Evolution of views on plant immunity: from Flor’s “gene-for-gene” theory to the “zig-zag model” developed by Jones and Dangl
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.