24-Epibrasinolide Delays Chlorophyll Degradation and Stimulates the Photosynthetic Machinery in Magnesium-Stressed Soybean Plants

Adverse effects caused by inadequate magnesium (Mg) supply (deficiency or excess) often cause oxidative stress in chloroplasts and a decline in photosynthetic activity. However, 24-epibrassinolide (EBR) is a natural, biodegradable, and ecologically viable plant growth regulator with multiple roles in plant metabolism. This research aims to determine whether the foliar application of EBR (1) can delay chlorophyll degradation and/or (2) mitigate oxidative stress on the photosynthetic process in magnesium-stressed soybean plants. The experiment followed a completely randomized factorial design with two concentrations of 24-epibrassinolide (0 and 0.1 mM EBR, described as – EBR and?+?EBR, respectively) and three Mg supplies (0.0225, 2.25 and 225 mM Mg, described as low, control and high supply of Mg). Inadequate Mg supplies (deficiency and excess) negatively interfered with photosynthetic pigments, chlorophyll fluorescence and gas exchange. However, exogenous EBR sprayed in plants under high Mg maximized superoxide dismutase (37%), catalase (34%), ascorbate peroxidase (48%) and peroxidase (49%), protecting against oxidative stress and delaying chlorophyll degradation. Concomitantly, plants sprayed with this steroid had increases in Mg content, improving the photochemical efficiency and gas exchange because Mg plays an essential role during the light capture process.

     

植物叶绿素的降解

简要介绍了植物叶绿素降解及其机制的研究进展。     

Degradation of mRNA in Escherichia coli

Degradation of messenger RNAs (mRNAs) is a universal process that occurs in every cell and has important implications for nucleotide metabolism and gene expression. One organism in which mRNA degradation has been thoroughly studied is the bacterium Escherichia coli (E. coli). In this review I describe what is presently known about the different processes involved in the conversion of mRNAs from high molecular weight species to mononucleotides in E. coli. The ribonucleases and accessory factors involved in mRNA degradation, and features on mRNAs that make them resistant or sensitive to degradation will also be described. At the conclusion of this review, some of the anticipated directions of future research on this topic will be discussed.     

细菌mRNA的降解机制

在细菌中,mRNA降解具有重要的意义,它不仅可以再循环核苷酸,而且还可以根据生长条件的变化调控基因表达.细菌mRNA的降解机制可以分为3种：① mRNA的一般降解途径|② mRNA的质量控制途径|③ 小RNA介导的降解途径. 这些途径有些与真核生物的mRNA降解途径存在很大差异,有些在真核生物中消失了. 另外,mRNA降解途径还可以直接调控细菌致病因子的表达,这使得细菌mRNA的降解途径很有希望成为药物研发的新靶标,或疫苗制备的新平台,以应对越来越严重的细菌耐药性问题.本文综述了细菌mRNA的降解机制,并对其应用前景进行了展望.     

真核细胞中mRNA的降解机制

细胞中不同的mRNA半寿期差异很大,mRNA的稳定性受到多种因素的影响,现在已经发现了许多对mRNA的稳定性有影响的顺式因子和反式因子。大量的研究证明在真核细胞内存在复杂的机制调节mRNA的稳定与降解及其所引起的基因表达。现在可以肯定在真核细胞中至少存在着三种mRNA的降解方式：依赖于脱腺苷酸的降解,无义密码介导的mRNA的降解和核酸内切酶的水解。其中依赖于脱腺苷酸的降解方式是细胞内大多数mRNA降解的主要途径。 Abstract　The half-lives of different mRNAs in Eukaryotic cells vary greatly. There are many elements can influence mRNA stability, including cis-acting factors and trans-acting factors. Evidences show that there exist complicated mechanisms in cells that regulate mRNA stability, degradation and expression. Recent results have defined three mRNA degradation pathways in Eukaryotic cells: deadenylation-dependent mRNA decay, nonsense-mediated mRNA decay and endonuclolytic cleavage. Among these pathways deadenylation-dependent decay is the most general pathway.     

真核细胞中mRNA的降解机制

细胞中不同的ｍ ＲＮＡ 半寿期差异很大,ｍ ＲＮＡ 的稳定性受到多种因素的影响,现在已经发现了许多对ｍ ＲＮＡ 的稳定性有影响的顺式因子和反式因子。大量的研究证明在真核细胞内存在复杂的机制调节ｍ ＲＮＡ 的稳定与降解及其所引起的基因表达。现在可以肯定在真核细胞中至少存在着三种ｍ ＲＮＡ的降解方式：依赖于脱腺苷酸的降解,无义密码介导的ｍ ＲＮＡ 的降解和核酸内切酶的水解。其中依赖于脱腺苷酸的降解方式是细胞内大多数ｍ ＲＮＡ 降解的主要途径。     

