一种植物细胞壁松驰蛋白:膨胀素

在植物细胞的生长过程中 ,多糖和蛋白质分泌到细胞壁里层 ,并形成具有一定机械强度的网络 ,这个网络是能伸展的 ,除非细胞停止生长。在细胞的生长过程中 ,一种细胞壁蛋白—膨胀素首次被鉴定出来具有使细胞壁的多糖网络疏松的能力 ,从而使膨压驱动的细胞扩大。膨胀素由两个多基因家族即α -膨胀素和 β -膨胀素多基因家族编码 ,每种基因的表达具有部位和细胞类型的特异性 ,但最新的研究也表明拟南芥中的膨胀素可以分为三个亚家族。越来越多的膨胀素基因从各种植物中鉴定出来 ,系统分析显示它们可能从一个共同的祖先基因进化而来。膨胀素的作用机理研究的还不是很清楚 ,但因为它们具有特别的功能 ,因此展现出良好的工业化应用前景。     

膨胀素在植物生长发育中的作用

膨胀素是一类具有非水解活性的细胞壁松弛蛋白,参与植物生长发育过程中细胞壁的修饰。大多数植物中都发现有膨胀素基因家族成员存在,其功能涉及植物生长发育的各个方面,包括营养生长、形态发生、受精授粉、果实成熟等,并表现出高度的组织、器官和细胞特异性。本文综述膨胀素在种子萌发、叶的发育、根茎生长、花的发育等生长发育过程中的作用。     

膨胀素的结构与功能

膨胀素是植物细胞生长期间释放的一种能使细胞壁松弛的蛋白质,是细胞壁伸展的关键调节剂,对细胞生长有重要作用。膨胀素由庞大的基因家族编码,分为α-、β-、γ-和δ-膨胀素。膨胀素有多种功能,研究它对搞清生长机制有着重要的意义。     

植物细胞壁研究进展

植物细胞壁是一种复杂的网状结构,其成分包含纤维素、半纤维素、果胶和少量的结构蛋白等。在植物细胞生长过程中,细胞能产生伸展素蛋白,打断纤维素和半纤维素之间的氢键,引起细胞膨压驱动的细胞壁扩张。成熟细胞壁扩张性的丧失是由于细胞壁硬化作用而对扩张性蛋白的作用不敏感造成的,细胞壁成熟过程中很多不同的连接会同时发生,当细胞壁基质多聚体分子之间的连接增加到一定的程度。细胞壁的伸长就会被完全抑制。     

植物抗真菌病害基因工程研究进展

从表达水解酶、植物病程相关蛋白、抗真菌蛋白、病原毒性因子失活蛋白、抗病基因、植保素合成限速酶、植物细胞壁结构修饰分子、植物抗生反应调节基因等角度综述了植物抗真菌病害基因工程的策略,并就各种策略的研究进展,存在问题和发展趋势进行了探讨。     

大豆幼苗下胚轴扩张蛋白的存在及其特性

用离体细胞壁伸展活性重组法,对大豆（Ｇｌｙｃｉｎｅｍａｘ（Ｌ．）Ｍｅｒ．）幼苗下胚轴细胞壁特异性扩张蛋白的活性鉴定和特性研究结果表明,大豆幼苗下胚轴的延伸生长,既与扩张蛋白的活性升高有关,也与其细胞壁对扩张蛋白的敏感性增加有关;热钝化大豆下胚轴细胞壁的伸展活性,一旦被外源扩张蛋白所恢复,用酸性缓冲液（ｐＨ４．５）代替扩张蛋白提取液,伸展活性不受影响;但若换用中性缓冲液（ｐＨ６．８）,伸展活性丧失殆尽,且与活细胞壁一样,随缓冲液的交替更换而反复逆转;大豆和黄瓜幼苗扩张蛋白可以与其热钝化的细胞壁相互交叉重组。另外,重组的细胞壁伸展活性对扩张蛋白浓度和ｐＨ的依赖性,符合一般酶的催化特征,说明扩张蛋白不仅在植物细胞的延伸生长过程中起着极为重要的作用,而且还暗示植物细胞壁的内源伸展就是该蛋白介导的一种生物化学过程。     

植物细胞壁中的伸展蛋白

随着实验技术的发展尤其是分子生物学技术的应用 ,植物细胞壁的研究已取得丰硕的成果。植物细胞壁中最重要的结构蛋白———伸展蛋白 ,是高等植物细胞壁中一族富含羟脯氨酸的糖蛋白 ,起强固细胞壁的作用。本文综述了近几十年对伸展蛋白的分离纯化、结构、生物合成、功能作用及其基因和表达的控制方面的研究     

