Proteomics applied on plant abiotic stresses: role of heat shock proteins (HSP)

The most crucial function of plant cell is to respond against stress induced for self-defence. This defence is brought about by alteration in the pattern of gene expression: qualitative and quantitative changes in proteins are the result, leading to modulation of certain metabolic and defensive pathways. Abiotic stresses usually cause protein dysfunction. They have an ability to alter the levels of a number of proteins which may be soluble or structural in nature. Nowadays, in higher plants high-throughput protein identification has been made possible along with improved protein extraction, purification protocols and the development of genomic sequence databases for peptide mass matches. Thus, recent proteome analysis performed in the vegetal Kingdom has provided new dimensions to assess the changes in protein types and their expression levels under abiotic stress. As reported in this review, specific and novel proteins, protein-protein interactions and post-translational modifications have been identified, which play a role in signal transduction, anti-oxidative defence, anti-freezing, heat shock, metal binding etc. However, beside specific proteins production, plants respond to various stresses in a similar manner by producing heat shock proteins (HSPs), indicating a similarity in the plant's adaptive mechanisms; in plants, more than in animals, HSPs protect cells against many stresses. A relationship between ROS and HSP also seems to exist, corroborating the hypothesis that during the course of evolution, plants were able to achieve a high degree of control over ROS toxicity and are now using ROS as signalling molecules to induce HSPs.     

Response to cadmium in higher plants

The paper summarizes present knowledge in the field of higher plant responses to cadmium, an important environmental pollutant. The principal mechanisms reviewed here include phytochelatin-based sequestration and compartmentalization processes, as well as additional defense mechanisms, based on cell wall immobilization, plasma membrane exclusion, stress proteins, stress ethylene, peroxidases, metallothioneins, etc. An analysis of data taken from the international literature has been carried out, in order to highlight possible ‘qualitative’ and ‘quantitative’ differences in the response of wild-type (non-tolerant) plants to chronic and acute cadmium stress. The dose-response relationships indicate that plant response to low and high cadmium level exposures is a very complex phenomenon indeed: cadmium evokes a number of parallel and/or consecutive events at molecular, physiological and morphological levels. We propose that, above all in response to acute cadmium stress, various mechanisms might operate both in an additive and in a potentiating way. Thus, a holistic and integrated approach seems to be necessary in the study of the response of higher plants to cadmium. This multi-component model, which we would call ‘fan-shaped’ response, may accord with the Selyean ‘general adaptation syndrome’ hypothesis. While cadmium detoxification is a complex phenomenon, probably under polygenic control, cadmium ‘real’ tolerance—found in mine plants or in plant systems artificially grown under long-term selection pressure, exposed to high levels of cadmium—seems to be a simpler phenomenon, possibly involving only monogenic/oligogenic control. We conclude that, following a ‘pyramidal’ model, (adaptive) tolerance is supported by (constitutive) detoxification mechanisms, which in turn rely on (constitutive) homeostatic processes. The shift between homeostasis and ‘fan-shaped’ response can be rapid and involve quick changes in (poly)gene expression. Differently, the slow shift from ‘fan-shaped’ response to ‘real’ cadmium tolerance is caused and affected by long-term selection pressure, which may increase the frequency (and promote the expression) of one or a few tolerance gene(s).     

Proteomic analysis of differentially expressed proteins in fungal elicitor-treated Arabidopsis cell cultures

Slow progress has been made in discovering plant genes governing the interaction of plant pathogens and their hosts using classical genetic approaches. Extensive studies employing DNA microarray techniques to identify global changes in gene expression during pathogen-host interaction have greatly enhanced discovery of genetic components regulating the plant defence response to pathogen attack. In this study, a complementary approach was used to identify changes in protein abundance during interaction of Arabidopsis cell cultures with a pathogen-derived elicitor. The soluble protein fractions were analysed by two-dimensional difference gel electrophoresis and proteins differentially expressed in response to treatment with fungal elicitor were identified via matrix-assisted laser desorption ionization-time of flight mass spectrometry. Elicitor responsive proteins included molecular chaperones, oxidative stress defence proteins, mitochondrial proteins, and enzymes of a diverse number of metabolic pathways. The findings, in combination with currently available microarray data, will form the basis of a filter to identify pivotal genes whose role in pathogen defence systems will require confirmation using gene knockout mutants.     

Isolation and characterisation of cDNA encoding a wheat heavy metal‐associated isoprenylated protein involved in stress responses

In cells, metallochaperones are important proteins that safely transport metal ions. Heavy metal‐associated isoprenylated plant proteins (HIPPs) are metallochaperones that contain a metal binding domain and a CaaX isoprenylation motif at the carboxy‐terminal end. To investigate the roles of wheat heavy metal‐associated isoprenylated plant protein (TaHIPP) genes in plant development and in stress responses, we isolated cDNA encoding the wheat TaHIPP1 gene, which contains a heavy metal‐associated domain, nuclear localisation signals and an isoprenylation motif (CaaX motif). Quantitative real‐time PCR analysis indicated that the TaHIPP1 gene was differentially expressed under biotic and abiotic stresses. Specifically, TaHIPP1 expression was up‐regulated by ABA exposure or wounding. Additionally, TaHIPP1 over‐expression in yeast (Schizosaccharomyces pombe) significantly increased the cell growth rate under Cu²⁺ and high salinity stresses. The nuclear localisation of the protein was confirmed with confocal laser scanning microscopy of epidermal onion cells after particle bombardment with chimeric TaHIPP1‐GFP constructs. In addition, TaHIPP1 was shown to enhance the susceptibility of wheat to Pst as determined by virus‐induced gene silencing. These data indicate that TaHIPP1 is an important component in defence signalling pathways and may play a crucial role in the defence response of wheat to biotic and certain abiotic stresses.     

Acidic stress in bacteria

Information on acidic stress in bacteria, studied not only on the phenomenological, but also molecular and genetic levels, are systematized. Acidic stress in bacteria, appearing as the result of the acidification of the medium, is characterized by many events on the level of gene regulation. An increased expression of some genes and a decreased expression of others result in growth deceleration, quantitative and qualitative changes in the synthesis of proteins. Some of the newly synthesized proteins ensure the survival of bacteria in a medium with higher acidity and their protection from other stresses. The applied importance of acidic stress is relevant to some aspects of biotechnology, immunobiology and medicine.     

Stage-specific gene expression during sexual development in Phytophthora infestans

Eight genes that are upregulated during sexual development in the heterothallic oomycete, Phytophthora infestans, were identified by suppression subtractive hybridization. Two genes showed very low but detectable expression in vegetative hyphae and became induced about 40- to >100-fold early in mating, before gametangial initials appeared. The remaining six loci were not induced until later in mating, coincident with the formation of gametangia and oospores, with induction levels ranging from 60- to >100-fold. Five genes were single copy, and three were members of families. Sequence analysis revealed that the predicted products of three of the genes had similarity to proteins that influence RNA stability, namely a ribonuclease activator, the pumilio family of RNA-binding proteins and RNase H. The products of two other mating-induced genes resembled two types of Phytophthora proteins previously shown to elicit plant defence responses. Each mating-induced gene was also expressed in a self-fertile strain, which was shown to be a heterokaryon. However, quantitative and qualitative differences existed in their expression in normal matings and in the self-fertile heterokaryon. Besides the mating-induced genes, two extrachromosomal RNA elements were identified.