoid structural features on these rate constants. Laser flash photolysis has been used to generate long-lived carotenoid radicals (PhS-CAR^√) derived from radical addition reactions with phenylthiyl radicals (PhS^√) in benzene. The PhS-CAR^√ radicals are scavenged by oxygen at rates that display a moderate dependence on the number of conjugated double bonds (n_db) in the carotenoid. The rate constants range from ∼10³ to ∼10⁴ M^- 1 s^- 1 for n_db = 7-11. The data also suggest that the presence of terminal cyclic groups may cause an increase in the rate constant for oxygen addition.     

黄秋葵八氢番茄红素脱氢酶基因的克隆与分析

该研究根据黄秋葵(Hibiscus esculentus L.)转录组测序获得的八氢番茄红素脱氢酶基因(HePDS)序列(GenBank登录号为MG372370)设计引物,克隆验证得到1条HePDS基因全长为2 020 bp cDNA,开放阅读框(ORF)包含1 686个碱基;预测其编码561个氨基酸,理论分子量为62.62 kD,等电点为8.155;编码的蛋白与海岛棉(Gossypium barbadense)、雷蒙德氏棉(Gossypium raimondii)、陆地棉(Gossypium hirsutum)同源蛋白的相似性均在93%以上,均含有1个保守的二核苷酸结合域和1个类胡萝卜素结合域,显示其高度的保守性。荧光定量PCR 分析表明,HePDS基因在黄秋葵根、茎、叶、花和果荚中均有表达;叶发育过程以嫩叶中表达最高,果实发育中以花后2 d表达量最高。类胡萝卜素含量随着叶、果实发育逐渐升高,成熟叶的含量最高,果实以花后4 d含量最高,且HePDS基因的表达与类胡萝卜素含量存在密切的相关性。该研究结果为进一步探讨HePDS基因的功能和调控机制,以及采用VIGS和CRISPR/Cas9技术开展黄秋葵基因功能的反向遗传学研究奠定了基础。