Plant immunity to pathogens Flashcards
Nematodes
Large multicellualr animals (like worms)
Oomycete
Fungus-like eukaryotic microorganisms
Phytopathology
Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). (Not including insects, mites or other stuff that eat the plant tissue.)
Disease triangle
Host (susceptible to pathogen), pathogen (overcome plant defenses), environment (must be in favor of pathogen)
Disease pyramid
The disease triangle + the human factor (growing practice, migration of plants and people, introducing pathogens, etc.)
What defenses does the plant have against pathogens?
Physical barriers - cuticle, cell wall
How can pathogens enter the cell despite the physical barriers?
Through wounds or stomata
אפרסוריום
תא מסויום בפטריות פתוגניות שמשמת לפריצת דופן התא של הצמח
Necrotroph
Necrotrophs kill cells and then consume the contents
Biotroph
Biotrophs live within host tissue without causing death
Hemibiotrophs
Hemibiotrophs can switch from biotroph to necrotroph
What are the defense responses of a plant?
- Increase synthesis of stress hormone
- Up regulate pathogenesis-related (PR) genes
- Synthesis of antibicrobial compounds
- Producing reactive oxygen species (ROS)
- Production of polysaccaride callose
Phytoanticipins
Secondary metabolites that provide a constant defense
Phytoalexins
Secondary metabolites synthesized in response to a pathogen
PTI
Pattern Triggered Immunity:
In response to a signal from a receptor on the membrane:
* kinase cascade leading to transcriptional responses
* calcium ion influx
* reactive oxygen production
PRR
Pattern recognition receptors
חלבונים שיודעים לזהות פתוגנים
LRR
Leucine rich repeat - part of the pattern recognition receptors
Effectors
Proteins secreted by the bacteria that repress the PTI (Pattern Triggered Immunity) mechanisims
R proteins
R proteins are LRR (leucine rich repeat) that recognize effectors and have a stronger defensive response
ETI vs PTI
Effector-Triggered Immunity is faster, stronger and more prolonged than PTI
ETI
Effector-Triggered Immunity
The zig-zag model
Pathogen is recognized –> Pattern triggered immunity (PTI) –> Pathogen effectors suppress defense response (Effector triggered susceptibility) –>
Effector is recognized and you have the effector triggered immunity (ETI)
Systemic Acquired Resistance (SAR)
Systemic acquired resistance (SAR) is a “whole-plant” resistance response that occurs following an earlier localized exposure to a pathogen.
I.e., uninfected tissues show enhanced resistance to pathogens that attacked a different part of the plant
תפקידים של חומצה סליצילית
Salicylic Acid
- Systemic acquired resistance
- Induces defense responses
- Reponses to biotrophic pathogens
What causes sythesis of salicylic acid?
The pathogen.
MeSA
A derivative of SA (salicylic acid) that plays a role in long distance singling (between plants)
מתנדף בקלות
Hypersensitive response (HR)
The hypersensitive response (HR) is a mechanism, used by plants, to prevent the spread of infection by microbial pathogens. The HR is characterized by the rapid death of cells in the local region surrounding an infection
מי מפעיל את ה
hypersensitive response?
R proteins and salicyclic acid
Herbivory
Herbivory is the consumption of plant material by animals, and herbivores are animals adapted to eat plant
Jasmonate JA acid
Response to necrotrophic pathogens and anti-herbivory responses
Can move between plants because it’s very
נדיף
מה מנגנון הפעולה של
JA?
משנה ביטוי גנים על ידי שיחרור רפרסוריים
How do plants overcome being eaten by insects?
They produce proteinase (enzyme that breaks down protein) inhibitors that interfere with the insect digestion and kill it
What are the two mechanisms for passing signals between plants?
- Volatile organic compound
חומרים נדיפים - Common mycorrhizal networks
קו אבולוציה בין צמחים לבין חרקים טורפים
זחל אוכל צמח שיש בו חומרים שעוברים פירוק ומתנדפים. החומרים האלו מהווים סיגנל לחרקים טורפים לזחל ואלו מחסלים את הזחלים
Biotrophic
Biotrophs live within host tissue without causing death
Hemibiotrophs
Hemibiotrophs can switch from biotroph to necrotroph
Necrotrophs
Necrotrophs kill cells and then consume the contents
What chemical “deals” with biotrophic organisms
Salicylic acid
What chemical “deals” with necrotrophic organisms?
Jasmonates
Why are Salicylic acid and Jasmonates mutually antagonistic?
Because SA “deals” with biotrophic organisms (who want to keep the plant alive) and Jasmonates “deals” with necrotrophs who want to kill the plant
What role does ethylene play in defense?
The gene FLS2 which is responsible for pathogen recognition is regulated by ethylene
What happens if a plant is impaired in ethylene responses?
The plant won’t recognize pathogen and will therefore be more susceptible
What effect does ethylene have on plant leaves?
Senescence
אתלין מגביר הזדקנות של עלים ועלי כותרת
What effect does ethylene have on fruit and flowers?
Ethylene shortens the “life” of flowers and fruit.
Promotes fruit softening and flavor and color development
What can be used to extend fruit shelf life?
Limit ethylene effects by limiting production, removal from air or interfere with binding to a receptor
What’s unique about ethylene as a hormone?
- Gas
- Hydrophobic
- Very small
What processes does ethylene play a part in?
- fruit ripening
- leaf and petal senescence
- cell division and elongation (promotes)
- root growth
- stress responses
- wound responses
- sex determination
What happens if there is flooding?
Roots can’t take up oxygen and become hypoxic which causes ethylene production –>
התארכות הפרקים
ACC synthase
האנזים הראשון ביצירת אתלין, קובע את רמת האתילן שתיווצר
What effects does ethylene have in etiolated seedlings?
- Reduced elongation
- Hypocotyl swelling
- Apical hook exaggeration
What type of regulation do ethylene regulated genes have?
Negative -
Ethylene binds to a receptor releases a protein and that permits transcription
איזה רצפטור יש לאתילן?
אטום מתכת
Climacteric fruit
The climacteric is a stage of fruit ripening associated with increased ethylene production and a rise in cellular respiration.
Which hormone initiates the ripening process
ethylene
How do defense responses effect growth rate?
They reduce the growth rate
