Pathogenesis-related (PR) proteins are a group of proteins that are induced in plants in response to pathogen attack, stress conditions, or signaling molecules like salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). These proteins play important roles in plant defense, particularly in systemic acquired resistance (SAR) and induced systemic resistance (ISR).
PR Class | Name / Activity | Function | Examples |
PR-1 | Unknown (marker for SAR) | Antifungal activity, defense signaling | PR-1a in Tobacco |
PR-2 | β-1,3-glucanases | Degrades fungal cell walls | Glucanase in Tomato, Tobacco |
PR-3 | Chitinases (Type I, II, etc.) | Degrades chitin in fungal cell walls | Endochitinase in Rice, Wheat |
PR-4 | Chitin-binding proteins | Antifungal, chitin-binding | Win1 proteins in Barley |
PR-5 | Thaumatin-like proteins | Osmotic stress response, antifungal | TLPs in Tobacco, Grapevine |
PR-6 | Proteinase inhibitors | Inhibits proteases from pests/pathogens | PINs in Tomato, Potato |
PR-7 | Endoproteinases | Degrades proteins, defense signal regulation | Subtilisin-like proteases |
PR-8 | Class III chitinases | Chitin degradation | Found in Maize, Wheat |
PR-9 | Peroxidases | Lignin formation, oxidative burst | APX and POX in Rice, Arabidopsis |
PR-10 | Ribonuclease-like proteins | RNA degradation, antimicrobial | PR-10 in Potato, Pea |
PR-11 | Chitinases (Type I) | Similar to PR-3 and PR-8 | PR-11 in Tobacco |
PR-12 | Defensins | Small peptides, antifungal/antibacterial | Rs-AFP in Radish |
PR-13 | Thionins | Membrane permeabilization | Pp-thionin in Barley |
PR-14 | Lipid transfer proteins (LTPs) | Cutin biosynthesis, antimicrobial | LTP in Arabidopsis, Rice |
PR-15 | Germin-like proteins | Oxalate oxidase activity, H₂O₂ production | Germin in Wheat, Barley |
PR-16 | Oxalate oxidases | Produces H₂O₂; antifungal | Germin-like oxalate oxidases |
PR-17 | Unknown | Induced under biotic stress | Novel proteins with defense roles |
Defense Roles of PR Proteins:
- Direct antimicrobial activity: Lyse or inhibit pathogen growth.
- Signal amplification: Promote expression of other defense genes.
- Cell wall strengthening: Via peroxidases, protein cross-linking.
- Systemic resistance: PR-1 is a hallmark of SAR activation.
