植物CO基因研究进展

CO(constans)是植物开花时间光周期调控途径中的一个重要基因.目前从拟南芥、水稻、油菜、马铃薯等多个物种中都已经克隆到CO同源基因.CO基因在不同物种中具有保守的锌指结构和核定位区域,但是不同植物中的作用机理并不完全相同.序列分析表明该基因在被子植物与裸子植物之间、双子叶植物与单子叶植物之间以及不同科、属的植物之间均有明显分化,说明CO基因可能在植物进化中起到了重要作用.本文综述了近年来有关植物CO基因的研究进展,并对其在物种中的进化进行分析,为CO基因进一步研究提供参考.     

花同源异型MADS-box 基因在被子植物中的功能保守性和多样性

MADS-box基因家族成员作为转录调控因子在被子植物花发育调控中发挥关键作用。本文以模式植物拟南芥(Arabidopsis thaliana) 和水稻 (Oryza sativa)为例, 综述了近10年来对被子植物(又称有花植物)两大主要类群——核心真 双子叶植物和单子叶植物花同源异型MADS-box基因的研究成果, 分析MADS-box基因在被子植物中的功能保守性和多样性,同时探讨双子叶植物花发育的ABCDE模型在多大程度上适用于单子叶植物。     

花同源异型MADS-box基因在被子植物中的功能保守性和多样性

MADS-box基因家族成员作为转录调控因子在被子植物花发育调控中发挥关键作用。本文以模式植物拟南芥（Arabidopsis thaliana）和水稻（Oryza sativa）为例,综述了近10年来对被子植物（又称有花植物）两大主要类群——核心真双子叶植物和单子叶植物花同源异型MADS-box基因的研究成果,分析MADS-box基因在被子植物中的功能保守性和多样性,同时探讨双子叶植物花发育的ABCDE模型在多大程度上适用于单子叶植物。     

植物LEAFY 同源基因的研究进展

本文就近10年来LEAFY(简写为LFY)同源基因的研究进展做了综合分析。通过对19种植物中已分离到的LFY同源基因的序列比较分析发现: LFY同源基因编码区核苷酸和氨基酸序列同源性都较高;在双子叶植物基因组中, 拷贝数却有所不同。该基因的表达特性显示其在不同植物中表达的时间和空间有所差异。根据已知序列推导的氨基酸序列构建的系统进化树表明, 单子叶植物与裸子植物的亲缘关系近于双子叶与裸子植物的亲缘关系。上述研究资料为植物成花机理研究提供了重要参考, 且在研究植物系统进化方面也具有重要的意义。     

木质素生物合成酶CCR基因的生物信息学分析

肉桂酰辅酶A还原酶(Cinnamoyl-CoA reductase,CCR)是催化木质素特异途径的第一个关键酶,是调节碳素流向木质素潜在的控制关节点,对木质素单体的生物合成起着重要作用。通过NCBI数据库收集来自裸子植物、单子叶植物及双子叶植物的35条CCR基因的完整信息,对35条CCR基因的cDNA及其编码的氨基酸序列的进化规律、理化性质、结构域、导肽、信号肽、跨膜结构域、亲/疏水性以及蛋白质结构等性状进行了生物信息学分析与预测,构建了CCR基因的系统发育树。分析结果表明,单子叶植物CCR基因中GC的含量明显高于双子叶植物;CCR基因编码的氨基酸序列存在9个保守区域;所编码氨基酸的理化性质基本一致,但单子叶、双子叶及裸子植物的CCR基因编码主要氨基酸的种类和含量存在着差异;CCR蛋白的N-端存在一个脱氢酶/差向异构酶/辅酶Ⅰ结合蛋白的结构域,无导肽、信号肽及跨膜结构域,属亲水性蛋白;进化树绘制以及同源建模结果表明,CCR基因的进化和植物的进化基本一致,CCR蛋白三级结构模型的空间结构稳定,建模结果可靠。分析结果对于深入研究CCR蛋白在木质素合成中的作用具有一定的理论指导意义。     

植物LEAFY同源基因的研究进展

本文就近10年来LEAFY(简写为LFY)同源基因的研究进展做了综合分析.通过对19种植物中已分离到的LFY同源基因的序列比较分析发现:LFY同源基因编码区核苷酸和氨基酸序列同源性都较高;在双子叶植物基因组中,拷贝数却有所不同.该基因的表达特性显示其在不同植物中表达的时间和空间有所差异.根据已知序列推导的氨基酸序列构建的系统进化树表明,单子叶植物与裸子植物的亲缘关系近于双子叶与裸子植物的亲缘关系.上述研究资料为植物成花机理研究提供了重要参考,且在研究植物系统进化方面也具有重要的意义.     

