Plant Microbe Interactions Flashcards
What are the rhizosphere and phyllosphere?
Rhizosphere: The root-associated soil environment.
Phyllosphere: The above-ground environment on plant surfaces, such as leaves.
What are the three types of plant-microbe interactions?
- Commensalism: Microbes benefit, plants unaffected.
- Mutualism: Both benefit (e.g., Rhizobia).
- Parasitism: Microbes harm the plant (pathogens).
How do biotrophic and necrotrophic pathogens differ?
Biotrophic: Invade living cells (e.g., powdery mildew).
Necrotrophic: Invade dead cells (e.g., Botrytis).
What determines plant resistance to pathogens?
Resistance depends on R-genes that recognize pathogen effectors, triggering plant defense responses.
What is the hypersensitive response (HR), and how does it protect plants?
HR triggers localized cell death to limit pathogen spread, often accompanied by production of reactive oxygen species (ROS).
How do effectors and R-genes interact in race-specific resistance?
Pathogen effectors are recognized by plant R-genes, leading to resistance. If no R-gene exists, the pathogen can colonize the plant.
What is systemic acquired resistance (SAR)?
SAR is a broad-spectrum immune response triggered after local infection. It spreads resistance signals throughout the plant.
What role does salicylic acid play in SAR?
Salicylic acid triggers local responses but relies on NHP (N-hydroxy-pipecolic acid) for systemic signal transmission to uninfected tissues.
What are PR proteins, and how are they involved in plant defense?
Pathogenesis-Related (PR) proteins are induced during SAR, overexpressed even in systemic tissues across the plant.
13 known PR protiens, discovered due to comparisons in protiens betweeen non SAR and SAR leaves.
Only known PRs:
PR-2: Glucanase (breaks down fungal glucans).
PR-3: Chitinase (targets fungal chitin).
What role do Rhizobia play in nitrogen fixation?
Rhizobia infect root hairs of legumes, form nodules, and fix atmospheric N2 into NH3 using nitrogenase.
What are Nod factors, and how do they initiate nodulation?
Nod factors are lipochitooligosaccharides secreted by Rhizobia. They trigger root hair curling and the formation of infection threads.
How do flavonoids contribute to Rhizobia attraction?
Plant roots secrete flavonoids, which act as chemoattractants to Rhizobia and activate bacterial nod genes.
How do Rhizobia enter plant roots?
Rhizobia enter via root hair curling. They form infection threads that grow into the cortex, where nodules develop.
What happens to Rhizobia inside root nodules?
Rhizobia differentiate into bacteroids that fix nitrogen. They are enclosed in symbiosomes surrounded by a plant membrane.
Why is leghaemoglobin important in nitrogen fixation?
Leghaemoglobin delivers oxygen to bacteroids at low concentrations, protecting nitrogenase (oxygen-sensitive enzyme) while supporting respiration.
What are some plant immunity responses upon pathogen recognition
Pathogen recognition triggers calcium spiking, ROS production, and activation of defense genes
What experiment demonstrated SAR?
Frank Ross (1961): Tobacco plants pre-infected with an avirulent TMV strain showed resistance to a subsequent virulent TNV infection.
How do pathogens suppress plant immunity?
Pathogens secrete effectors that interfere with R-gene signaling or defense responses, allowing colonization.
What is mycorrhizal symbiosis, and how does it benefit plants?
Symbiotic fungi form associations with plant roots, enhancing nutrient uptake (e.g., phosphorus) and improving stress resistance.
How was the role of Nod factors in root hair curling demonstrated?
Mutants lacking Nod factor receptors showed no root hair curling, proving Nod factors are essential for Rhizobia entry.
What are root nodules, and why are they important?
Root nodules are specialized structures on legume roots where nitrogen-fixing bacteria (Rhizobia) convert atmospheric nitrogen (N2) into ammonia (NH3), providing essential nitrogen for plant growth.
What are the key steps in root nodule formation?
- Flavonoid Secretion: Plant roots release flavonoids to attract Rhizobia.
- Nod Factor Secretion: Rhizobia produce Nod factors in response.
- Root Hair Curling: Nod factors induce curling of root hairs, trapping bacteria.
- Infection Thread Formation: Bacteria invade via infection threads.
- Nodule Development: Bacteria differentiate into bacteroids within nodules.
What role do flavonoids play in nodulation?
Flavonoids are chemical signals released by plant roots to attract specific Rhizobia and activate bacterial nod genes, initiating nodulation.
What are Nod factors, and how do they function?
Nod factors are lipochitooligosaccharides produced by Rhizobia. They bind to plant receptors (e.g., NFR1/NFR5 in legumes) and trigger root hair curling and infection thread formation.
