Glutathione in plants: an integrated overview

Plants cannot survive without glutathione (γ-glutamylcysteinylglycine) or γ-glutamylcysteine-containing homologues. The reasons why this small molecule is indispensable are not fully understood, but it can be inferred that glutathione has functions in plant development that cannot be performed by other thiols or antioxidants. The known functions of glutathione include roles in biosynthetic pathways, detoxification, antioxidant biochemistry and redox homeostasis. Glutathione can interact in multiple ways with proteins through thiol-disulphide exchange and related processes. Its strategic position between oxidants such as reactive oxygen species and cellular reductants makes the glutathione system perfectly configured for signalling functions. Recent years have witnessed considerable progress in understanding glutathione synthesis, degradation and transport, particularly in relation to cellular redox homeostasis and related signalling under optimal and stress conditions. Here we outline the key recent advances and discuss how alterations in glutathione status, such as those observed during stress, may participate in signal transduction cascades. The discussion highlights some of the issues surrounding the regulation of glutathione contents, the control of glutathione redox potential, and how the functions of glutathione and other thiols are integrated to fine-tune photorespiratory and respiratory metabolism and to modulate phytohormone signalling pathways through appropriate modification of sensitive protein cysteine residues.     

Apomixis in flowering plants: an overview

Apomixis is a common feature of perennial plants, which occurs in ca. 60% of the British flora, but has been largely ignored by reproductive theoreticians. Successful individuals may cover huge areas, and live to great ages, favoured by 'symmetrical' selection. Apomixis is favoured by colonizing modes, for instance post-glacially. Despite its theoretical advantages, apomixis usually coexists with sexuality, suggesting 'hidden' disadvantages. Agamospermy (apomixis by seed) is relatively uncommon, but gains from the attributes of the seed. It pays agamospermy genes, which discourage recombination, to form co-adapted linkage groups, so that they become targets for disadvantageous recessive mutant accumulation. Consequently, agamospermy genes cannot succeed in diploids and agamosperms are hybrid and highly heterotic. Agamospermous endosperm may suffer from genomic imbalance, so that nutritious ovules, which can support embryos without endosperm, may be preadapted for agamospermy. When primary endosperm nucleus fertilization ('pseudogamy') continues as a requirement for many aposporous agamosperms, selfing sex becomes preadaptive and archesporial sex remains an option. Apomictic populations can be quite variable although apomictic families are much less variable than sexuals. Only in some diplosporous species does sex disappear completely, and in those species some release of variability may persist through somatic recombination. The search for an agamospermy gene suitable for genetic modification should target fertile sexuals with a single localized agamospermy (A) gene, which therefore lack a genetic load. The A gene should coexist alongside sexuality, so that it would be easy to select seedlings of sexual and asexual origins. Plants with sporophytic agamospermy provide all these attributes.     

Sectoriality and physiological organisation in herbaceous plants: an overview

The physiological organisation of plants is considered in relation to the carbon economy of plant parts. Although assimilate is partitioned according to the relative strength of sinks, in many species there is also a very close relationship between partitioning and shoot phyllotaxy, giving rise to sectorial patterns of allocation whereby only certain sinks are supported by any source leaf. Essentially these sinks are in the same orthostichy as the source leaf. This constraint of the vascular architecture on assimilate distribution to developing sinks such as leaves, flowers and fruits is not always absolute, as following the loss of their principal source leaves these sinks can in many cases be supplied with assimilate by other leaves via new inter-orthostichy pathways. The supply of assimilate to major sinks such as developing fruits becomes more and more localised with time so that a fruit in an axillary position becomes largely supported by its subtending leaf; the reproductive node—a metamer-can thus be regarded as a relatively autonomous unit of the plant (an IPU). Similary, once established after a developmental phase of assimilate import, tiller ramets and branches in unitary plants tend to become physiologically autonomous modules. However, the functional autonomy of tillers is reversed following defoliation or shading as they are then sustained by the import of assimilate, subject to its availability, from unaffected tillers. Consequently the plant becomes physiologically integrated by the flow of assimilate from one part to another. The mainly autonomous ramets of many stoloniferous and rhizomatous species display a similar pattern of physiological integration in response to source manipulation, but in some species the ramets appear to maintain their independent functioning as a normal feature of the carbon allocation within the clone. In other clonal species, as the clone develops and becomes more structurally complex, vascular constraints start to restrict the movement of resources, and the clone becomes composed of a number of semi-autonomous IPUs. In unitary plants branches appear to remain very physiologically isolated in terms of their carbon economy once they become established, irrespective of a range of source-sink manipulations.These different patterns of physiological integration and organisation are discussed in relation to different strategies of assimilate utilisation and conservation.     

