The Rx gene confers resistance to a range of potexviruses in transgenic Nicotiana plants.
ABSTRACT Rx-mediated resistance was analyzed in Rx-expressing transgenic Nicotiana plants. The infection outcome of nine Potato virus X isolates mutated at amino acid positions 121 and 127 of the coat protein (CP) confirmed the key role of these amino acids but provided a more complex picture than previously reported. In particular, in Rx-expressing Nicotiana spp., eliciting activity modulated by amino acid 121 was conditioned by the nature of amino acid 127. These results suggest that the specificity of recognition might be modulated by host factors that are somehow subtly modified between Rx-expressing potato and Rx-expressing transgenic Nicotiana plants. Moreover, the CP of three Potexviruses, Narcissus mosaic virus (NMV), White clover mosaic virus (WClMV), and Cymbidium mosaic virus (CymMV), are all recognized by the Rx-based machinery and able to trigger an Rx-dependant hypersensitive response. A smaller elicitor of 90 amino acids was identified in the CP of NMV and WClMV, which contains the previously identified key positions 121 and 127. This elicitor is only weakly conserved (approximately 40% identity) among the CP of the various recognized viruses, suggesting that the Rx molecular machinery targets a conserved structural element of the Potexvirus CP rather than a conserved amino acid motif.
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ABSTRACT: Alcohol oxidases (Alcohol: O2 Oxidoreductase; EC 1.1.3.x) are flavoenzymes that catalyze the oxidation of alcohols to the corresponding carbonyl compounds with a concomitant release of hydrogen peroxide. Based on substrate specificity, alcohol oxidases may be categorized broadly into four different groups namely, (a) Short chain alcohol oxidase (SCAO) (b) Long chain alcohol oxidase (LCAO) (c) Aromatic alcohol oxidase (AAO) and (d) Secondary alcohol oxidase (SAO). The sources reported for these enzymes are mostly limited to bacteria, yeast, fungi, plant, insect and mollusks. However, the quantum of reports for each category of enzymes considerably varies across these sources. The enzymes belonging to SCAO and LCAO are intracellular in nature whereas, AAO and SAO are mostly secreted to the medium. SCAO and LCAO are invariably reported as multimeric proteins with very high holoenzyme-molecular masses but the molecular characteristics of these enzymes are yet to be clearly elucidated. One of the striking features of the alcohol oxidases that make them distinct from the widely known alcohol dehydrogenase is the avidly bound cofactor to the redox center of these enzymes that obviate the need to supplement cofactor during the catalytic reaction. These flavin-based redox enzymes have gained enormous importance in the development of various industrial processes and products primarily for developing biosensors and production of various industrially useful carbonyl compounds. The present review provides an overview on alcohol oxidases from different categories focusing research on these oxidases during the last decade along with their potential industrial applications.Applied Microbiology and Biotechnology 01/2013; · 3.81 Impact Factor
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ABSTRACT: On infection by pathogens, plants initiate defence responses that are able to curtail infection locally. These responses are mediated either by receptor-like proteins that recognize pathogen-associated molecular patterns or by the protein products of disease resistance (R) genes. At the same time, primary defence responses often result in the generation of signals that induce what is known as systemic acquired resistance (SAR), such that defence responses are enhanced on secondary pathogen challenge in distal tissues. R protein-mediated SAR induction is normally accompanied by a type of programmed cell death known as the hypersensitive response (HR) and, in some instances, cell death alone has been implicated in the induction of SAR. This has raised the question of whether R protein-mediated signalling per se induces SAR or whether SAR is an indirect result of the induction of HR. Using the Rx gene of potato, which confers resistance to Potato Virus X in the absence of cell death, we have shown that the HR is dispensable for R protein-mediated induction of SAR and that Rx-induced SAR is mediated by the same salicylate-dependent pathway induced by other R proteins.Molecular Plant Pathology 01/2010; 11(1):155-60. · 3.88 Impact Factor