新型植物生长调节物质——激素性多肽的研究进展

多肽是生物体内一种非常重要的物质,它以信号的形式调控着生物的生活周期。在动物、细菌、真菌上作为激素、信息素和生长因子已进行了广泛的研究。然而,在植物上１９９１年才首次报道名叫系统素的伤害信号物质的内生多肽。最近,已从植物中分离出多种肽性植物生长调节因子。本文简要介绍系统素、早期结瘤素、植物硫素、豆胰岛素等四种激素性多肽的发现与分离,以及其结构与生理作用。     

新型植物生长调节物质——激素性多肽的研究进展

多肽是生物体内一种非常重要的物质,它以信号的形式调控着生物的生活周期。在动物、细菌、真菌上作为激素、信息素和生长因子已进行了广泛的研究。然而,在植物上1991年才首次报道名叫系统素的伤害信号物质的内生多肽。最近,已从植物中分离出多种肽性植物生长调节因子。本文简要介绍系统素、早期结瘤素、植物硫素、豆胰岛索等四种激素性多肽的发现与分离,以及其结构与生理作用。     

植物多肽信号分子的特点和功能

近几年研究表明,植物体内存在类似动物和酵母的多肽信号分子,调控植物生长发育以及对环境的响应.介绍了植物中的系统素、迅速碱化因子(RALF)、早期结瘤蛋白40(ENOD40)、植物磺化激动素(PSK)、S位点富含半胱胺酸蛋白(SCR)、CLV3以及相应受体的特点和功能研究进展,并且对多肽信号在植物中的作用及其应用前景进行了探讨.     

油菜素甾醇类信号转导受体研究进展

在植物和动物的生长发育过程中,甾醇和肽类激素被广泛地作为信号转导分子来使用。在植物中,油菜素甾醇类（BRs）信号由细胞表面受体激酶BRI1感知,该受体与动物的甾醇受体有明显的区别。对BR信号转导途径中组分的鉴定表明,该途径与其地动物和植物信号转导途径具有类似性。近来的研究证实番茄BRI1（tBRIl）能感知BR和肽类激素系统素。于是,关于受体一配体特异性的分子机制及进化的问题便产生了。本文就目前关于BRs信号转导中受体的研究进展作一综述。     

植物硫氧还蛋白系统

硫氧还蛋白是一类催化二硫键氧化还原的小蛋白,它通过调控细胞中氧化还原状态发挥重要的作用。在植物中,硫氧还蛋白系统尤为复杂,参与了植物的新陈代谢、转录翻译调控、信号传导以及植物的抗逆反应等。本文主要通过对植物硫氧还蛋白分类、活性位点、结构以及3种硫氧还蛋白系统研究现状进行概述,并对植物的硫氧还蛋白及系统进行了展望,从而较为全面地综述了植物的硫氧还蛋白系统,为进一步了解硫氧还蛋白在植物体内的作用机制奠定基础,也为今后的相关研究提供参考。     

植物多肽激素

近几年研究表明,植物体内存在类似动物和酵母的多肽信号分子,调控植物生长发育以及调节植物对环境的响应。本文介绍了植物中的系统素,RALF,ENOD40,PSK,SCR,SLV3的特点和功能研究进展。     

生物和非生物逆境胁迫下的植物系统信号

复杂多变的自然环境使植物进化出许多适应策略, 其中由局部胁迫引起的系统响应广泛存在, 精细调节植物的生长发育和环境适应能力。植物系统响应的诱导因素首先引起植物从局部到全株范围的信号转导, 这类信号称为系统信号。当受到外界刺激时, 植物首先在受刺激细胞内触发化学信号分子的变化, 如茉莉酸和水杨酸甲酯等在浓度和信号强度方面发生变化; 进而, 伴随着一系列复杂的信号转换, 多种信号组分共同完成系统响应的激活。植物激素、小分子肽和RNA等被认为是缓慢系统信号通路中的关键组分, 而目前也有大量研究阐释了由活性氧、钙信号和电信号相互偶联组成的快速系统信号通路。植物系统信号对其生存和繁衍至关重要, 其精确的转导机制仍值得深入研究。该文综述了植物响应环境的系统信号转导研究进展, 对关键的系统信号组分及其转导机制进行了总结, 同时对植物系统信号传递的研究方向进行了展望。     