Transport genes of Chromobacterium violaceum: an overview

The complete genome sequence of the free-living bacterium Chromobacterium violaceum has been determined by a consortium of laboratories in Brazil. Almost 500 open reading frames (ORFs) coding for transport-related membrane proteins were identified in C. violaceum, which represents 11% of all genes found. The main class of transporter proteins is the primary active transporters (212 ORFs), followed by electrochemical potential-driven transporters (154 ORFs) and channels/pores (62 ORFs). Other classes (61 ORFs) include group translocators, transport electron carriers, accessory factors, and incompletely characterized systems. Therefore, all major categories of transport-related membrane proteins currently recognized in the Transport Protein Database (http://tcdb.ucsd.edu/tcdb) are present in C. violaceum. The complex apparatus of transporters of C. violaceum is certainly an important factor that makes this bacterium a dominant microorganism in a variety of ecosystems in tropical and subtropical regions. From a biotechnological point of view, the most important finding is the transporters of heavy metals, which could lead to the exploitation of C. violaceum for bioremediation.     

Antisense RNA in transgenic plants

The data on the effects of antisense RNA in plants is reviewed. Results of expression of the genes for selective markers, antisense reporter genes, functioning and viral genes are analyzed. The molecular mechanisms for inhibiting effects of antisense RNA and the potential use of the phenomenon in the plants biotechnology are discussed. The formation of long duplexes between the antisense RNA and messenger RNA are supposed to be irrelevant to suppression of gene expression in plants by the antisense RNA.     

Physiological changes induced by chromium stress in plants: an overview

This article presents an overview of the mechanism of chromium (Cr) stress in plants. Toxic effects of Cr on plant growth and development depend primarily on its valence state. Cr(VI) is highly toxic and mobile whereas Cr(III) is less toxic. Cr-induced oxidative stress involves induction of lipid peroxidation in plants that cause severe damage to cell membranes which includes degradation of photosynthetic pigments causing deterioration in growth. The potential of plants with the adequacy to accumulate or to stabilize Cr compounds for bioremediation of Cr contamination has gained engrossment in recent years.     

Matrix metalloproteinases in plants: a brief overview

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases belonging to the metzincin clan. MMPs have been characterized in detail in mammals, and they have been shown to play key roles in many physiological and pathological processes. Plant MMP-like proteases exist, but relatively few have been characterized. It has been speculated that plant MMPs are involved in remodeling of the plant extracellular matrix during growth, development and stress response. However, the precise functions and physiological substrates in higher plants remain to be determined. In this brief overview, we summarize the current knowledge of MMPs in higher plants and algae.     

Production of vaccines and therapeutic antibodies for veterinary applications in transgenic plants: an overview

During the past two decades, antibodies, antibody derivatives and vaccines have been developed for therapeutic and diagnostic applications in human and veterinary medicine. Numerous species of dicot and monocot plants have been genetically modified to produce antibodies or vaccines, and a number of diverse transformation methods and strategies to enhance the accumulation of the pharmaceutical proteins are now available. Veterinary applications are the specific focus of this article, in particular for pathogenic viruses, bacteria and eukaryotic parasites. We focus on the advantages and remaining challenges of plant-based therapeutic proteins for veterinary applications with emphasis on expression platforms, technologies and economic considerations.     

Antisense chalcone synthase genes in petunia: Visualization of variable transgene expression

Summary The constitutive expression of an antisense chalcone synthase (CHS) gene in transgenic petunia plants results with high frequency in a reduced flower pigmentation due to a reduction in the CHS mRNA steady-state level in floral tissue. Here we show that this reduction is specific for CHS mRNA; chalcone flavanone isomerase (CHI) and dihydroflavonol reductase (DFR) mRNA steady-state levels are unaffected. However, in white floral tissue a severe reduction in CHI specific activity is found, accompanied by an altered signal for CHI protein on western blots. We find no correlation between the phenotypic effect of the antisense CHS gene and its chromosomal position. For some of the antisense CHS transformants the flower phenotype is highly variable. We demonstrate that pigmentation in these plants can be influenced by gibberellic acid and light, suggesting that the variable flower phenotype is caused by changes in physiological conditions during flower development. The results not only indicate that flower pigmentation in these plants reveals the variable expression of the antisense transgene, but also show that genomic sequences flanking the transgene may render its expression extremely susceptible to physiological conditions.     

