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Specialized Metabolism in Plant Glandular Trichomes

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Abstract

腺毛(trichome)是广泛存在植物表面的一种形态各异的特化组织。一些类型的腺毛称为腺体腺毛(Glandular trichome),能够特异的大量合成种类繁多的次生代谢物质。这些次生代谢物质对于植物适应外界生物和非生物胁迫具有重要的作用,同时对于我们人类生活生产也具有很重要的价值。根据代谢物的结构和合成路径,主要将腺体腺毛产生的代谢产物分为萜类(terpenoids)、苯丙素类(phenylpropanoids)、生物碱类(alkaoids)、酰基糖类(acyl sugars)、甲基酮类(methylketones)、黄酮类(flavonoids)以及一些脂肪酸和氨基酸的衍生物。由于腺体腺毛和其代谢物易于收集和分析,因此参与这些代谢物合成的基因和蛋白已经有大量详细的研究。本综述拟对上述物质的合成过程、生物功能以及相应的植物物种进行一个简单的描述。
中国科学: 生命科学 2015 45 6: 557 ~ 568
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引用格式: 李好勋, 王国栋. 植物腺毛次生代谢产物生物合成的研究进展. 中国科学: 生命科学, 2015, 45: 557–568
Li H X, Wang G D. Specialized metabolism in plant glandular trichomes. SCIENTIA SINICA Vitae, 2015, 45: 557–568, doi: 10.1360/N052015-00073
中国科学杂志社
SCIENCE CHINA PRESS
中国知名大学与研究所专栏 中国科学院遗传与发育生物学研究所专题
植物腺毛次生代谢产物生物合成的研究进展
李好勋, 王国栋*
中国科学院遗传与发育生物学研究所, 北京 100101
* 联系人, E-mail: gdwang@genetics.ac.cn
收稿日期: 2015-03-05; 接受日期: 2015-04-15; 网络版发表日期: 2015-05-25
国家重点基础研究发展计划(批准号: 2013CB127000)资助项目
doi: 10.1360/N052015-00073
摘要 植物表皮毛(trichomes)是广泛存在于高等植物表面的一种特化器官, 尽管形态各异,
但通常可被分成腺毛(glandular trichomes)和非腺毛(non-glandular trichomes) 2 大类. 其中腺毛
的一个重要特征是特异地大量合成种类繁多的次生代谢产物. 这些次生代谢产物不仅对植物
适应外界生物和非生物胁迫具有重要的作用, 同时对人类的生产生活也具有很重要的经济价
. 近年来随着各种组学技术的飞速发展, 人们对参与这些代谢物生物合成的基因及其调控
机理已经有较为详细的认识. 本文拟对植物腺毛中次生代谢产物的生物合成过程、调控机制
以及其合成生物学应用等方面的进展做一简要综述.
关键词
腺毛
次生代谢
组学技术
合成生物学
植物表皮毛是陆生植物表面(叶片或茎秆上)
见的组织, 可被分成腺毛和非腺毛 2大类(1C).
腺毛由于不具有合成和积累大量次生代谢产物的能
, 所以在本文中不加赘述. 腺毛通常由多细胞构成,
在结构上可分为基部细胞(basal cells)支持细胞(stalk
cells)和顶端细胞(apical cells) 3 个部分. 据统计大约
30%维管植物的地上部分(茎杆或叶子的表面)有腺毛
存在, 有时在同一植物上可以发现几种不同类型的
腺毛, 如番茄(Solanum lycopersicum)的表面存在 4
腺毛, 分别为Ⅰ, , Ⅵ和Ⅶ类型[1](1A). 腺毛被
认为是植物在长期进化过程中对生态环境适应的结
, 对植物适应外界生态环境具有重要作用(如抵御
食草动物的啃食和病原菌的入侵以及参与非生物胁
迫应答等). 腺毛的一个非常显著特征是具有很强的
合成、储存或分泌大量次生代谢产物的能力. 同时,
腺毛结构简单, 相对容易分离提取: 玻璃珠-滤网过
(glass bead-mesh filter)是常用的分离富集方法;
于镶嵌在植物叶表面的腺毛, 目前常利用激光显微
切割技术(laser microdissection, LMD)进行分离、富
. 所以, 腺毛为研究植物次生代谢产物合成途径及
