Pathology - Midterm Flashcards
Types of disease resistance
Pathogen specificity
Quantative & Qualitative inheritance
Passive vs active resistance
Types of pathogens
Fungi & Oomycetes Bacteria Viruses Nematodes Parasitic Plants
Biotrophic method of pathogenicity (def)
Lives off healthy cells
- Must avoid detection by the host during early stages of compatible interactions
- Must inhibit defense responses once established.
Hemibiotrophis method of pathogenicity (def)
Infect healthy cells early in the interaction, but grow and reproduce on dead tissue
Necrotrophic method of pathogenicity (def)
Kill cells and live off dead tissue. Produce toxins that may be host specific (even cultivar specific) or nonspecific
Specialists (types of pathogens def)
Narrow host range (single family or species)
Resistance qualitative and race-specific
Generalists (types of pathogens def)
Broad host range encompassing diverse families and genera
Resistance quantitative with no race-specificity
Non-host Resistance (types of pathogen resistance based on specificity def)
The entire plant species is resistant to a specific pathogen or parasite
-very common
Host (cultivar) resistance (types of pathogen resistance based on specificity def)
Some genotypes of the species are resistant, some are not
-often controlled by R genes
Qualitative, or simply inherited (Types of resistance based on inheritance)
Genes often race specific and often follow gene-for-gene model
Often called R genes
Often conditioned by a hypersensitive response
Quantitatively Inherited Resistance (Types of resistance based on inheritance)
Controlled by multiple genes with smaller effects
assumed to be race-nonspecific
Compatible (interaction terminology)
Interaction where the pathogen is virulent an the host is susceptible
Incompatible (interaction terminology)
Interaction where the pathogen is avirulent and the host is resistant.
PAMP-triggered immunity
Pathogen (Microbe) Associated Moldular Patterns
- conserved molecular structures unique to microbes
- (Basal Resistance)
PRRs (Pattern Recognition Receptors) and PAMP
plant transmembrane receptors that recognize PAMPs and activate basal defense
Effector Triggered Immunity (R gene mediated Resistance)
Effector molecules (avirulence Avr proteins) - pathogens have evolved effector molecules to evade/suppress PAMP triggered immunity R Proteins - Plants have evolved recognition receptors (r-proteins) encoded by R (resistance) genes, that detect specific effector molecules
Gene for Gene model hypothesis
Resistance is dominant, virulence is recessive
-only R genes specifically matched with Avr genes result in resistance (incompatability)
Arv gene is recognized by a plant R gene
Direct Interaction - Gene for Gene Model
Receptor-Ligand model
direct binding of R gene and Avr gene products
Indirect Interaction - Gene for Gene Models
Guard Model: Modification of host target by effector results in activation of R protein
Decoy Model: Effector target is a decoy evolved through gene duplication or target mimicry that only functions in the perception of pathogen effectors
R-Gene Mediated Resistance (signaling pathways)
Effective against biotrophs
-Gene for gene recognition
Salicylic Acid (SA) Dependent Signaling and Systemic Aquired Resistance (SAR) (signaling pathways)
- Implicated in PAMP and SAR
- Feed back loops that increase cell death
Defense Responses activated by Jasmonic Acid (JA) and Ethylene (ET) signaling (signaling pathways)
Effective against necrotrophic pathogens & insects
similiar to wounding responses
In Gene-For-Gene Interactions which traits are dominate?
Resistance and Avirulence
ETI -def
NBS-LRR R genes directly recognize Avr products, and initiate a defense response characterized by HR
PTI -def
LRR-RLKs, recognition may or may not be associated with HR
most similar to PAMP
Significance of tandem arrays in R-genes
Tandem arrays, etc
Retain orginial function but increases the diversity in genetics
Indirect Recognition (R-Avr systems) aka guard model, decoy model
Imposes selection against Avr effector function
R-gene is guarding a change in the target
Direct Recognition
Imposes selection on Avr effector structure
Direct Recognition leads to ___ at R and Avr Loci
diversifying selection and high levels of allelic polymorphism
Indirect Recognition leads to ___ R and Avr genes
balancing selection for functional or nonfunctional
Segregation of two independent genes
Number of geneotypes =
3^n (n=number of segregating genes)
Segregation of two independent genes
F2 genotypic rations
15:1 is typical when it only takes one gene to confer resistance
Segregation of two independent genes
Number of phenotypes =
2^n (n=number of segregating genes)
