Plant Pathogen Resistance Overview

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Questions and Answers

What role does Pto play in relation to the effector AvrPto?

It competes with FLS2 for AvrPto binding. (correct)

It blocks the immune response of the plant.

It triggers disease symptoms in the plant.

It enhances FLS2's binding affinity.

Which model highlights the interaction involving guarded effector targets?

Guard model (correct)

Decoy model

Quantitative model

Resistance model

What is considered a promising area in plant disease resistance breeding?

Helical resistance genes.

Qualitative resistance genes.

Transformational gene editing.

Quantitative disease resistance mechanisms. (correct)

Which effector is known to bind FLS2 and block plant immune responses?

AvrPto Signup and view all the answers

What might be necessary for long-lasting effectiveness in plant resistance breeding?

Deployment of multiple R genes. Signup and view all the answers

Which of the following is NOT a characteristic of quantitative resistance?

Immediate and complete immunity. Signup and view all the answers

What is essential for advancing the understanding of plant-microbe interactions?

Isolation of resistance genes. Signup and view all the answers

What effect does the utilization of quantitative resistance genes (QRLs) imply for crop improvement?

They offer potential for valuable applications. Signup and view all the answers

What is the primary characteristic of NBS-LRR genes in plants?

They contain a nucleotide-binding site and a leucine-rich repeat domain. Signup and view all the answers

What is suggested about the recessive resistance gene xa13 in rice?

It acts as a susceptibility allele rather than a traditional resistance gene. Signup and view all the answers

Which of the following statements about recessive resistance is true?

It is considered a passive process due to a lack of susceptibility. Signup and view all the answers

What role does the pvr2 locus play in pepper plants?

It encodes an initiation factor that provides recessive resistance to PVY. Signup and view all the answers

Which breeding method can be used to develop disease-resistant plants?

Marker-aided selection and traditional breeding. Signup and view all the answers

Which group of NBS-LRR genes is characterized by coiled-coil domains?

The CC group genes. Signup and view all the answers

Why is susceptible resistance considered an important area of study?

It may indicate new pathways for employing disease resistance. Signup and view all the answers

What is the hypothesis regarding the functioning of recessive resistance genes?

They operate passively due to absent susceptibilities. Signup and view all the answers

What contributes to the resistance of Arabidopsis to Phytophthora brassicae?

The sequential action of indole glucosinolates and camalexin Signup and view all the answers

In the context of innate immunity, what action does the bacterial virulence protein xa21 perform?

It suppresses host innate immunity Signup and view all the answers

Which gene is known to block innate immunity in plants by targeting receptor kinases?

AvrPto Signup and view all the answers

What is the role of quantitative resistance loci in plant breeding?

They enhance resistance through multiple genes. Signup and view all the answers

How do salicylic acid induction-deficient mutants in Arabidopsis respond after pathogen inoculation?

They express PR-2 and PR-5. Signup and view all the answers

What is a barrier that pathogens must overcome to successfully infect plants?

Pattern recognition receptors Signup and view all the answers

Which mechanism is employed by strains of Pseudomonas syringae to evade plant defenses?

Deploying effector proteins like AvrPto Signup and view all the answers

Which plant defense response is primarily associated with pathogen-associated molecular patterns (PAMPs)?

PAMP-triggered immunity Signup and view all the answers

Study Notes

Plant Resistance to Pathogens

Plants constantly battle against microbial and other pathogens.
Pathogens invade plants via leaf and root surfaces or natural openings like stomata.
Pathogens degrade cell walls, introduce effectors, and disrupt host activities
Plants have evolved physical and chemical barriers and a two-tiered immune system (PTI and ETI).

Qualitative Disease Resistance

Qualitative resistance (controlled by a major gene) is effective against specific pathogens.
Primarily involved in defense against biotrophic pathogens.
R genes are typically NBS-LRR genes (Nucleotide-binding site and Leucine-rich repeat).
These genes encode proteins with various domains (TIR, CC, LRR, etc.).
Major genes can be overcome by new virulent pathogens
Quantitative disease resistance is more durable.

Quantitative Disease Resistance

Quantitative resistance (controlled by multiple genes with minor effects) is more durable against a wide range of pathogens.
Involves multiple genes with minor effects.
Fewer selection pressures against pathogen variants.
Includes genes related to morphology, defense signaling, and secondary metabolites.
Some QRLs are related to flowering time and basal defense.

Mechanisms Underlying Plant Resistance

Biotrophic Pathogens: Plant defenses are largely due to gene-to-gene resistance leading to hypersensitive response (HR).
Necrotrophic Pathogens: No clear gene-for-gene relationship, relying on basal defenses.
- Include pathways like salicylic acid (SA), jasmonic acid (JA), and ethylene signaling.
- Phytoalexins (e.g., camalexin) play vital roles.

RNA Silencing in Plant Resistance

RNA silencing is a primary defense mechanism against viral pathogens.
Triggers are double-stranded RNA.
Process involves a Dicer/Dicer-like protein and RISC complex to degrade or silence homologous RNA and genes.
Viruses might produce proteins that suppress host RNA silencing to facilitate infection.

Two-Tiered Innate Immune System in Plants

Plants lack mobile defenders and a somatic adaptive immune system.
Their immune system has two main tiers:
- PTI (PAMP-triggered immunity): activated by pathogen-associated molecular patterns (PAMPs).
- ETI (Effector-triggered immunity): activated by recognizing pathogen effectors.

Elicitor-Suppressor and Elicitor-Receptor Models

Elicitor-suppressor model: Pathogens use general elicitors that trigger defense responses countered by specific suppressors.
Elicitor-receptor model: Pathogens proteins or metabolites are recognized and trigger defense by resistance genes.

Guard and Decoy Models

Guard model: R proteins guard specific host proteins targeted by effectors.
Decoy model: Host proteins act as decoys to distract effectors and thus help detect and defend against pathogens.

Quantitative Resistance Loci (QRLs) and Major Genes

QRLs are useful for broad-spectrum resistance.
Major genes contribute to resistance, but their effectiveness is often short-term.

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Description

Explore the fascinating world of plant resistance to pathogens through qualitative and quantitative approaches. Discover the mechanisms plants use to defend themselves, including their two-tiered immune system and the roles of various resistance genes. Understand how both major and minor genes contribute to plant defense and the implications for agricultural practices.