木薯及其他植物P5CS基因进化及表达分析

该研究采用生物信息学的方法,从木薯等31个已完成基因组测序的植物中,共鉴定出84个吡咯啉-5-羧酸合成酶(P5CS)基因,并对其进行系统发育分析。结果表明:(1)P5CS在内含子长度上差别较大,而在氨基酸长度、外显子数目、等电点和分子量上差别不大。(2)由于发生基因重复,在大多数单子叶和双子叶植物中都有2个P5CS,而且在单子叶和双子叶植物中均发现P5CS1基因聚类在一组,而P5CS2基因聚类在另一组,支持P5CS1和P5CS2基因是独立起源,且该重复事件发生在单子叶和双子叶植物分化之前。(3)在某些植物(如蒺藜苜蓿、大豆等)中存在3~7个P5CS基因,表明在单子叶和双子叶植物分化之后P5CS基因又发生了多次重复事件,并将它们归纳为4种进化模式。(4)木薯中有2个P5CS基因,表达分析显示,MeP5CS1和MeP5CS2在叶片、叶柄、茎、须根和储藏根中均可检测到,其中MeP5CS1在叶片中表达较高,而MeP5CS2在茎和储藏根中表达较高。(5)干旱胁迫下,MeP5CS1仅在第一片完全展开叶中被显著诱导,而MeP5CS2在第一片完全展开叶和老叶中均能被显著诱导;低温胁迫下,MeP5CS1和MeP5CS2在不同组织中均能被显著诱导,但具有不同的表达模式。研究表明,木薯的MeP5CS1和MeP5CS2基因在转录水平受到干旱、低温等非生物胁迫的调控。     

基于5 993个核基因的被子植物系统发育关系研究

系统发育关系的构建对被子植物分类及进化研究非常重要。长期以来,被子植物系统发育的研究,大多使用质体基因、线粒体基因或少数保守的单拷贝核基因。该研究从已注释基因组或转录组中搜集88种被子植物(包含58目)的核基因集;通过对其进行同源基因聚类及去旁系同源基因,获得了5 993个一对一的直系同源基因家族(即对于每个基因家族,每种植物最多一条序列,最少包含50个物种);使用截取各种不同数目基因集的DNA或氨基酸序列,采用串联法(concatenation)和溯祖法(coalescence),共构建了20棵进化树。比较这些进化树,虽然大部分结果支持APG IV中描述的被子植物主要支系之间的关系[(真双子叶植物,单子叶植物),木兰类植物],但真双子叶植物内部各目分支的演化关系与APG IV有一个很大的不同,即认为檀香目和石竹目是蔷薇类植物的姊妹群。基于这些进化树,估算了被子植物各目分支的分化时间,结果表明被子植物的起源时间为237.78百万年前(95%置信区间为202.6～278.08),与主流观点认为的225百万年至240百万年前一致。以上结果为构建进化树提供了一种可行性策略,这种方法允许使用基因数目更多而计算速度更快。     

