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- 1. Receptor sites for elicitors
- 2. Elicitors • Elicitors are signal molecules that elicit defense mechanisms in plants (Scheel and Parker,1990) • When fungal cell wall comes in contact with plant cell, elicitors are released and bind with receptor molecules results in induction of defense mechanism
- 3. Chemical nature of elicitors • Elicitors – Glycoproteins • Cladosporium fulvum • Colletotrichum lagenarium – Carbohydrates • Colletotrichum graminicola • Phytophthora megasperma f.sp. glycinea – Fatty acids • Phytophthora infestans – Peptides • Phytophthora spp. (Elicitins, cryprogenin)
- 4. Avr gene Avr gene R GENE R GENE DEFENSE DEFENSE
- 5. Host Plant Receptors • The location of host receptors that recognize pathogen elicitors is not generally known • but several of those studied appear to exist outside or on the cell membrane,whereas others apparently occur intracellularly. • Eg. powdery mildew of cereals, a soluble carbohydrate that acts as an elicitor from the wheat powdery mildew fungus Blumeria graminis f. sp. tritici • The elicitor alone, in absence of the powdery mildew fungus, did not induce a hypersensitive response
- 6. Receptor • Types of receptors • Oligosaccharide elicitor-binding protein • Hepta beta –glucoside –binding proteins • Glycoprotein elicitor-binding proteins • Polypeptide elicitor –binding proteins • Yeast glycopeptide elicitor-binding proteins
- 7. A Model for Defense Gene Induction (From work in T. Boller’s lab) Late Defense Genes TF Inactive TF Active TF Signal Transduction Early Defense Genes Flag22 FLS2 (LRR) (Kinase) (MAPK6)
- 8. • elicitor with its putative receptor as a two-step process. Binding of the N terminus is presented as the first step, and activation by the C terminus is the second step Model for the Interaction of Flagellin with Its Receptor.
- 9. R gene Crop Binding site Function RPW8 Pto Cf-2–Cf-9 Xa21 RPM1, RPS2 Arabidopsis Tomato Tomato Rice Arabidopsis Cell membrane Cell membrane Plant Cell wall Plant Cell wall Cell Cytoplasm Membrane–associated, transcription regulating, mediating broad- spectrum resistance Cytoplasmic signal-transducing serine–threonine protein kinase Extracellular LRRs with transmembrane anchor Extracellular LRRs, with a transmembrane receptor and a cytoplasmic serine–threonine kinase cytoplasmic, membrane associated. Contain LRRs, NBS, and a coiled coil domain
- 11. Oligopeptide elicitor and Oligosaccharide elicitor-binding protein Phytophthora megasperma f.sp. glycinea (Pep-13) its binding site in microsomal and plasma membrane 91-kDa protein identified in parsley membranes is the oligopeptide elicitor receptor mediating activation of a multicomponent defense response. The first report on the identification of an elicitor binding site implicated a 70-kDa protein from soybean microsomal membranes to be a constituent of a heptaglucan elicitor receptor,
- 12. Microbial elicitors and their receptors in plants Hepta beta –glucoside –binding proteins • mycelial walls of Phytophthora megasperma f. sp. glycinea • Binding site-soybean microsomal membranes. Oligochitin elicitors-binding proteins • Rhizobium leguminosarum • Binding site-membranes of tomato and rice Glycoprotein elicitor-binding proteins • Puccinia graminis f.sp.tritici • Glycoprotein elicitor-binding site in wheat have not yet been reported
- 13. Yeast glycopeptide elicitor-binding proteins • Yeast glycoproteins • Binding site –plasma membrane Polypeptide elicitor –binding proteins • Mycelial wall of phytopthora sojea • Binding site-parsley microsomal membrane Cryptogen elicitin binding protein • Phytopthora spp. • Binding site –tobacco plasma membrane
- 14. • RECEPTOR – MODELS • Classical receptor–ligand model • Co-receptor model • Guard model • Protease-dependent defence model Bonas& Lahaye2002