植物维管系统形成的调节机制

植物维管系统形成与分化包含着贯穿植物生长发育全过程的一系列细胞分裂与分化事件。这些事件的发生和发展过程受到很多遗传和其他内源因子的调控。对维管系统形成及其调控的认识近年来获得了较大的进展。研究表明植物激素、转录因子、短肽信号分子和microRNA等在植物维管系统建成中发挥重要调控作用。     

植物小分子肽的研究进展

植物信号肽的研究主要集中在小分子肽。小分子肽作为胞间通讯的关键成分,主要参与信号干扰、反应途径、显示抗菌活性,并以配体的形式与细胞膜表面的受体激酶相互作用,从而实现细胞之间的信号交流。小分子肽是重要的胞间信号感应分子,在植物的不同器官组织、发育阶段主要参与调节植物的生长发育过程和应答生物和非生物胁迫的应激反应,以协调和整合细胞功能。该文全面概述了植物小分子肽的发现、结构特点、分类系统及其功能研究进展,并重点对近年来国内外有关翻译后修饰小肽CLE(CLAVATA3/ESR)家族和富含半胱氨酸肽RALF(快速碱化因子)家族的研究进展进行综述,为植物小分子肽的深入研究提供基础信息,并为今后的研究方向提供参考。     

植物类MT与植物络合肽

金属硫蛋白在哺乳动物的解毒方面民挥着重要作用,植物本身也存在类似的解毒机制。研究表明,植物存在基因编码的类ＭＴ,另外还有非基因编码的植物ＭＴ,又称植物络合肽,类ＭＴ在必需重金属离子（例如Ｚｎ＾２＋、Ｃｕ＾２＋）的代谢中挥着重要作用而植物络合肽在非必需重金属离子（例如Ｃｄ＾２＋）的解毒中起到关键作用。本文了类ＭＴ和植物络合肽之间的关系以及各自的生物合成途径、相关的结构与功能、在植物中的分布等。     

Expression of the early nodulin, ENOD40, in soybean roots in response to various lipo-chitin signal molecules

The lipo-chitin (LCO) nodulation signal (nod signal) purified from Bradyrhizobium japonicum induced nodule primordia on soybean (i.e. Glycine soja) roots. These primordia were characterized by a bifurcated vascular connection, cortical cell division, and the accumulation of mRNA of the early nodulin gene, ENOD40. A chemically synthesized LCO identical in structure to the Nod signal purified from B. japonicum cultures showed the same activity when inoculated on to soybean roots. Surprisingly, synthetic LCO or chitin pentamer, inactive in inducing root hair curling (HAD) or cortical cell division (NOI) in G. soja, induced the transient accumulation of ENOD40 mRNA. In roots inoculated with such LCO, ENOD40 mRNA was abundant at 40 h after inoculation but decreased to the background levels 6 days after inoculation. In contrast, nod signals active in inducing HAD and NOI induced high levels of ENOD40 accumulation at 40 h and 6 days after inoculation. In situ hybridization analysis showed that ENOD40 mRNA accumulated in the pericycle of the vascular bundle at 24 h after root inoculation with nod signal. At 6 days post-inoculation with nod signal, ENOD40 expression was seen in dividing subepidermal cortical cells. These results provide morphological and molecular evidence that nodule induction in soybean in response to purified or synthetic nod signal is similar, if not identical, to nodule formation induced by bacterial inoculation. Surprisingly, ENOD40 mRNA accumulation occurs in response to non-specific chitin signals. This suggests that, in the case of ENOD40, nodulation specificity is not determined at the level of initial gene expression.     