调控提供了一个很好的平台. 许多腺毛合成的植物
天然产物具有很重要的商业价值, 它们作为制药前
体、香精香料、食品添加剂以及天然杀虫剂等被广泛
应用[2,3]. 因此, 腺毛有植物化学工厂的美誉, 越来
越多的从事植物化学、植物次生代谢及生物技术的研
究人员开始涉足这一领域, 详细研究腺毛中这些具
有高附加值的植物天然产物代谢及其调控[4]. 之前关
于腺毛的代谢途径研究多集中于唇形科的香料植物
如薄荷(Mentha piperita)和罗勒(Ocimum basil-
icum)[5~8], 现在已经扩展到菊科植物青蒿(Artemisia
annua)向日葵(Helianthus annuus)和除虫菊(Chrysan-
themum cinerariaefolium), 茄科植物烟草(Nicotiana
李好勋等: 植物腺毛次生代谢产物生物合成的研究进展
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1 不同形态的植物腺毛及它们富含的代谢物类型
A: 番茄腺毛(主要是Ⅵ类型), 富含萜类、甲基酮、酰基糖苷等; B: 大麻腺毛, 富含四氢大麻酚等物质; C: 苜蓿腺毛(a: 腺毛; b: 非腺毛),
富含脂肪酰胺类物质; D: 啤酒花腺毛, 富含萜类、黄腐醇和苦味酸; E: 青蒿腺毛, 富含青蒿素等萜类物质
tabacum)和番茄, 豆科植物蒺藜苜蓿(Medicago
truncatula)和紫花苜蓿(Medicago sativa), 大麻科植
物大麻(Cannabis sativa)和啤酒花(Humulus lupulus)
[9~17].
1 植物腺毛次生代谢研究的系统学方法
由于腺毛位于植物体表面, 其组织结构不和维
管束系统相连接, 而且腺毛部分通常不能进行光合
作用[18](许多物种腺毛的转录组数据分析都支持这一
论点). 因此, 腺毛中物质合成所需的能量和起始小
分子前体物质都来源于初级代谢产物, 如氨基酸、
肪酸和糖酵解产物等. 初级代谢提供能量的多少和
前体物质的种类和数量, 从某种程度上直接决定了
腺毛中次生代谢产物的合成种类和合成量. 随着测
序技术和各种组学技术的飞速发展, 腺毛次生代
谢的研究也从最初的小规模表达序列标签(expressed
sequence tags, EST)测序(结合相关酶的纯化)和单
个基因的功能鉴定逐步走向大规模测序, 比较基
因组学研究和代谢网络构建. 目前策略通常是以
趣化合物”(metabolites of interest)含量很高的腺毛和
其他组织作为起始材料获得代谢组学、蛋白质组学和
转录组学数据(腺毛数据库相关网站: http://www.
planttrichome.org http://bioinfo.bch.msu.edu/
trichome_est), 然后对不同类型的大量数据进行生物
信息学关联分析, 从宏观和微观 2个层面对兴趣化
合物的代谢途径及调控进行系统的功能分析和应用
研究[19](2). 这种研究方法对非模式植物(许多次生
代谢研究的植物物种目前都没有完整的基因组序列
2 系统解析植物腺毛化学工厂及其合成生物学重构
在这一过程中候选基因的生理化功能验证是连接组学数据关联
分析产生假说和代谢物合成生物学应用的关键环节, 这是一个不断
优化和改进的过程, 以最终达到产业化的目的
信息)非常有效, 已有许多成功应用的报道[1,20~22].
要指出, 尽管利用这些方法已经鉴定出许多功能基
, 但参与腺毛发育、代谢调控的基因到目前为止仍
只有零星的报道[23,24], 造成这一问题的主要原因是
这些非模式植物还没有成熟的转化体系.
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2 腺毛中代谢途径的研究进展
根据腺毛中次生代谢产物合成的前体物质来源
以及这些次生代谢产物的结构特征, 主要将这些次
生代谢产物分为萜类(terpenoid)、苯丙素类(pheny-
lpropanoid)和聚酮类化合物(polyketides)酰基糖苷类
(acyl sugars) 以及脂肪酸的衍生物(fatty acids
derivatives)(3).
2.1 萜类
萜类是种类和数目最多的一类植物次生代谢产
, 它也广泛存在于植物腺毛中, 迄今已有近 5万多
个萜类分子及其衍生物的结构被解析[25]. 萜类物质
的骨架来源相对简单, 都是由基本的 C5 单元异戊烯
二磷酸(isopentenyl diphosphate, IPP)和二甲烯丙基二
磷酸(dimethylallyl diphosphate, DMAPP)聚合形成[26].
