茉莉素介导的长春花生物碱次生代谢转录调控机制

萜类吲哚生物碱（terpeniod indole alkaloids, TIAs）是植物中产生的一类具有药理活性的次生代谢产物.药用植物长春花（Catharanthus roseus）因含有长春碱和长春新碱等重要的抗肿瘤萜类吲哚生物碱而成为研究TIAs次生代谢的主要模式植物.应用正、反向遗传学和各种代谢组学技术对长春花TIAs次生代谢途径及其调控进行了较深入的研究,相继鉴定了参与TIAs代谢途径调控的CrORCAs、CrMYCs、CrZCTs和CrWRKYs等转录因子,特别是发现茉莉素（jasmonates, JAs）介导TIAs生物合成的转录调控网络. 本文以长春花TIAs生物合成途径为模式,重点论述其代谢途径中的关键酶、参与调节的转录因子,尤其是茉莉素介导的调控网络及机制,解析植物中这些天然抗癌生物碱合成积累水平低的制约因素和组织细胞特异性,讨论基于这些新知识的长春花抗肿瘤TIAs代谢工程策略和工厂化绿色生产前景.     

茄属生物碱的研究进展

甾体生物碱(SA)主要是茄属植物体内的一种次级代谢产物。它复杂的结构多样性决定了生物活性的多样性。它的合成途径也比较复杂,尚不十分清楚。以生物碱类化合物的化学结构为基础,对近几年来茄属生物碱的研究现状进行了简要综述。主要论述了茄属生物碱的化学结构、含量分布、生理活性以及与茄属生物碱合成途径相关的分子生物学研究。并分析了茄属生物碱今后的发展方向。以期为以后研究糖苷生物碱的生物合成途径、毒性机制、药理学作用等奠定一定的基础。     

人肠道菌对天然产物代谢及转化的研究进展

天然产物的人肠道菌代谢及转化研究已引起各国学者的重视,并作为热点课题进行了大量研究工作。本文对近二十年来各国学者关于黄酮类、萜类、苯丙素类、生物碱类、甾体类及其他天然产物的人肠道菌代谢及转化研究工作进行了综述,总结了各类天然产物在人肠道菌作用下的代谢路径及转化规律,以期为该领域的进一步深入研究提供参考。     

miRNA调控药用植物生长发育和次生代谢

microRNA(miRNA)作为一类内源性的短链非编码RNA,广泛存在于真核细胞中,主要通过对转录本剪切和抑制翻译等方式,参与转录后基因的表达调控。近年来研究表明,多种药用植物中鉴定出大量的miRNA。这些miRNA对药用植物的生长发育和次生代谢产物合成具有调控功能。次生代谢产物是药用植物的主要有效成分,研究miRNA对药用植物次生代谢过程的调控作用具有十分重要的意义。本文综述了miRNA在植物中的产生途径、作用方式和体内功能,在此基础上重点介绍了miRNA对药用植物生长发育和次生代谢产物生物合成的调控作用,并对药用植物miRNA的研究进行了展望,以期为提高药用植物产量,高效获得药用植物有效成分以及临床应用开拓新的思路。     

猴头菌属药用真菌活性次级代谢产物研究概况

对猴头菌属药用真菌的次级代谢产物化学、生物活性研究进行了综述。目前已经从猴头菌属真菌中发现了83个不同类型的活性次级代谢产物,主要包含二萜类、酚类、脂肪酸类、甾体、生物碱类化合物;这些化学成分显示了抗肿瘤、抗菌、抗糖尿病、促进神经生长因子合成等多种活性。文中讨论了目前研究的主要问题并对其前景进行了展望。     

药用植物次生代谢工程研究概况

植物次生代谢工程,是通过基因工程技术改变植物体内的合成和代谢途径,以满足人类对天然植物次生代谢产物不断提高的需求。随着对药用植物次生代谢合成途径日渐全面的认识,采取有效的代谢工程策略对植物次生代谢途径进行遗传改良,已经取得了诸多研究成果。但是,对代谢途径的总体调控以及次生代谢途径之间的协调等方面,仍然了解甚少,而利用系统生物学方法开展预见性代谢工程将会成为未来的研究趋势。     

微生物异源合成植物异喹啉生物碱的新进展

植物异喹啉生物碱(plant isoquinoline alkaloids,PIAs)包括吗啡、可待因、加兰他敏及小糵碱等药用活性产物和其他天然活性产物。从植物中提取异喹啉生物碱,受制于低含量、种植季节及提取方法。人们开始研究利用微生物异源合成和改造天然异喹啉生物碱,从而获得低成本的药用活性物质。异喹啉生物碱合成途径长,反应复杂,为实现微生物异源合成带来了诸多挑战。随着合成途径和酶的解析和鉴定,合成生物学技术为在微生物中合成异喹啉生物碱提供了可能。综述了PIAs合成途径解析的最新进展,以及微生物异源合成PIAs的代谢工程策略,讨论了目前存在的问题和未来的发展趋势。     

糖苷生物碱化学生态学研究进展

糖苷生物碱(glycoalkaloid)是主要分布于茄科和百合科植物中的糖苷类次级代谢产物,糖链通常由3或4个单糖组成,苷元通常为三类甾体生物碱:茄次碱烷、螺旋甾碱烷和其他甾体衍生物.糖苷生物碱的主要生物学功能是化学防御,具有阻止昆虫取食、抑制微生物、化感作用和协同进化等重要作用.本文在阐明糖苷生物碱的来源和化学结构的基础上,着重总结了糖苷生物碱化学生态学研究的现状、进展及其生物学意义,分析了今后的发展方向.     