单子叶植物高级分类阶元系统演化: matK、rbcL和18S rDNA序列的证据

基于两个叶绿体基因（matK和rbcL）和一个核糖体基因（18S rDNA）的序列分析,对代表了基部被子植物和单子叶植物主要谱系分支的86科126属151种被子植物（单子叶植物58科86属101种）进行了系统演化关系分析。研究结果表明由胡椒目Piperales、樟目Laurales、木兰目Magnoliales和林仙目Canellales构成的真木兰类复合群是单子叶植物的姐妹群。单子叶植物的单系性在3个序列联合分析中得到98％的强烈自展支持。联合分析鉴定出9个单子叶植物主要谱系（广义泽泻目Alismatales、薯蓣目Dioscorcales、露兜树目Pandanales、天门冬目Asparagalcs、百合目Liliales、棕榈目Arecales、禾本目Poales、姜目Zingiberales、鸭跖草目Commelinales）和6个其他被子植物主要谱系（睡莲目Nymphaeales、真双子叶植物、木兰目、樟目、胡椒目、林仙目）。在单子叶植物内,菖蒲目Acorales（菖蒲属Acorus）是单子叶植物最早分化的一个谱系,广义泽泻目（包括天南星科Araceae和岩菖蒲科Toficldiaccae）紧随其后分化出来,二者依次和其余单子叶植物类群构成姐妹群关系。无叶莲科Petrosaviaceac紧随广义的泽泻目之后分化出来,无叶莲科和剩余的单子叶植物类群形成姐妹群关系,并得到了较高的支持率。继无叶莲科之后分化的类群形成两个大的分支：一支是由露兜树目和薯蓣目构成,二者形成姐妹群关系：另一支是由天门冬目、百合目和鸭跖草类复合群组成,三者之间的关系在单个序列分析和联合分析中不稳定,需要进一步扩大取样范围来确定。在鸭跖草类复合群分支内,鸭跖草目和姜目的姐妹群关系在3个序列联合分析和2个序列联合分析的严格一致树中均得到强烈的自展支持,获得的支持率均是100％。但是,对于棕榈目和禾本目在鸭跖草类中的系统位置以及它们和鸭跖草目-姜目之间的关系,有待进一步解决。值得注意的是,无叶莲科与其他单子叶植物类群（除菖蒲目和泽泻目外）的系统关系在本文中获得较高的自展支持率,薯蓣目和天门冬目的单系性在序列联合分析中都得到了较好的自展支持,而这些在以往的研究中通常支持率较低。鉴于菖蒲科和无叶莲科独特的系统演化位置,本文支持将其分别独立成菖蒲目和无叶莲目Petrosavialcs的分类学界定。     

甘菊BADH基因cDNA的克隆及在盐胁迫下的表达

利用PCR、RT—PCR和PCR—RACE技术,从菊科植物甘菊（Dendranthema lavandulifolium）中克隆到2个甜菜碱醛脱氢酶（betaine aldehyde dehydrogenase,BADH）基因的同源基因,分别命名为DlBADH1和DlBADH2,GenBank登录号分别为DQ011151和DQ011152。DlBADH1的cDNA全长1821bp,其开放阅读框编码503个氨基酸的蛋白质;DlBADH2全长1918bp,编码506个氨基酸的蛋白质。两个基因核苷酸序列的同源性为97％,推导的氨基酸序列的同源性为98％。与已发表的其它植物BADH基因氨基酸序列的同源性在64％以上。在推导的氨基酸序列中,均含有醛脱氢酶所具有的高度保守的十肽（VTLELGGKSP）以及与酶功能有关的半胱氨酸残基（C）。在推导的氨基酸序列的系统关系中,甘菊位于其它双子叶植物和单子叶植物之间,与其植物分类的系统关系相吻合。RT—PCR—Southern半定量表达分析表明,甘菊BADH基因家族中存在表达受盐诱导的成员。     

Cellulose biosynthesis in plants: from genes to rosettes

Modern techniques of gene cloning have identified the CesA genes as encoding the probable catalytic subunits of the plant CelS, the cellulose synthase enzyme complex visualized in the plasma membrane as rosettes. At least 10 CesA isoforms exist in Arabidopsis and have been shown by mutant analyses to play distinct role/s in the cellulose synthesis process. Functional specialization within this family includes differences in gene expression, regulation and, possibly, catalytic function. Current data points towards some CesA isoforms potentially being responsible for initiation or elongation of the recently identified sterol beta-glucoside primer within different cell types, e.g. those undergoing either primary or secondary wall cellulose synthesis. Different CesA isoforms may also play distinct roles within the rosette, and there is some circumstantial evidence that CesA genes may encode the catalytic subunit of the mixed linkage glucan synthase or callose synthase. Various other proteins such as the Korrigan endocellulase, sucrose synthase, cytoskeletal components, Rac13, redox proteins and a lipid transfer protein have been implicated to be involved in synthesizing cellulose but, apart from CesAs, only Korrigan has been definitively linked with cellulose synthesis. These proteins should prove valuable in identifying additional CelS components.     

Higher plant cellulose synthases

Cellulose, an aggregate of unbranched polymers of β-1,4-linked glucose residues, is the major component of wood and thus paper, and is synthesized by plants, most algae, some bacteria and fungi, and even some animals. The genes that synthesize cellulose in higher plants differ greatly from the well-characterized genes found in Acetobacter and Agrobacterium sp. More correctly designated as 'cellulose synthase catalytic subunits', plant cellulose synthase (CesA) proteins are integral membrane proteins, approximately 1,000 amino acids in length. The sequences for more than 20 full-length CesA genes are available, and they show high similarity to one another across the entire length of the encoded protein, except for two small regions of variability. There are a number of highly conserved residues, including several motifs shown to be necessary for processive glycosyltransferase activity. No crystal structure is known for cellulose synthase proteins, and the exact enzymatic mechanism is unknown. There are a number of mutations in cellulose synthase genes in the model organism Arabidopsis thaliana. Some of these mutants show altered morphology due to the lack of a properly developed primary or secondary cell wall. Others show resistance to well-characterized cellulose biosynthesis inhibitors.     