根据所含 C5 单元数目的不同, 萜类可分为半萜
(hemiterpene, C5)、单萜(monoterpene, C10)、倍半萜
(sesquiterpene, C15)和二萜(diterpene, C20). 在植
物体内有 2条路径合成 C5 单元, 分别为 MEP
(methylerythritol phosphate)途径和 MVA(mevalonic
acid)途径. 目前认为 MEP 途径完全定位于质体中[27],
MVA 途径可能分布在胞质、内质网和过氧化物酶
体中[28]. MEP 途径能够合成 IPP DMAPP, MVA
径仅可以合成 IPP, 但植物多个细胞器中都存在催化
IPP 转化为 DMAPP 的异戊烯基焦磷酸异构酶(isopen-
tenyl diphosphate isomerase, IDI)[29,30]. 在短链异戊烯
基转移酶的催化作用下, IPP DMAPP 可以聚合形
成牻牛儿基焦磷酸(geranyl diphosphate, GPP)橙花基
焦磷酸(neryl diphosphate, NPP) 、菊酰焦磷酸
(chrysanthemyl diphosphate)、法呢基焦磷酸(farnesyl
diphosphate, FPP)和牻牛儿牻牛儿基焦磷酸(geranyl-
geranyl diphosphate, GGPP), 这些基本前体物质在
萜类合成酶或环化酶催化下生成种类繁多的萜类骨
, 通常这些萜类骨架会在不同修饰酶的作用下
生成结构更为复杂的萜类终产物. 目前已有的实验
证据表明在植物腺毛中 MEP 途径通常是提供萜类物
质生物合成(无论是单萜还是倍半萜)前体的唯一来
[31].
目前许多腺毛中的萜类合成途径已经得到深入
研究. 其中美国华盛顿州立大学的 Croteau 课题
[32~34]在对薄荷腺毛次生代谢方面的研究做了许多
开创性的工作. 薄荷的腺毛大量积累萜类物质,
Croteau 课题组结合传统的酶蛋白纯化和小规模 EST
数据分析的方法, 已经功能鉴出中单萜薄荷烷(p-
menthane)合成路径的几乎全部基因, 包括异源二聚
体的 GPPS、柠檬烯环化酶、下游修饰基因如 P450
和脱氢酶等. 唇形科紫苏属的一些物种的腺毛中能
够大量富集不同类型的单萜, 参与这些单萜合成的
基因如催化柠檬精油、月桂烯、香叶醇和沉香醇合成
3 本文提及的各种植物腺毛来源的代表性化合物
李好勋等: 植物腺毛次生代谢产物生物合成的研究进展
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的合成酶基因已经被发现和鉴定[35~37]. 罗勒腺毛中
也合成大量的萜类, 如牻牛儿醇(geraniol) 、芳樟醇
(linalool), 目前已发现多个萜类合成酶参与这些萜
类的合成[7,38,39]. 天竺薄荷(Pogostemon cablin)的腺毛
中积累超过 20 种倍半萜, 其中已经克隆到 5个参与
这些倍半萜合成的基因[40].
茄科茄属大部分物种(如番茄和烟草)的叶片上
都存在合成萜类的腺毛. 美国密歇根大学 Pichersky
课题组[15,41,42]在番茄的腺毛中发现一系列参与单萜
合成的基因, 包括一个短萜类合成的顺式异戊烯基
转移酶 NDPS1(neryl diphosphate synthase 1)和一个参
与单萜
-水芹烯(-phellandrene)合成的萜类合成酶
PHS1(phellandrene synthase 1). 最近 Pichersky 课题
[43,44]又从进化的角度和基因组结构层面对番茄中
-水芹烯代谢途径进行了详尽阐述. 烟草腺毛能够
积累二萜 Cembradiol, 通过反向遗传学的方法已经克
隆得到参与 Cembradiol 生物合成的合成酶和催化骨
架修饰步骤的单加氧酶[45].
倍半萜内酯是菊科植物特有的一类次生代谢产
. 其中青蒿素是菊科植物黄花蒿(Artemisia annua)
腺毛中合成的一种倍半萜内酯, 由于其具有高抗疟
疾的药理功效而被广泛使用. 青蒿素市场需求大,
关研究报道较多, 而且在近期多篇综述中也有提
[46,47], 在这里不做赘述. 最近, 英国 Graham 及其
同事[48]对青蒿的转录组进行了深度测序, 结合常规
育种群体, 他们找到了控制青蒿素产量的关键基因
位点, 并绘制了首张青蒿素的数量性状遗传图谱,
一遗传图谱为将来利用育种技术提高青蒿素产量提
供了知识储备. 另一菊科植物除虫菊(Chrysanthem-
um cinerariifolium), 位于其子房上的腺毛除合成除
虫菊酯(Pyrethrin, 一种由不规则单萜酸和 lipoxy-
genases 途径生成的醇聚合形成的酯, 是一种常用的
广谱杀虫剂), 还生成一些倍半萜内酯类的化合物,
最近这 2类化合物生物合成途径也得到了比较全面
的功能解析[13,49,50].
