Abstract
Interactions between disease resistance (R) genes in plants and their corresponding pathogen avirulence (Avr) genes are the key determinants of whether a plant is susceptible or resistance to a pathogen attack. Evidence has emerged that these gene-for-gene interactions in the perception of pathogenic invasions and development of acquired resistance in plants involve different molecular and hormonal transduction pathways, which are still poorly understood. It has become apparent that plants actively produce several phytohormones such as ethylene, jasmonate, salicylic acid, and reactive oxygen intermediates prior to upregulation of R genes. The physiological role of these molecules in plant resistance to pathogens is beginning to attract attention. The use of transgenic plants in recent attempts, including development of mutants with altered R genes, has provided new insights into the mechanisms involved in pathogen perception, signal transduction and subsequent resistance to disease in plants. This review tries to summarize current knowledge of pathogen-related genes in plants, and how they can be use to improve disease resistance in agronomically valuable plants. It also describes the molecular basis of defense mechanisms in plants under pathogen attack. Key words: Avr, resistance gene, hypersensitivity, pathogenesis-related proteins, transgenic, plant-defense.
Highlights
Being sessile organisms, plants are often exploited as a source of food and shelter by a wide range of parasites including viruses, bacteria, fungi, nematodes, insects and even other plants
The defense response in plants appears to be activated by ligand/receptor interactions, in which Avr gene and pathogen or plant surface-derived elicitors serve as ligands for receptors located in the plasma membrane or in the cytosol
One can expect many more R genes to be cloned if discoveries in this area are accessible worldwide
Summary
Plants are often exploited as a source of food and shelter by a wide range of parasites including viruses, bacteria, fungi, nematodes, insects and even other plants They have developed remarkable strategies to adapt to environmental changes by using a range of constitutive or inducible biochemical and molecular mechanisms. Specificity of the interactions between plants and pathogens is still an incomprehensible phenomenon with a complicated hierarchy of biological organization Elucidation of this phenomenon represents an important task of contemporary plant pathology (Scheel, 1998; Nimchuk et al, 2001). We point out the gaps in the knowledge of basic defense systems of plants against pathogen attacks It is not the purpose of this review to cover the whole subject of molecular interactions between plants and pathogens. An appendix containing a glossary of pathology-related terms used in this text is provided at the end of the report
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