ENOD40 affects elongation growth in tobacco Bright Yellow-2 cells by alteration of ethylene biosynthesis kinetics

Plant developmental processes are controlled by co-ordinated action of phytohormones and plant genes encoding components of developmental response pathways. ENOD40 was identified as a candidate for such a plant factor with a regulatory role during nodulation. Although its mode of action is poorly understood, several lines of evidence suggest interaction with phytohormone response pathways. This hypothesis was investigated by analysing cytokinin-, auxin-, and ethylene-induced responses on cell growth and cell division in transgenic 35S:NtENOD40 Bright Yellow-2 (BY-2) tobacco cell suspensions. It was found that cell division frequency is controlled by the balance between cytokinin and auxin in wild-type cells and that this regulation is not affected in 35S:NtENOD40 lines. Elongation growth, on the other hand, is reduced upon overexpression of NtENOD40. Analysis of ethylene homeostasis shows that ethylene accumulation is accelerated in 35S:NtENOD40 lines. ENOD40 action can be counteracted by an ethylene perception blocker, indicating that ethylene is a negative regulator of elongation growth in 35S:NtENOD40 cells, and that the NtENOD40-induced response is mediated by alteration of ethylene biosynthesis kinetics.     

Comparison of nodule induction in legume and actinorhizal symbioses: the induction of actinorhizal nodules does not involve ENOD40

Two types of root nodule symbioses are known for higher plants, legume and actinorhizal symbioses. In legume symbioses, bacterial signal factors induce the expression of ENOD40 genes. We isolated an ENOD40 promoter from an actinorhizal plant, Casuarina glauca, and compared its expression pattern in a legume (Lotus japonicus) and an actinorhizal plant (Allocasuarina verticillata) with that of an ENOD40 promoter from the legume soybean (GmENOD40-2). In the actinorhizal Allocasuarina sp., CgENOD40-GUS and GmENOD40-2-GUS showed similar expression patterns in both vegetative and symbiotic development, and neither promoter was active during nodule induction. The nonsymbiotic expression pattern of CgENOD40-GUS in the legume genus Lotus resembled the nonsymbiotic expression patterns of legume ENOD40 genes; however, in contrast to GmENOD40-2-GUS, CgENOD40-GUS was not active during nodule induction. The fact that only legume, not actinorhizal, ENOD40 genes are induced during legume nodule induction can be linked to the phloem unloading mechanisms established in the zones of nodule induction in the roots of both types of host plants.     

Temporal and spatial order of events during the induction of cortical cell divisions in white clover by Rhizobium leguminosarum bv. trifolii inoculation or localized cytokinin addition

We examined the timing and location of several early root responses to Rhizobium leguminosarum bv. trifolii infection, compared with a localized addition of cytokinin in white clover, to study the role of cytokinin in early signaling during nodule initiation. Induction of ENOD40 expression by either rhizobia or cytokinin was similar in timing and location and occurred in nodule progenitor cells in the inner cortex. Inoculation of rhizobia in the mature root failed to induce ENOD40 expression and cortical cell divisions (ccd). Nitrate addition at levels repressing nodule formation inhibited ENOD40 induction by rhizobia but not by cytokinin. ENOD40 expression was not induced by auxin, an auxin transport inhibitor, or an ethylene precursor. In contrast to rhizobia, cytokinin addition was not sufficient to induce a modulation of the auxin flow, the induction of specific chalcone synthase genes, and the accumulation of fluorescent compounds associated with nodule initiation. However, cytokinin addition was sufficient for the localized induction of auxin-induced GH3 gene expression and the initiation of ccd. Our results suggest that rhizobia induce cytokinin-mediated events in parallel to changes in auxin-related responses during nodule initiation and support a role of ENOD40 in regulating ccd. We propose a model for the interactions of cytokinin with auxin, ENOD40, flavonoids, and nitrate during nodulation.