随着各种化学分析技术的发展, 人们从自然界
发现了越来越多的新的萜类骨架. 例如, 中国科学院
昆明植物研究所的黎胜红课题组[51]的研究表明分布
于我国云南的唇形科大型木本植物米团花(Leucosce-
ptrum canum)的腺毛中能够合成和储存一类罕见的二
倍半萜化合物 Leucosceptroids A Leucosceptroids B,
对植食性昆虫具有较强的拒食活性, 并对植物病原
菌具有明显的抑制活性, 且该类化合物在米团花叶
和腺毛中的含量与它们的拒食中浓度相当或更高,
足以抵御植食性昆虫的取食, 表明二倍半萜在米团
花中具有明显的防御植食性昆虫和植物病原菌的功
. 该课题组进一步的化学分析发现, Leuco-
sceptroids A Leucosceptroids B , 米团花的叶和
花中还含有一系列(60 )结构高度变化的二倍半
萜或降二倍半萜化合物(统称米团花烷二倍半
)[52~54]. 但目前人们对参与这些化合物生物合成途
径的基因还知之甚少, 无论从基础科研角度还是应
用的角度, 对这类二倍半萜物质生物合成途径的研
究都很值得期待.
2.2 苯丙素类
苯丙素类和萜类一样是植物腺毛中合成的重要
次生代谢产物, 也是一些唇形科植物腺毛精油的主
要成分. 苯丙素类物质同样具有结构的多样性, 不同
物种的腺毛通常积累不同的苯丙素类物质[55,56].
然结构上存在差异, 但苯丙素类物质合成都始于苯
丙氨酸. 苯丙氨酸经苯丙氨酸裂解酶、肉桂酸羟化
酶和香豆酸辅酶 A 连接酶 3步顺序催化反应生成大
多数苯丙素类物质合成的前体结构 4-羟肉桂酰辅
A[55,57]. 在罗勒的盾状腺毛中, 通过苯丙素合成路
, 能够在腺毛中合成和积累丁香油酚(eugenol)、萎
叶酚(chavicol)以及 2种物质的甲基化衍生物[58].
, 还没有发现参与丁香油酚和萎叶酚的前体物松
柏醇(coniferyl alcohol)的合成酶. 松柏醇在松柏醇乙
酰基转移酶的催化下转变为乙酸松柏酯, 进一步在
丁香油酚合成酶或萎叶酚合成酶的催化下合成丁香
油酚或萎叶酚[59]. 通常, 丁香油酚和萎叶酚进一步被
甲基化, 形成相应的甲基衍生物[60]. 关于苯丙素类物
质的具体生物功能还不清楚, 目前认为一些苯丙素
类物质参与植物的防御反应, 如前面提到的丁香油
酚具有较强的防腐和抗真菌效果; 同时研究也发现
一些苯丙素类物质是花香的构成成分, 人们由此猜
测这些化合物可能在植物-昆虫授粉的过程中发挥作
[61,62].
2.3 聚酮化合物
黄酮是一类广泛存在的具有多种生物学功能的
聚酮类化合物. 黄酮类物质合成前体 4-羟肉桂酰辅
A 来源于苯丙素代谢途径, 在查尔酮合成酶的催化
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作用下, 1 分子的 4-羟肉桂酰辅酶 A3分子的丙二
酰辅酶 A 聚合形成所有黄酮类物质的前体物柚皮素
查尔酮(naringenin chalcone). 然后, 在不同物种中和
不同类型酶的催化下形成各种不同类型的黄酮类物
, 包括黄酮、黄酮醇、黄烷双醇、花青素、原花青
素和类黄酮等[63,64]. 在腺毛中合成的黄酮类物质具
有多种生物学功能, 主要包括防御紫外线的辐射、
御微生物的入侵和食草动物的啃食等. 例如, 过量太
阳光照射下, 红景天(Phillyrea latifolia)的腺毛和叶片
能够合成和分泌黄酮苷, 以抵御光线的辐射[65,66];
茄的腺毛能够合成多种黄酮类物质, 包括甲基杨梅
酮、芸香苷、山柰素等, 这些物质具有抑制鳞翅目昆
虫幼虫生长的功效[67~69].