扩展蛋白与激素调控的生长发育

扩展蛋白是一类具有细胞壁松弛功能的蛋白质,它不仅能调节细胞壁的松弛和伸张,而且在调控植物的生长发育以及逆境响应过程中具有重要的作用。扩展蛋白作为激素调节因子能够对多种激素产生响应,从而调节植物的生长发育:扩展蛋白参与了乙烯调节的植物生长发育过程;改变植物内源的生长素水平或用外源生长素进行处理同样影响扩展蛋白基因的表达;扩展蛋白可能参与赤霉素和脱落酸调节的生长发育和逆境响应过程;此外,施加外源的茉莉酸甲酯、油菜素内酯和细胞分裂素也会影响扩展蛋白基因的表达水平。本文综述了扩展蛋白在激素介导的植物生长发育方面的最新研究进展,以期为研究者更直观便捷的了解该方面现状提供依据。     

《Molecular Plant》文章中文摘要

题目：植物细胞壁基质（matrix）多糖的生物合成（综述） 摘要：伸长中的植物细胞的细胞壁主要由纤维素微纤丝和基质多糖（半纤维素和果胶）以及少量结构蛋白和酶蛋白组成。基质多糖在高尔基体中合成,通过胞吐作用输送到细胞壁,并与纤维素微纤丝相嵌。纤维素微纤丝在细胞膜上合成并直接沉积到细胞壁。已知在生长素诱导的伸长细胞中,高尔基体中存在多糖链合成,然而直到最近才鉴定出合成多糖链酶的相关基因。在基因鉴定研究中,     

植物细胞壁伸展蛋白的功能与利用

伸展蛋白是一类富含羟脯氨酸的糖蛋白,是植物细胞壁中重要的结构蛋白。伸展蛋白家族基因广泛存在于多种植物中,参与植物细胞壁网络结构形成与修饰、植物细胞伸长、根生长发育等过程,并且影响植物机械强度、倒伏抗性和各种逆境胁迫反应。本文拟从蛋白结构、进化关系、生物学功能等方面介绍植物伸展蛋白近期研究进展,并初步提出了此类基因在农作物和能源植物遗传改良中的利用。     

The expansin superfamily

The expansin superfamily of plant proteins is made up of four families, designated α-expansin, β-expansin, expansin-like A and expansin-like B. α-Expansin and β-expansin proteins are known to have cell-wall loosening activity and to be involved in cell expansion and other developmental events during which cell-wall modification occurs. Proteins in these two families bind tightly to the cell wall and their activity is typically assayed by their stimulation of cell-wall extension and stress relaxation; no bona fide enzymatic activity has been detected for these proteins. α-Expansin proteins and some, but not all, β-expansin proteins are implicated as catalysts of 'acid growth', the enlargement of plant cells stimulated by low extracellular pH. A divergent group of β-expansin genes are expressed at high levels in the pollen of grasses but not of other plant groups. They probably function to loosen maternal cell walls during growth of the pollen tube towards the ovary. All expansins consist of two domains; domain 1 is homologous to the catalytic domain of proteins in the glycoside hydrolase family 45 (GH45); expansin domain 2 is homologous to group-2 grass pollen allergens, which are of unknown biological function. Experimental evidence suggests that expansins loosen cell walls via a nonenzymatic mechanism that induces slippage of cellulose microfibrils in the plant cell wall.     

pH and expansin action on single suspension-cultured tomato (Lycopersicon esculentum) cells

The aim of this study was to measure key material properties of the cell walls of single suspension-cultured plant cells and relate these to cell-wall biochemistry. To this end, micromanipulation was used to compress single tomato cells between two flat surfaces until they ruptured, and force-deformation data were obtained. In addition to measuring the bursting force, we also determined the elastic (Young’s) modulus of the cell walls by matching low strain (≤20% deformation) experimental data with a cell compression model, assuming linear elastic cell walls. The walls were most elastic at pH 4.5, the pH optimum for expansin activity, with an elastic modulus of 2.0 ± 0.1 GPa. Following the addition of exogenous expansins, cell walls became more elastic at all pH values. Western blot analysis of proteins from walls of cultured cells revealed the presence of expansin epitopes, suggesting that the inherent pH dependence of elasticity and other compression phenomena is related to the presence of endogenous expansin proteins and their wall-loosening ability. Although strict application of the linear-elastic model could not be applied to large deformations—for example, up to cell bursting—because of irreversible behaviour, the deviation of the data from the model was generally small enough to allow estimation of the strain in the cell wall at failure. This strain was greater at pH 4.5 and when expansins were added to the suspension. The changes in elasticity are consistent with suggestions about the mode of expansin action. The estimated strains at failure are compatible with data on the failure of Acetobacter-derived cellulose–xyloglucan composites and proposed mechanisms of such failure. Through the measurement of cell-wall material properties using micromanipulation, it may be possible to understand more fully how cell-wall composition, structure and biochemistry lead to cell mechanical behaviour.     

