Are resistance (R) proteins (encoded by R genes) involved in pathogen Avr protein recognition/interaction only? Or do genes associated with plant immune signalling or other pathogen defence mechanisms also fall into the category of R gene? For example pathogeneis related (PR) protein encoding genes or genes involved in salicylic acid signalling?
Ruby Metzner Proteins encoded by R-genes (NBS-LRR for instance) do not have proved direct interaction with avr-proteins (T3SS effectors for instance). But, it is known that they interact with products of avr-proteins interaction with target plant molecules. Thus, R-proteins must have reaction with products of some other interactions in plant proteome. "NBS-LRR genes originated in the common ancestor of the whole green lineage, and have rapidly diverged into three subclasses with different domain combinations (TNL, CNL, and RNL) before the split of green algae". Shao, Zhu-Qing, et al. "Revisiting the origin of plant NBS-LRR genes." Trends in plant science 24.1 (2019): 9-12.
"It is likely that R-proteins might contribute toward the symbiosis of fungi and early land plants. Taken together, we propose that the emergence of R-genes provided early land plants with the genetic toolkit needed for survival in a terrestrial environment and might play an important role in plant land colonization."
Out of Water: The Origin and Early Diversification of Plant R-Genes
Yuxia Gao, Wenqiang Wang, Tian Zhang, Zhen Gong, Huayao Zhao, Guan-Zhu Han
Plant Physiology May 2018, 177 (1) 82-89; DOI: 10.1104/pp.18.00185
The PR genes which have been largely associated with mainly biotic stress tolerance are currently being linked to multiple stress tolerance including adaptation to abiotic stresses like desiccation, etc. as well.
The attached review might give some insights:
Article Pathogenesis-Related Proteins and Peptides as Promising Tool...
Some of the effectors secreted by the pathogens (called AVR proteins) can be recognized directly or indirectly by resistance (R) proteins from the plant. This recognition usually triggers defense responses including the hypersensitive response and results in resistance of the plant. While single AVR genes recognized by their corresponding R gene were identified, more and more complex interactions between AVR and R genes are reported (e.g., AVR genes recognized by several R genes, R genes recognizing several AVR genes in distinct organisms, one AVR gene suppressing recognition of another AVR gene by its corresponding R gene, two cooperating R genes both necessary to recognize an AVR gene).
Article Complex Interactions between Fungal Avirulence Genes and The...
The resistance (R) genes of the host employ several mechanisms to confer resistance to host plants:
- The R protein interacts directly with an Avr gene (Avirulence gene),
- The R protein guards another protein that detects degradation by an Avr gene,
- The R protein may detect a Pathogen-Associated Molecular Pattern (PAMP) or alternatively called microbe-associated molecular pattern (MAMP), and
- The R protein encodes enzyme that degrades a toxin produced by the pathogen.
https://en.wikipedia.org/wiki/R_gene
Most identified R genes are polymorphic in plant populations, which led to their initial characterization and use in plant breeding programs. However, individual plants have up to a few hundred R gene analogs that make no identified contribution to resistance. Many of these R gene analogs are also fixed in plant species and are thought to contribute to non-host resistance. After more than 25 years of R gene cloning, R genes have been classified by Nine Mechanisms, details of which may be accessed at:
https://academic.oup.com/plcell/article/30/2/285/6099082
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