在腺毛中, 还存在其他聚酮类物质的合成. 例如,
在大麻科植物大麻(Cannabis sativa)的腺毛中能够合
成和积累异戊烯基化的聚酮类物质大麻素(can-
nabinoids). 临床研究表明大麻素具有重要的药理功
. 其生物合成途径已经基本研究清楚, 在聚酮合成
(tetraketide synthase, TKS)的催化作用下, 1 分子的
己酰辅酶 A(hexanoyl-CoA)3分子的丙二酰辅酶 A
聚合形成戊基二羟基苯酸(olivetolic acid), 进一步在
异戊烯转移酶的催化作用下形成大麻萜酚酸
(cannabigerolic acid), 然后经氧化、环化形成不同类
型的大麻素[70,71]. 体外生化分析表明, 聚酮合成酶催
化的反应通常会形成许多副产物, 例如, 大麻 TKS
在利用己酰辅酶 A(hexanoyl-CoA)和丙二酰辅酶 A
底物时其主要酶促产物为吡喃酮类副产物, 而不是
戊基二羟基苯酸. 加拿大 Page 课题组[72]最近发现大
TKS 需要戊基二羟基苯酸环化酶的协助(olivetolic
acid cyclase, OAC; 该酶自身没有酶学活性)才能催化
形成正确的产物戊基二羟基苯酸, 有趣的是这 2个蛋
白并不相互作用, 不能形成蛋白复合体. 在大麻科植
物啤酒花雌花腺毛中除能够积累大量萜类外, 还能
够积累异戊烯基化的聚酮类物质黄腐醇和苦味酸,
这些化合物赋予啤酒特殊的风味品质, 同时对于人
类健康也具有重要作用. 黄腐醇的合成由查尔酮合
成酶(chalcone synthase)催化 1分子的肉桂酰辅酶
A(p-coumaroyl- CoA)3个分子的丙二酰辅酶 A
合形成柚皮素查尔酮(naringenin chalcone), 后者进一
步被异戊烯基化和甲基化形成黄腐醇[12,73]. 苦味酸
的合成路径类似于黄腐醇, 在苯戊酮合成酶的催化
, 1 分子的短侧链酯酰辅酶 A3分子的丙二酰辅
A聚合形成苦味酸前提物, 进一步经异戊烯基化
和氧化形成终产物苦味酸[74~76]. 最近本课题组[77]
啤酒花中苦味酸代谢上游的各种辅酶 A前体物质的
生成进行了详细研究, 发现在啤酒花腺毛中, 定位于
线粒体的硫酯水解酶(HlTE4)和定位于胞质的脂酰辅
A连接酶(HlCCL2 HlCCL4)是连接支链氨基酸
降解和苦味酸生物合成的关键因素. 在此基础上本
课题组进一步功能鉴定了参与苦味酸合成的异戊烯
基转移酶 HlPT1L HlPT2, 发现 HlPT1L HlPT2
能够相互作用, 形成异源二聚体催化
-苦味酸生物
合成途径中连续 3步的异戊烯基化反应: HlPT1L
化第 1步异戊烯基化反应, HlPT2 负责第 2和第 3
步异戊烯基化反应[78]. 同时证明利用酿酒酵母
(Saccharomyces cerevisiae)系统生成啤酒花苦味酸是
可行的, 相关合成生物学的优化工作正在进行中.
2.4 脂肪酸衍生物
甲基酮类是饱和脂肪酸衍生形成的一类挥发性
的次生代谢产物[79]. 通常, 在植物中发现的甲基酮类
物质碳链长度为 7~15 个碳原子. 目前, 已在番茄中
发现多种甲基酮类物质, 包括 2-庚酮、2-壬酮、甲基
正辛基酮、十三烷酮和 2-十五烷酮等[10]. 多毛番茄
(Lycopersicon hirsutum subsp. glabratum)的Ⅵ型腺
毛能够大量合成多种甲基酮类物质, 总含量可达
叶片鲜重的 8%[10]. 研究表明, 甲基酮类物质的合
成前体来源于叶绿体中饱和脂肪酸合成的中间体 3-
ketoacyl-acyl 载体蛋白或过氧化物酶体中饱和脂肪降
解形成的 3- 酮脂酰辅酶 A(3-ketoacyl-CoAs). 3-
ketoacyl-acyl 载体蛋白和 3-酮脂酰辅酶 A在甲基酮合
成酶 2(methyl ketone synthase 2)的催化下水解形成 3-
酮酸(3-ketoacids), 后者进一步在甲基酮合成酶 1
化下脱羧形成甲基酮类物质[10,80]. 甲基酮类物质具
有高效的抗虫功效, 如十三烷酮对一些食草节肢动
(如对防治烟草天蛾幼虫(Manduca sexta)和棉花蚜
(Aphis gossypii))非常有效[81]; 多毛番茄的挥发性
分泌物和提取的十三烷酮能够杀死番茄螟蛉
(Helicoverpa zea)[82]; 此外, 甲基酮类物质对二斑叶
螨同样具有高效的毒害作用[83].
