Abstract
The study of plant defence mechanisms in response to pathogens in the mid-20th century resulted in Harold Flor’s gene-for-gene interaction hypothesis, which became recognised as central to the study of phytoimmunity. According to this theory, the outcome of interactions in plant – pathogen phytopathosystems – i.e. compatibility or incompatibility – is controlled genetically in interacting organisms and determined by the presence of specific genes in both pathogen and plant: resistance genes in the plant and avirulence genes in pathogen. The latest achievements in phytoimmunology, obtained with the help of modern molecular biology and bioinformatics methods, have made a significant contribution to the classical understanding of plant immunity and provided grounds for a modern concept of phytoimmunity consisting in the “zig-zag model” developed by Jonathan Jones and Jefferey Dangl. Plant immunity is currently understood as being determined by an innate multi-layer immune system involving various structures and mechanisms of specific and non-specific immunity. Recognition by plant membrane receptors of conservative molecular patterns associated with microorganisms, as well as molecules produced during cell wall disruption by pathogen hydrolytic enzymes forms a basic non-specific immune response in the plant. Detection of pathogen effector molecules by plant intra-cellular receptors triggers a specific effector-triggered immunity, resulting in the development of the hypersensitive response, systemic resistance and immune memory of the plant. Virulence factors and pathogen attack strategies on the one hand, and mechanisms of plant immune protection on the other, are the result of one form of constant co-evolution, often termed an “evolutionary arms race”. This paper discusses the main principles of Flor's classical “gene-for-gene interaction” theory as well as the molecular-genetic processes of plant innate immunity, their mechanisms and participants in light of contemporary achievements in phytoimmunology.
Highlights
In natural habitats, plants have to co-exist with a large variety of microorganisms, many of which are pathogenic
Innate recognition is based on detection by membrane receptors of “alien” molecular structures, which are inherent to microorganisms, but are absent from the host plant
The molecules recognised by Pattern Recognition Receptors (PRRs) are invariant and conservative for each class of microorganisms and are denoted in respect to their origin either as Pathogen-Associated Molecular Patterns (PAMP) or Damage-Associated Molecular Patterns (DAMP)
Summary
Plants have to co-exist with a large variety of microorganisms, many of which are pathogenic. The molecules recognised by PRR are invariant and conservative for each class of microorganisms and are denoted in respect to their origin either as Pathogen-Associated Molecular Patterns (PAMP) or Damage-Associated Molecular Patterns (DAMP) Their detection results in the activation of a series of basic, non-specific plant defence responses (Pattern-Triggered Immunity – РTI): generation of reactive oxygen species (ROS) and nitric oxide (NO), synthesis of phytoalexins, lignification of cell walls and callose deposition, as well as a number of other mechanisms [4]. CLASSICAL THEORY OF PHYTOIMMUNITY The study of plant defence mechanisms in response to pathogens in the middle of the 20th century resulted in the formation of phytoimmunity theory, which has been recognised as central to the study of plant immunity According to this theory, the outcome of interactions in phytopathosystems is under genetic control [7]. Should any component of the Avr/R pair be absent or altered, they become compatible and the disease develops [11]
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