Expression of expansin genes is correlated with growth in deepwater rice.

Expansins are a family of proteins that catalyze long-term extension of isolated cell walls. Previously, two expansin proteins have been isolated from internodes of deepwater rice, and three rice expansin genes, Os-EXP1, Os-EXP2, and Os-EXP3, have been identified. We report here on the identification of a fourth rice expansin gene, Os-EXP4, and on the expression pattern of the rice expansin gene family in deepwater rice. Rice expansin genes show organ-specific differential expression in the coleoptile, root, leaf, and internode. In these organs, there is increased expression of Os-EXP1, Os-EXP3, and Os-EXP4 in developmental regions where elongation occurs. This pattern of gene expression is also correlated with acid-induced in vitro cell wall extensibility. Submergence and treatment with gibberellin, both of which promote rapid internodal elongation, induced accumulation of Os-EXP4 mRNA before the rate of growth started to increase. Our results indicate that the expression of expansin genes in deepwater rice is differentially regulated by developmental, hormonal, and environmental signals and is correlated with cell elongation.     

Growth maintenance of the maize primary root at low water potentials involves increases in cell-wall extension properties, expansin activity, and wall susceptibility to expansins

Previous work on the growth biophysics of maize (Zea mays L.) primary roots suggested that cell walls in the apical 5 mm of the elongation zone increased their yielding ability as an adaptive response to low turgor and water potential (psi w). To test this hypothesis more directly, we measured the acid-induced extension of isolated walls from roots grown at high (-0.03 MPa) or low (-1.6 MPa) psi w using an extensometer. Acid-induced extension was greatly increased in the apical 5 mm and was largely eliminated in the 5- to 10-mm region of roots grown at low psi w. This pattern is consistent with the maintenance of elongation toward the apex and the shortening of the elongation zone in these roots. Wall proteins extracted from the elongation zone possessed expansin activity, which increased substantially in roots grown at low psi w. Western blots likewise indicated higher expansin abundance in the roots at low psi w. Additionally, the susceptibility of walls to expansin action was higher in the apical 5 mm of roots at low psi w than in roots at high psi w. The basal region of the elongation zone (5-10 mm) did not extend in response to expansins, indicating that loss of susceptibility to expansins was associated with growth cessation in this region. Our results indicate that both the increase in expansin activity and the increase in cell-wall susceptibility to expansins play a role in enhancing cell-wall yielding and, therefore, in maintaining elongation in the apical region of maize primary roots at low psi w.     

The Existence of Expansin and Its Properties in the Hypocotyls of Soybean Seedlings

Expansins, a newly discovered class of cell wall proteins, were the only proteins that, to date, have been shown to have the ability to restore the "acid growth" response of the heat-inactivated cell wall in an in vitro assay. In order to characterize these proteins, an automatic extensometer had been previously constructed by modification of an equal-arm mechanical balance with a linear variable differential transformer (LVDT) and with some easily available laboratory equipment. The objective of this study was to confirm and complement the work on expansin in cucumber ( Cucumis sativus L. ) seedlings carried out in the expansin-discoverers' laboratory and in addition, to further examination of the extensometer built in the authors' laboratory. It was reported that, firstly, expansin activity was maximal in cell wall from the growing region of soybean (Glycine max L. ) hypocotyls but was negligible or lacking in that from mature, basal regions and cotyledons. Corre- spondingly, walls from the growing tissue had a strong susceptibility to the action of expansin, whereas the nongrowing tissues became insensitive to the expansin action. It was concluded that the growth of soybean hypocotyl was associated with an increase in both expansin activity and wall susceptibility to the expansin action. Secondly, the heat-inactivated wall extension could be induced by cross reconstitution with crude expansin extract between soybean and cucumber species. Thirdly, once the heat-inactivated wall has been pretreated with the exogenous expansin, the reconstituted wall required no further expansin for extension indicating that exogenous expansin could specifically bind to cell wall and be enough to repeatedly exert its action without releasing from the cell wall into the external solution, i.e., a single expansin molecule could gradually break a series of load-bearing bonds one by one while moving along the cell wall, and thereby permitting the wall to extend. Fourthly, reconstitution of the wall extension activity was evidently dependent on the expansin concentration and the pH of the bathing solution, which was consistent with the catalytic characteristics of classical enzymes. Finally, endogenous and reconstituted wall extension could be significantly induced in 50 mmoL/L sodium acetate at pH 4.5 and completely inhibited in 50 mmol/L Hepes at pH 6.8, especially these phenomena could continuously be caused by switching incubation buffer from one to the other alternately, suggesting that change in pH of bathing solution could only affect the conformation of expansin (thus leading to denaturation or renaturation of it) but not the affinity of it for cell wall. In summary, these observations lend further support to the fact that expansin could mediate the acid-induced extension of the isolated wall, probably through a biochemical or enzymatic process exerting directly to the cell wall. This protein may play an essential role in the control of plant cell growth in vivo.     