Gene expression studies of reference genes for quantitative real-time PCR: an overview in insects

Whenever gene expression is being examined, it is essential that a normalization process is carried out to eliminate non-biological variations. The use of reference genes, such as glyceraldehyde-3-phosphate dehydrogenase, actin, and ribosomal protein genes, is the usual method of choice for normalizing gene expression. Although reference genes are used to normalize target gene expression, a major problem is that the stability of these genes differs among tissues, developmental stages, species, and responses to abiotic factors. Therefore, the use and validation of multiple reference genes are required. This review discusses the reasons that why RT-qPCR has become the preferred method for validating results of gene expression profiles, the use of specific and non-specific dyes and the importance of use of primers and probes for qPCR as well as to discuss several statistical algorithms developed to help the validation of potential reference genes. The conflicts arising in the use of classical reference genes in gene normalization and their replacement with novel references are also discussed by citing the high stability and low stability of classical and novel reference genes under various biotic and abiotic experimental conditions by employing various methods applied for the reference genes amplification.     

Speciation genes in plants

Background

Analyses of speciation genes – genes that contribute to the cessation of gene flow between populations – can offer clues regarding the ecological settings, evolutionary forces and molecular mechanisms that drive the divergence of populations and species. This review discusses the identities and attributes of genes that contribute to reproductive isolation (RI) in plants, compares them with animal speciation genes and investigates what these genes can tell us about speciation.

Scope

Forty-one candidate speciation genes were identified in the plant literature. Of these, seven contributed to pre-pollination RI, one to post-pollination, prezygotic RI, eight to hybrid inviability, and 25 to hybrid sterility. Genes, gene families and genetic pathways that were frequently found to underlie the evolution of RI in different plant groups include the anthocyanin pathway and its regulators (pollinator isolation), S RNase-SI genes (unilateral incompatibility), disease resistance genes (hybrid necrosis), chimeric mitochondrial genes (cytoplasmic male sterility), and pentatricopeptide repeat family genes (cytoplasmic male sterility).

Conclusions

The most surprising conclusion from this review is that identities of genes underlying both prezygotic and postzygotic RI are often predictable in a broad sense from the phenotype of the reproductive barrier. Regulatory changes (both cis and trans) dominate the evolution of pre-pollination RI in plants, whereas a mix of regulatory mutations and changes in protein-coding genes underlie intrinsic postzygotic barriers. Also, loss-of-function mutations and copy number variation frequently contribute to RI. Although direct evidence of positive selection on speciation genes is surprisingly scarce in plants, analyses of gene family evolution, along with theoretical considerations, imply an important role for diversifying selection and genetic conflict in the evolution of RI. Unlike in animals, however, most candidate speciation genes in plants exhibit intraspecific polymorphism, consistent with an important role for stochastic forces and/or balancing selection in development of RI in plants.Key words: Speciation, reproductive isolation, mating system isolation, pollinator isolation, ecological isolation, unilateral incompatibility, hybrid necrosis, hybrid sterility, hybrid inviability, hybrid breakdown, cytoplasmic male sterility, restoration     

植物印迹基因研究进展

印迹基因的表达受表观机制调控,依据其亲本来源在植物胚乳中表现为单等位基因表达的特殊模式。这些基因在调控胚及其附属结构的发育、控制种子的大小、生殖隔离以及防止无性生殖上发挥着关键作用。随着植物表观遗传学研究的不断深入,目前对于印迹基因的探索已逐渐成为表观遗传学研究的热点。文章介绍了关于印迹基因起源的亲本冲突学说,并以拟南芥的MEA、FIS2、FWA、MPC、PHE1,玉米的FIE1、FIE2等重要印迹基因为例,阐述了有关植物印迹基因的表达调控机制及最新研究进展。     

Calmodulin: an overview

Calmodulin is a 16,700-dalton Ca2+-binding protein ubiquitous in the eukaryotes. It has no intrinsic enzymatic activity, but it regulates a wide spectrum of enzymes that control many basic cellular processes, ranging from the metabolism of cyclic nucleotides, Ca2+, and glycogen to contractile activity and stimulus-secretion coupling. Mounting evidence now indicates that calmodulin is the major intracellular Ca2+ receptor that remained elusive despite three decades of extensive work by many investigators.     

Hantaviruses: an overview

Hantaviruses are a newly emerging group of rodent-borne viruses that have significant zoonotic potential. Human infection by hantaviruses can result in profound morbidity and mortality, with death rates as high as 50%, and potentially long-term cardiovascular consequences. Hantaviruses are carried by peridomestic and wild rodents worldwide and have occasionally been linked to infections in laboratory rodents. Because these viruses have been associated with significant human disease, they have become the subject of intense scientific investigation. In this review the reader is introduced to the hantaviruses, including hantavirus diseases and their pathogenesis. A review of the biology, morphology, and molecular biology of the hantaviruses with a brief overview of the ecology and biology of hantavirus-rodent pairs is also included. The risks of occupational exposure to hantaviruses, diagnosis of hantavirus infections, and methods for handling potentially infected rodents and tissues are discussed as well.