2.5 酰基糖苷类
酰基糖苷类物质是酯酰基团(短链和短侧链为主)
与糖类的羟基酯化形成的化合物, 在多数茄科植物
李好勋等: 植物腺毛次生代谢产物生物合成的研究进展
562
的腺毛中都有酰基糖苷类物质的合成与储存. 在野
生番茄(Solanum pennellii), 分泌在其叶表面的酰
基糖苷类物质可以占叶干重的 20%, 酰基糖苷类物
质主要由 2,3,4-O-三酰基葡萄糖、3,3,4-O-三酰基蔗
糖和 3,3,4,6-O-四酰基蔗糖构成[14,84]. 酰基糖苷类物
质除了对植食性昆虫有直接的毒害作用外, 最近的
研究表明这类化合物还参与植物的间接防御: 甜菜
夜蛾(beet armyworm)、烟草天蛾(tobacco hornworm)
非洲斜纹夜蛾(African cotton leafworm)3 种鳞翅目植
食性昆虫的幼虫会优先取食富含酰基糖苷类物质的
烟草叶片腺毛, 酰基糖苷类物质本身对这 3种植食性
昆虫幼虫的取食及发育没有不良影响, 但这些酰基
糖苷类物在幼虫的体内消化后在其粪便中会释放挥
发性的短侧链脂肪酸, 这种味道会吸引这 3种植食性
昆虫幼虫的一种天敌
杂食性的石竹蚁(Pogonom-
yrmex rugosus)[85]. 酰基糖苷类物质的生物合成途径
在番茄和烟草中研究得最为清晰, 通常认为酰基糖
苷类骨架中的糖分子来源于葡萄糖或蔗糖, 而酯酰
基团则来源于氨基酸降解后形成的短侧链或短直链
饱和脂肪酸, 经进一步链的延长, 通常为碳原子数目
2~12 的支链或直链脂肪酸[86,87]. 在茄属和曼陀罗
属物种中, 饱和脂肪酸合成路径介导酯酰侧链的延
; 而在烟草和矮牵牛花(Petunia hybrida), 酯酰
侧链通过
-ketoacid 介导延长[88]. 在多步酰基化反应
, 葡萄糖基转移酶(glucosyltransferase)催化酰基类
合成的第 1步乙酰化反应, 然后其产物作为酰基转移
酶的底物进一步被酰基化[89,90]. 最近, Schilmiller
[14] 在栽培番茄中发现一个 BAHD 酰基转移酶
(SlAT2), 识别三酰基蔗糖和乙酰辅酶 A 为底物,
化四酰基蔗糖的合成. 组织特异性分析表明, SlAT2
特异性地在番茄Ⅳ型腺毛的顶端细胞表达, 这与四
酰基蔗糖的合成部位相一致.