Building the wall: genes and enzyme complexes for polysaccharide synthases

The complete sequence of the Arabidopsis genome has revealed a total of 40 cellulose synthase (CesA) and cellulose synthase-like (Csl) genes. Recent studies suggest that each CESA polypeptide contains only one catalytic center, and that two or more polypeptides from different genes might be needed to form a functional cellulose synthase complex.     

Modulation of the cellulose content of tuber cell walls by antisense expression of different potato (Solanum tuberosum L.) CesA clones

Four potato cellulose synthase (CesA) homologs (StCesA1, 2, 3 and 4) were isolated by screening a cDNA library made from developing tubers. Based on sequence comparisons and the fact that all four potato cDNAs were isolated from this single cDNA-library, all four StCesA clones are likely to play a role in primary cell wall biosynthesis. Several constructs were generated to modulate cellulose levels in potato plants in which the granule-bound starch synthase promoter was used to target the modification to the tubers. The StCesA3 was used for up- and down-regulation of the cellulose levels by sense (SE-StCesA3) and antisense (AS-StCesA3) expression of the complete cDNA. Additionally, the class-specific regions (CSR) of all four potato cellulose synthase genes were used for specific down-regulation (antisense) of the corresponding CesA genes (csr1, 2, 3 and 4). None of the transformants showed an overt developmental phenotype. Sections of tubers were screened for altered cell wall structure by Fourier Transform Infrared microspectroscopy (FTIR) and exploratory Principal Component Analysis (PCA), and those plants discriminating from WT plants were analysed for cellulose content and monosaccharide composition. Several transgenic lines were obtained with mainly decreased levels of cellulose. These results show that the cellulose content in potato tubers can be reduced down to 40% of the WT level without affecting normal plant development, and that constructs based on the CSR alone are specific and sufficient to down-regulate cellulose biosynthesis.     

Three loblolly pine CesA genes expressed in developing xylem are orthologous to secondary cell wall CesA genes of angiosperms

Specific plant cellulose synthases (CesA), encoded by a multigene family, are necessary for secondary wall synthesis in vascular tissues and are critical to wood production. We obtained full-length clones for the three CesAs that are highly expressed in developing xylem and examined their phylogenetic relationships and expression patterns in loblolly pine tissues. Full-length CesA clones were isolated from cDNA of developing loblolly pine (Pinus taeda) xylem and phylogenetic inferences made from plant CesA protein sequences. Expression of the three genes was examined by Northern blot analysis and semiquantitative RT-PCR. Each of three PtCesA genes is orthologous to one of the three angiosperm secondary cell wall CesAs. The PtCesAs are coexpressed in tissues of loblolly pine with tissues undergoing secondary cell wall biosynthesis showing the highest levels of expression. Phylogenetic and expression analyses suggest that functional roles for these loblolly pine CesAs are analogous to those of orthologs in angiosperm taxa. Based upon evidence from this and other studies, we suggest division of seed plant CesA genes into six major paralogous groups, each containing orthologs from various taxa. Available evidence suggests that paralogous CesA genes and their distinct functional roles evolved before the divergence of gymnosperm and angiosperm lineages.     

Control of cellulose synthase complex localization in developing xylem

Cellulose synthesis in the developing xylem vessels of Arabidopsis requires three members of the cellulose synthase (CesA) gene family. In young vessels, these three proteins localize within the cell, whereas in older vessels, all three CesA proteins colocalize with bands of cortical microtubules that mark the sites of secondary cell wall deposition. In the absence of one subunit, however, the remaining two subunits are retained in the cell, demonstrating that all three CesA proteins are required to assemble a functional complex. CesA proteins with altered catalytic activity localize normally, suggesting that cellulose synthase activity is not required for this localization. Cortical microtubule arrays are required continually to maintain normal CesA protein localization. By contrast, actin microfilaments do not colocalize with the CesA proteins and are unlikely to play a direct role in their localization. Green fluorescent protein-tagged CesA reveals a novel process in which the structure and/or local environment of the cellulose synthase complex is altered rapidly.