异喹啉类生物碱生物合成、运输、储藏相关细胞生物学研究进展

生物碱是存在于自然界中一类含氮的杂环小分子天然化合物, 约有1.2万多种。其代谢途径往往受到特异酶类的调控, 因此通过对某些特征性关键酶的定位可以确定生物碱的合成、转运和储藏相关的特定细胞或亚细胞结构。该文以异喹啉类生物碱血根碱为主, 对其生物合成、运输和储藏相关的细胞和亚细胞水平上的研究结果进行概述。异喹啉生物碱生物合成主要发生在皮层、筛管、伴胞和乳汁管等组织细胞中, 囊泡、液泡、细胞质基质、微粒体、内质网和叶绿体类囊体等众多细胞器参与生物碱的运输和储存。同时对药用植物中常见的其它几类主要生物碱的相关研究结果进行了讨论。     

长春花萜类吲哚生物碱的生物合成途径

药用植物长春花含有130余种萜类吲哚生物碱,该文对近年来国内外有关长春花生物碱合成的上游和下游阶段及其相关研究进行详细的归纳总结。长春花上游合成途径中在相应的酶促作用下由吲哚途径产生的色胺和由类萜途径产生的裂环马钱子苷在异胡豆苷合成酶的催化作用下形成了所有长春花TIAs的共同前体物质3α-异胡豆苷,3α-异胡豆苷再由下游途径的各种酶促作用下生成种类各异的长春花TIAs。通过对长春花TIAs合成途径的阐述,为萜类吲哚生物碱合成及其代谢调控的相关研究提供参考。     

Steroidal glycoalkaloids in cell and shoot teratoma cultures ofSolanum dulcamara

Bittersweet (Solanum dulcamara L., Solanaceae) is of interest as a source of steroidal alkaloids for the commercial production of hormones. Since glycoalkaloid production is positively correlated to differentiation, tumor and teratoma cultures of the soladulcidine chemotype were established by transformation withAgrobacterium tumefaciens. A newly developed HPLC-system, which allowed separation and sensitive quantitation of the glycoalkaloids soladulcidine-tetraoside, solamargine and solasonine, was used to analyse glycoalkaloid profiles in plants and cultures. Tumors and teratoma were charcterized by a shift in their alkaloid pattern from soladulcidine tetraoside to the solasodine glycosides solamargine and solasonine. Shoot teratoma showed a total glycoalkaloid content of 1% dw, which is about fivefold higher than in the source plant. A regenerated plant retained the altered alkaloid spectrum; the levels, however, equalled those of the source plant. From the alteration of alkaloid pattern in the transformed cultures suggestions can be made concerning the biosynthetic pathway. Completion of the biosynthesis of the aglycone is likely to be complete before glycosylation occurs.     

The steroidal glycoalkaloid α-tomatine

The literature relating to chemical, biochemical and biological aspects of the steroidal glycoalkaloid, α-tomatine, is reviewed. The alkaloid, which can be used as a starting compound for the synthesis of steroidal hormones, is toxic to a wide range of living organisms. The significance of tomatine to plants which elaborate it is discussed and some possible uses of the compound are mentioned.     

Metabolic and functional diversity of saponins,biosynthetic intermediates and semi-synthetic derivatives

Abstract

Saponins are widely distributed plant natural products with vast structural and functional diversity. They are typically composed of a hydrophobic aglycone, which is extensively decorated with functional groups prior to the addition of hydrophilic sugar moieties, to result in surface-active amphipathic compounds. The saponins are broadly classified as triterpenoids, steroids or steroidal glycoalkaloids, based on the aglycone structure from which they are derived. The saponins and their biosynthetic intermediates display a variety of biological activities of interest to the pharmaceutical, cosmetic and food sectors. Although their relevance in industrial applications has long been recognized, their role in plants is underexplored. Recent research on modulating native pathway flux in saponin biosynthesis has demonstrated the roles of saponins and their biosynthetic intermediates in plant growth and development. Here, we review the literature on the effects of these molecules on plant physiology, which collectively implicate them in plant primary processes. The industrial uses and potential of saponins are discussed with respect to structure and activity, highlighting the undoubted value of these molecules as therapeutics.     

