The response of tobacco (Nicotiana tabacum L. cv Xanthi-nc) plants with elevated catalase activity was studied after infection by tobacco mosaic virus (TMV). These plants contain the yeast (Saccharomyces cerevisiae) peroxisomal catalase gene CTA1 under the control of the cauliflower mosaic virus 35S promoter. The transgenic lines exhibited 2-to 4-fold higher total in vitro catalase activity than untransformed control plants under normal growth conditions. Cellular localization of the CTA1 protein was established using immunocytochemical analysis. Gold particles were detected mainly inside peroxisomes, whereas no significant labeling was detected in other cellular compartments or in the intercellular space. The physiological state of the transgenic plants was evaluated in respect to growth rate, general appearance, carbohydrate content, and dry weight. No significant differences were recorded in comparison with non-transgenic tobacco plants. The 3,3Ј-diaminobenzidine-stain method was applied to visualize hydrogen peroxide (H 2 O 2 ) in the TMV infected tissue. Presence of H 2 O 2 could be detected around necrotic lesions caused by TMV infection in non-transgenic plants but to a much lesser extent in the CTA1 transgenic plants. In addition, the size of necrotic lesions was significantly bigger in the infected leaves of the transgenic plants. Changes in the distribution of H 2 O 2 and in lesion formation were not reflected by changes in salicylic acid production. In contrast to the local response, the systemic response in upper noninoculated leaves of both CTA1 transgenic and control plants was similar. This suggests that increased cellular catalase activity influences local but not systemic response to TMV infection.Reactive oxygen species (ROS), such as ⅐ O 2 , hydrogen peroxide (H 2 O 2 ), and ⅐ OH, are associated with a number of physiological disorders in plants (Inzé and Van Montagu, 1995). Although ROS are produced as a product of normal cell metabolism, their levels are enhanced by exposure to biotic and abiotic stresses. It has been demonstrated that ROS, including H 2 O 2 , are a critical factor in the sequence of events taking place on the onset of infection, leading in many cases to hypersensitive response (HR) and the activation of the pathogenesis-related genes (PR), as well as in other processes associated with response to infection (for reviews, see Bolwell et al., 1995). The rapid generation of ROS as a result of pathogen attack is referred to as oxidative burst. A growing body of evidence suggests that this process is mediated by a membrane-bound NAD(P)H oxidase that resembles the phagocyte enzyme (Scheel, 2001). As the first step, the enzyme forms superoxide radicals, which are then converted to oxygen and hydrogen peroxide either spontaneously or by an extracellular superoxide dismutase. As an alternative, the contribution of other enzymes to the oxidative burst, like peroxidase, amine oxidase, or oxalate oxidase, is postulated (Bolwell et al., 1995; Allan and Fluhr, 1997; Zhou et al., 1998). ...
The ornithine transaminase (otaA) gene of Aspergillus nidulans has been cloned by transformation of the A. nidulans pro-ota- mutant strain with a cosmid gene library. The otaA gene contains two introns and potentially codes for a 453-aa-long protein. The deduced amino-acid sequence is homologous to known ornithine transaminases from Saccharomyces cerevisiae, Plasmodium falciparum, Vigna aconitifolia, rat, mouse and man, particularly in the pyridoxal phosphate-binding domain. The expression of the otaA gene is specifically induced by arginine, and is also under the control of nitrogen-metabolite and carbon-catabolite repression. Regulation of the gene occurs at both transcriptional and post-transcriptional levels. The promoter region of otaA contains putative AREA and CREA binding-sites. Fusion proteins containing AREA or CREA DNA-binding domains bind some of these sites. CREA binding-sites correspond very well to the CREA-binding consensus sequence which is SYGGRG. AREA binding-sites are composed of GATT sequences which are not typical binding sites for the GATA - binding family of transcription factors.
A random amplified polymorphic DNA marker OPG17450 linked to the Ns gene that confers resistance of potato to potato virus S (PVS), was used to develop sequence‐characterized amplified region (SCAR) markers. After cloning and sequencing of OPG17450 new polymerase chain reaction (PCR) primers were designed to generate dominant (SCG17321) and codominant (SCG17448) markers. For SCG17448, polymorphism between susceptible and resistant genotypes was recovered after digestion of the marker with the restriction enzyme Muni. In addition to the band corresponding to ‘susceptible’ allele that does not contain the Muni cleavage site, two bands of approximately 251 bp and 197 bp were observed in the resistant genotypes. The usefulness of these SCAR markers was verified in diploid potatoes possessing the Ns locus from clone G‐LKS 678147/60, and in tetraploid potatoes derived from G‐LKS 678147/60 and from clone MPI 65118/3.
Soybean β-1,3-endoglucanase represents a model system for studies on early plant responses to infection by fungal pathogens, and it has been implicated in the release of elicitors from fungal cell walls. In the present study, potato plants were transformed with the soybean β-1,3-endoglucanase cDNA via Agrobacterium delivery system. The transfer of the gene into potato genome was confirmed by (i) PCR amplification, (ii) Northern blot analyses, and (Hi) an increase in the activity of β-1,3-endoglucanase in transgenic plants. The transformation resulted in an increased resistance of selected transgenic plants to infection by Phytophthora infestans, an important pathogen.
Previous studies argue that salicylic acid (SA) plays an important role in the plant signal transduction pathway(s) leading to disease resistmace. It has been proposed that one of its modes of action is inhibition of eatalase and elevation of H202 level in the tissue. To verify the role of SA and I-[202 during pathogenesis, transgenic tobacco plants expressing Saccharomyces cerevisiae CTA1 gene coding for peroxisomat eatalase were construtted. These plants possess 2-4-fold higher total catalase activity under normal growth conditions. No symptoms of chlorosis and/or necrosis were observed. Levels of pathogenesisrelated proteins (PR) and their respective mRNAs were significantly rednced in the ixffected leaves of the transgenic plants. No change in PR expression was detected in uninfected leaves of both CTA1 and control plants challenged with TMV.These results suggest that elevation in catalase activity and resulting reduction of H202 level restdts in more severe local disease symptoms, apparently due to alteration of the hypersensitive response mechanism and does not influence systemic acquired resistance after viral infection.
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