3 植物腺毛次生代谢研究与合成生物学应用
对人类而言, 很多植物次生代谢产物具有治疗
疾病的功效, 如前面提到的治疗疟疾的特效药青蒿
素等. 迄今为止, 植物次生代谢产物依然是探寻新药
的重要方向之一[91]. 但通常由于兴趣化合物结构
复杂, 人工化学合成成本高, 所以通过以大肠杆菌
(Escherichia coli)和酵母菌等微生物为载体的代谢工
(有时会也选用植物为载体, 但植物生长周期长、
传背景复杂、分子操作困难且效果难以预测), 选择性
的提高生物反应器中相关兴趣化合物的合成效
, 对满足人类需求具有重要的现实意义. 生物学技
术手段被引入代谢工程, 成为当下的研究热点[92],
别是在生物能源研究领域, 在取得一系列技术突破
的基础上 LS9 公司已经开始利用微生物进行商业化
生产生物燃料[93,94]. 合成生物学致力于工程化地组
装全新的生物学系统, 合成生物学/代谢工程结合强
调人工设计和构建核心生物学模块, 然后利用这些
标准化的生物学模块优化组合来建立人工生物体系,
使生物体能按预想的方式完成各种兴趣化合物
合成(宿主生物体自身原来没有这种能力)[95]. 当然,
合成生物学/代谢工程设计成功的前提是要对不同来
兴趣化合物的生物合成途径及其调控有一个比
较清楚的了解, 才能做到有的放矢, 为核心生物学模
块设计提供理论基础. 其实对植物腺毛研究所产生
的知识已经开始应用于合成生物学/代谢工程方面,
例如, 美国加州大学的 Keasling 课题组[96]有关青蒿
素微生物工业化合成的研究工作堪称是二者结合的
典范. 他们使用酵母菌为宿主, 通过优化酵母中 FPP
合成途径, 引入植物青蒿的紫穗槐二烯合成酶(amor-
phadiene synthase, ADS)P450 单加氧酶基因(该酶
可完成 3步连续的氧化反应, 催化紫穗槐二烯生成青
蒿酸), 并对有关代谢途径作了重新设计, 解决了天
然或非天然代谢物大量积累对寄主的毒性问题,
造后的菌株合成青蒿酸的能力提高 100 mg/L. 2011
One World Health 公司(非盈利性质)开始决定将这
项技术用于实际生产(www.oneworldhealth.org/
malaria, 最新技术进展请参考文献[97]). 在这个例子
中涉及的 ADS P450 单加氧酶克隆和生化功能鉴定
是整个项目的核心部分, 也是进行青蒿酸生物合成
人工设计的理论基础, 需要指出的是这 2个基因都是
在青蒿腺毛中特异性高表达. 最近法国里昂大学的
Legendre 课题组[98]从鼠尾草(Salvia sclarea L.)花的腺
毛中功能鉴定了参与香紫苏醇(sclared)生物合成途径
的两步萜类合成酶: SsdiTPS3 SsLPPS. 香紫苏醇
是龙涎香(ambergris)生物合成前体物质, 而龙涎香主
要用做香水的定香剂, 价值很高; 其主要成分是二萜
类化合物. 随后该课题组[99] 利用合成生物学的技术
手段将香紫苏醇在大肠杆菌中进行重组优化, 在发
酵条件下其产量可达 1.5 g/L.
中国科学: 生命科学 2015 45 6
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酵母系统中天然存在用于萜类异源合成的前体
供应途径
MVA 途径, 而且由于它既具有原核生
物繁殖快、易培养、便于基因工程操作等特点, 又具
有真核生物的蛋白质加工、翻译后修饰、适合植物蛋
白表达等功能, 因而是萜类异源生物合成的理想宿
[100]. 萜类化合物在酵母中的异源生物合成已成为
热门研究并取得了很大的进展[96,101~106]. 然而, 萜类
异源合成尚处于产率较低的水平, 其前体异戊烯基
焦磷酸 IPP DMAPP 供应不足是其中一个主要限制
因素. 因此, 深入研究并提高 DMAPP 前体供应,
获得下游萜烯类化合物高产的重要保障.
众所周知, 简单的代谢工程策略对于多基因决
定的性状难以达到理想效果, 而且难以发现那些与
目标产物合成不直接相关的有效靶点. 近年来, 基因
组尺度代谢模型(genome-scale metabolic model,
GSMM)的重建使菌种改造研究提升到系统水平[107].
基于 GSMM, 采用流量平衡分析(flux balance analy-
sis, FBA)[108,109]in silico 分析方法, 可以发现一些
影响目标产物合成的潜在关键基因靶点, 尤其是代
谢网络中看似与产物合成不相关的靶点. 通过计算
机辅助的理性分析和设计, 可以有效减少实验的盲
目性, 提高工作效率并降低实验成本.
4 展望
植物腺毛中的次生代谢产物在植物生长发育、
境适应、抵御病虫害等方面发挥重要作用, 这些天然
产物也是地球上最丰富的有机化合物. 随着各种组
学的快速发展, 特别是代谢组学分析技术, 为人们
从整体水平上定性、定量和动态地分析代谢过程和
代谢产物创造了良好条件. 近十几年来, 人们在腺
毛特异化合物的分离、鉴定和应用、生物合成相关功
能基因研究、代谢基因工程等各方面取得了巨大进展.