Synthesis and trafficking of alkaloid biosynthetic enzymes

The biosynthesis of plant natural products involves a large number of enzymes that create and elaborate a bewildering array of chemical structures, which are generally involved in ecophysiological interactions. Alkaloids are one of the largest groups of natural products and are generally produced through an assortment of intricate pathways. The application of molecular biochemical approaches to investigate the cell biology of alkaloid pathways has revealed a paradigm for the complex, yet highly ordered, organization of biosynthetic enzymes at both the cellular and subcellular levels. Many different cell types have been implicated in alkaloid formation and storage, in one case suggesting the intercellular transport of enzymes. The localization of enzymes to numerous cellular compartments shows the importance of protein targeting in the assembly of alkaloid pathways. Recent studies have also pointed to the possible interaction of biosynthetic enzymes in multi-enzyme complexes. These processes must be considered to be integral components of the mechanisms that regulate alkaloid biosynthesis and perhaps other natural product pathways.     

The structure of Rauvolfia serpentina strictosidine synthase is a novel six-bladed beta-propeller fold in plant proteins

The enzyme strictosidine synthase (STR1) from the Indian medicinal plant Rauvolfia serpentina is of primary importance for the biosynthetic pathway of the indole alkaloid ajmaline. Moreover, STR1 initiates all biosynthetic pathways leading to the entire monoterpenoid indole alkaloid family representing an enormous structural variety of approximately 2000 compounds in higher plants. The crystal structures of STR1 in complex with its natural substrates tryptamine and secologanin provide structural understanding of the observed substrate preference and identify residues lining the active site surface that contact the substrates. STR1 catalyzes a Pictet-Spengler-type reaction and represents a novel six-bladed beta-propeller fold in plant proteins. Structure-based sequence alignment revealed a common repetitive sequence motif (three hydrophobic residues are followed by a small residue and a hydrophilic residue), indicating a possible evolutionary relationship between STR1 and several sequence-unrelated six-bladed beta-propeller structures. Structural analysis and site-directed mutagenesis experiments demonstrate the essential role of Glu-309 in catalysis. The data will aid in deciphering the details of the reaction mechanism of STR1 as well as other members of this enzyme family.     

Seasonal variation in toxic steroidal alkaloids of foothill death camas (Zigadenus paniculatus)

Death camas (Zigadenus spp.) is a common poisonous plant in North America with plants occurring in a wide variety of habitats with species of toxic concern occurring primarily in meadows, grasslands, shrublands, and mountains. The toxicity of Zigadenus species has been attributed to a series of steroidal alkaloids. The objective of this study was to evaluate zygacine and total steroidal alkaloid concentrations in different plant tissues of Zigadenus paniculatus as a function of plant maturity. Death camas plants were collected at two locations at different developmental growth stages representing vegetative, flower, seed pod, and shattered seed pod stages. Zygacine represented greater than 50% of the total steroidal alkaloids at all developmental stages. In bulbs, total steroidal alkaloid and zygacine concentrations did not change significantly as a function of plant phenology, and concentrations were lower than what were observed in above ground plant parts. Total steroidal alkaloid and zygacine concentrations in above ground parts were highest at early vegetative growth stages and decreased over the growing season. In plant reproductive parts, total steroidal alkaloid and zygacine concentrations increased until maturity and then decreased as the plant senesced. The concentrations of steroidal alkaloids reported here suggest that the toxic risk associated with death camas is greatest in the early vegetative growth stages followed by the flower and pod stages. There is a toxic risk to livestock as long as the plant is present, and caution should be taken when grazing livestock in areas with death camas until the plant senesces.     

Transformation of opium poppy (<Emphasis Type="Italic">Papaver somniferum</Emphasis>L.) with antisense berberine bridge enzyme gene (<Emphasis Type="Italic">anti-bbe</Emphasis>) via somatic embryogenesis results in an altered ratio of alkaloids in latex but not in roots

The berberine bridge enzyme cDNA bbe from Papaver somniferumL. was transformed in antisense orientation into seedling explants of the industrial elite line C048-6-14-64. In this way, 84 phenotypically normal T₀ plants derived from embryogenic callus cultures were produced. The selfed progeny of these 84 plants yielded several T₁ plants with an altered alkaloid profile. One of these plants T₁-47, and its siblings T₂-1.2 and T₂-1.5 are the subject of the present work. The transformation of these plants was evaluated by PCR, and northern and Southern hybridisation. The transgenic plants contained one additional copy of the transgene. The alkaloid content in latex and roots was determined with HPLC and LC-MS. We observed an increased concentration of several pathway intermediates from all biosynthetic branches, e.g., reticuline, laudanine, laudanosine, dehydroreticuline, salutaridine and (S)-scoulerine. The transformation altered the ratio of morphinan and tetrahydrobenzylisoquinoline alkaloids in latex but not the benzophenanthridine alkaloids in roots. The altered alkaloid profile is heritable at least to the T₂ generation. These results are the first example of metabolic engineering of the alkaloid pathways in opium poppy and, to our knowledge, the first time that an alkaloid biosynthetic gene has been transformed into the native species, followed by regeneration into a mature plant to enable analyses of the effect of the transgene on metabolism over several generations.