Variable expansin expression in Arabidopsis leads to different growth responses

Expansins have long been implicated in the control of cell wall extensibility. However, despite ample evidence supporting a role for these proteins in the endogenous mechanism of plant growth, there are also examples in the literature where the outcome of altered expansin gene expression is difficult to reconcile with a simplistic causal linkage to growth promotion. To investigate this problem, we report on the analysis of transgenic Arabidopsis plants in which a heterologous cucumber expansin can be inducibly overexpressed. Our results indicate that the effects of expansin expression on growth depend on the degree of induction of expansin expression and the developmental pattern of organ growth. They support the role of expansin in directional cell expansion. They are also consistent with the idea that excess expansin might itself impede normal activities of cell wall modifications, culminating in both growth promotion and repression depending on the degree of expression.     

Genome histories clarify evolution of the expansin superfamily: new insights from the poplar genome and pine ESTs

Expansins comprise a superfamily of plant cell wall-loosening proteins that has been divided into four distinct families, EXPA, EXPB, EXLA and EXLB. In a recent analysis of Arabidopsis thaliana and Oryza sativa expansins, we proposed a further subdivision of the families into 17 clades, representing independent lineages in the last common ancestor of monocots and eudicots. This division was based on both traditional sequence-based phylogenetic trees and on position-based trees, in which genomic locations and dated segmental duplications were used to reconstruct gene phylogeny. In this article we review recent work concerning the patterns of expansin evolution in angiosperms and include additional insights gained from the genome of a second eudicot species, Populus trichocarpa, which includes at least 36 expansin genes. All of the previously proposed monocot-eudicot orthologous groups, but no additional ones, are represented in this species. The results also confirm that all of these clades are truly independent lineages. Furthermore, we have used position-based phylogeny to clarify the history of clades EXPA-II and EXPA-IV. Most of the growth of the expansin superfamily in the poplar lineage is likely due to a recent polyploidy event. Finally, some monocot-eudicot clades are shown to have diverged before the separation of the angiosperm and gymnosperm lineages. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Expansins in Plant Growth and Development: an Update on an Emerging Topic

Abstract: Expansins are a class of proteins identified by their ability to induce the extension of isolated plant cell walls. Expansins are encoded by an extensive multigene family in higher plants, several members of which have been shown to be expressed in a tissue-specific manner. Besides playing an apparently key role in wall expansion, and hence in cell growth, expansins have been implicated in an increasing number of processes during plant growth and development. These include: leaf organogenesis, fruit softening, and wall disassembly. A second class of closely related proteins (referred to as β-expansins) has been identified. Other recent advances in expansin research include the recovery of transgenic plants with altered level of expansins, and the production of recombinant expansins in het-erologous expression systems.     

Detection of expansin proteins and activity during tomato fruit ontogeny

Expansins are plant proteins that have the capacity to induce extension in isolated cell walls and are thought to mediate pH-dependent cell expansion. J.K.C. Rose, H.H. Lee, and A.B. Bennett ([1997] Proc Natl Acad Sci USA 94: 5955-5960) reported the identification of an expansin gene (LeExp1) that is specifically expressed in ripening tomato (Lycopersicon esculentum) fruit where cell wall disassembly, but not cell expansion, is prominent. Expansin expression during fruit ontogeny was examined using antibodies raised to recombinant LeExp1 or a cell elongation-related expansin from cucumber (CsExp1). The LeExp1 antiserum detected expansins in extracts from ripe, but not preripe tomato fruit, in agreement with the pattern of LeExp1 mRNA accumulation. In contrast, antibodies to CsExp1 cross-reacted with expansins in early fruit development and the onset of ripening, but not at a later ripening stage. These data suggest that ripening-related and expansion-related expansin proteins have distinct antigenic epitopes despite overall high sequence identity. Expansin proteins were detected in a range of fruit species and showed considerable variation in abundance; however, appreciable levels of expansin were not present in fruit of the rin or Nr tomato mutants that exhibit delayed and reduced softening. LeExp1 protein accumulation was ethylene-regulated and matched the previously described expression of mRNA, suggesting that expression is not regulated at the level of translation. We report the first detection of expansin activity in several stages of fruit development and while characteristic creep activity was detected in young and developing tomato fruit and in ripe pear, avocado, and pepper, creep activity in ripe tomato showed qualitative differences, suggesting both hydrolytic and expansin activities.