结合现状, 未来植物腺毛次生代谢研究的重点主要
包括(但不局限于)以下几个方面.
4.1 腺毛研究的模式植物
拟南芥(Arabidopsis thaliana)作为研究非腺毛发
育的模式植物已经为植物学家所熟知. 系统研究腺
毛相关的生物学问题同样需要一个模式植物. 参照
模式植物的标准(基因组已知、容易转化、自然群体
及其它遗传材料丰富等), 番茄是一个不二之选(青蒿
也是一个选项, 但至今尚没有青蒿的全基因组信息
公布, 相关遗传资源也不丰富). 番茄作为研究腺毛
的模式植物, 除了符合上述条件外, 最近 Micro-Tom
番茄的引入(植株矮小、生长密度高、生命周期短、
容易被高效转化)使利用番茄进行大规模的分子操作
和筛选成为可能[110]. 利用番茄这个模式植物, 人们
就可以对腺毛如何起始、发生和发育这一系列重要生
物学问题进行系统解析, 同时利用改变腺毛合成次
生代谢产物的能力(如提高腺毛的密度、引入新的次
生代谢产物等)达到提高植物抗虫等目的[111]. 需要指
, 不同品种的番茄具有不同类型的腺毛, 而它们可
能合成/储存不同的次生代谢产物, 研究人员应根据
自己的需要选择适合的品种.
4.2 腺毛代谢调控的研究进展(非酶类基因)
尽管解析新的代谢途径和发现新的酶促反应将
是植物次生代谢领域的一个永恒主题, 但转录因子
可以同时调节一条代谢途径上的多个合成酶基因,
在次生代谢生物合成中起重要调控作用. 因此对相
关转录因子的系统研究将加深对腺毛中代谢调控机
, 以及不同代谢途径间的互作关系的认知. 目前从
番茄和青蒿中功能鉴定的转录因子基因已经开始见
诸报道[23,24,112]. 另外, 同一代谢途径的不同部分在同
一细胞中分布于不同的亚细胞器是一个常见的现象,
很多情况下需要转运蛋白来将这几个部分连接起来;
同时转运蛋白也是代谢物在不同组织之间长距离运
输所必需的元素, 对这些相关基因的功能分析也将
加深对代谢网络调控的认识.
大麻的腺毛中大麻素生物合成途径研究和啤酒
花中苦味酸生物合成途径研究都表明, 蛋白与蛋白
的相互作用(包括直接的或间接的; 稳定的或瞬时的)
也是影响相关代谢途径合成效率的主要因素之一,
这种蛋白层面的调控因素, 与相关基因的腺毛特异
性高表达共同决定了植物腺毛中特定化合物的高效
合成[72,78].
4.3 腺毛次生代谢研究的合成生物学应用
从以上所提及的一系列成功的例子(如在酵母体
系中重组优化的青蒿素半生物合成, 香紫苏醇生物
合成以及啤酒花的苦味酸生物合成)不难看出, 其实
每一条在植物腺毛中具有经济价值的兴趣化合物
生物合成途径, 都可以被平移到微生物中进行重
李好勋等: 植物腺毛次生代谢产物生物合成的研究进展
564
组优化, 也就是说把化学工厂从植物腺毛搬到微
生物最终达到提高效能和产业化的目的. 大规模转
录组和代谢组数据分析可以使人们对相关代谢途径
在腺毛中高效运行的机制有一个宏观的认识, 同时
这些信息也可以直接应用于微生物底盘品种的改
造、优化, 具有事半功倍的作用.
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Specialized Metabolism in Plant Glandular Trichomes
LI HaoXun & WANG GuoDong
Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China
Trichomes could be found on the surfaces of leaves, stems and other organs of many angiosperm plants. The plant
trichomes were commonly divided into two classes: non-glandular trichomes (not many chemicals could be found
inside) and glandular trichomes which produce large amount of specialized natural products of diverse classes. Thus
plant glandular trichomes are considered as chemical factories due to their metabolic capacity with high efficiency.
This property makes glandular trichomes excellent experimental system for elucidation of the pathways of these
chemicals at enzymatic or regulatory level. The fast development of various -omics techniques has greatly
accelerated this procedure. The purpose of this review is to provide a brief introduction about the methods and
technologies used for the investigation on glandular trichomes, summarize the current progress and highlight the
potential applications of glandular trichome studies into metabolic engineering using the strategy of synthetic
biology.
glandular trichomes, specialized metabolism, -omics technique, synthetic biology
doi: 10.1360/N052015-00073
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