Assaying Proteasomal Degradation in a Cell-free System in Plants

The ubiquitin-proteasome pathway for protein degradation has emerged as one of the most important mechanisms for regulation of a wide spectrum of cellular functions in virtually all eukaryotic organisms. Specifically, in plants, the ubiquitin/26S proteasome system (UPS) regulates protein degradation and contributes significantly to development of a wide range of processes, including immune response, development and programmed cell death. Moreover, increasing evidence suggests that numerous plant pathogens, such as Agrobacterium, exploit the host UPS for efficient infection, emphasizing the importance of UPS in plant-pathogen interactions.The substrate specificity of UPS is achieved by the E3 ubiquitin ligase that acts in concert with the E1 and E2 ligases to recognize and mark specific protein molecules destined for degradation by attaching to them chains of ubiquitin molecules. One class of the E3 ligases is the SCF (Skp1/Cullin/F-box protein) complex, which specifically recognizes the UPS substrates and targets them for ubiquitination via its F-box protein component. To investigate a potential role of UPS in a biological process of interest, it is important to devise a simple and reliable assay for UPS-mediated protein degradation. Here, we describe one such assay using a plant cell-free system. This assay can be adapted for studies of the roles of regulated protein degradation in diverse cellular processes, with a special focus on the F-box protein-substrate interactions.     

mRNA差异显示技术及其在园艺植物上的应用（综述）

mRNA差异显示技术是鉴别基因差异表达方法之一,已在生物技术相关领域中广泛应用.本文介绍mRNA差异显示技术的基本原理及主要优缺点,较详细地综述了该技术在园艺植物生物技术方面的最新应用状况及取得的研究结果.     

MicroRNA引起mRNA降解关键核酸酶CAF1和POP2的生物进化分析

MicroRNA(miRNA)参与调控高等真核生物中三分之一以上基因的表达,其中核酸酶CAF1(CCR4-associated factor 1)及其同源基因POP2在miRNA引发的mRNA 3′端多聚腺苷酸(poly(A))的脱腺苷酸化过程中起了关键作用.通过实时定量RT-PCR的方法检测了小鼠各个组织中CAF1和POP2的相对表达情况,发现CAF1和POP2的组织分布特征不同.大多数组织中CAF1的表达水平明显高于POP2,并且组织间差异很大,特别是在大脑、小脑以及睾丸组织中CAF1的表达量很高,而POP2的表达量和变化幅度都较低.蛋白质序列比对发现,CAF1和POP2是一类进化过程中高度保守的核酸外切酶,在酵母、线虫、果蝇和尾索动物代表物种海鞘中都只存在单一基因,而进化到鱼类后产生了两个同源基因——CAF1和POP2,其中CAF1的氨基酸序列保守性较POP2更高,更加接近于原始的单一序列.CAF1和POP2这一对同源基因氨基酸序列的主要差别在蛋白质的C端.鱼类中POP2的C端序列同CAF1的序列较为接近,而在爬行动物之后POP2产生了与CAF1具有明显差异的C端序列,并逐渐趋于稳定.我们的分析结果同已有的功能研究一致,表明可能在miRNA产生后的进化过程中产生了CAF1和POP2两个同源基因,其中CAF1主要担负miRNA调控mRNA脱腺苷酸化的功能,而POP2可能主要参与其它不同的调控作用。     

转基因植物对有机污染物的吸收、转化和降解

有机污染物是土壤、水体和大气环境的重要污染物.利用和加强植物修复作用是控制环境污染的有效途径.近年来,一些具有修复功能的外源基因被陆续引入到植物中,使转基因植物的生物修复能力大大增强.文章介绍了植物对污染环境中有机污染物,尤其是持久性有机污染物(POPs)的吸收、转化和降解作用,阐述了转基因植物用于被污染环境修复方面的研究进展和应用前景.     

The Mitochondrial Protein Import Machinery of Plants (MPIMP) database

The Mitochondrial Protein Import Machinery of Plants database (MPIMP) is an Internet-accessible database containing detailed information on the protein import apparatus of plant mitochondria. The Arabidopsis genome was searched for com-ponents of the mitochondrial protein import apparatus using components from the well-characterized model system of Saccharomyces cerevisiae. Twenty six homologues of 34 components could be found, encompassing the essential components for the general and carrier import pathways. The database is available through the Internet at http://millar3.biochem.uwa.edu.au/~lister/index.html.     

Delineating Calcium Signaling Machinery in Plants: Tapping the Potential through Functional Genomics

Plants have developed calcium (Ca²⁺) signaling as an important mechanism of  regulation of  stress perception,  developmental cues, and  responsive gene  expression. The  post-genomic era has witnessed the successful unravelling of the functional characterization of genes and the creation of large datasets of molecular information. The major elements of Ca²⁺ signaling machinery include Ca²⁺ sensors and responders such as Calmodulins (CaMs), Calmodulin-like proteins (CMLs), Ca²⁺/CaM-dependent protein kinases (CCaMKs), Ca²⁺-dependent protein kinases (CDPKs), Calcineurin B-like proteins (CBLs) as well as transporters, such as Cyclic nucleotide-gated channels (CNGCs), Glutamate-like receptors (GLRs), Ca²⁺-ATPases, Ca²⁺/H⁺ exchangers (CAXs) and mechanosensitive channels. These elements play an important role in the regulation of physiological processes and plant responses to various stresses. Detailed genomic analysis can help us in the identification of potential molecular targets that can be exploited towards the development of stress-tolerant crops. The information sourced from model systems through omics approaches helps in the prediction and simulation of regulatory networks involved in responses to different stimuli at the molecular and cellular levels. The molecular delineation of Ca²⁺ signaling pathways could be a stepping stone for engineering climate-resilient crop plants. Here, we review the recent developments in Ca²⁺ signaling in the context of transport, responses, and adaptations significant for crop improvement through functional genomics approaches.