Lecture 8 Flashcards
what % of crops is lost to insects and diseases every year
40%
disease triangle
level of disease or resistance observed depends on: pathogen genotype–environment–plant genotype
pathogen (disease triangle)
has virulence factors to infect a particular species
plant (disease triangle)
must be susceptible when the pathogen tries to infect
environmental conditions
must favour disease development
specialist pest
microbe or insect that feeds on one or a few plant species/organs
generalist pest
microbe or insect that feeds on many plant species/organs
entry of pathogen into plants
direct penetration
penetration through natural openings
penetration through wounds
entry of viruses into plants
via insects, insects interact with plant by eating it or other interactions and provide a vector of penetration
what must a successful plant pathogen have:
ability to obtain nutrients, grow, and reproduce in the plant environment
Disease cycle
Inoculation
Penetration
Infection (creating a favourable environment, obtaining nutrients and reproducing)
Erwinia soft rot
common among vegetables because environmental conditions require cold and humid conditions common in a refrigerator
Necrotrophs
kill plant cells and live on dead plant tissue
biotrophs
invade and grow in living plant tissues manipulate plant metabolism
hemibiotrophs
begin infection as biotrophs then switch to necrotorophy later in infection to spread to next plant
constitutive plant defence
performed defences
constitutive pathogen defence
cell walls
cuticles
constitutive herbivore defence
glucosinolates in mustard nicotine in tobacco cannabinoids in cannabis caffeine in coffee vanilla in vanilla orchid opium in opium poppy taxol in pacific yew
Induced pathogen defence
prevent pathogen entry via closing of stomata
production of ROS as an antimicrobial
pathogenesis related proteins
phytoalexin production
cell wall strengthening at infection site
Phytoalexins
antibiotic-like antimicrobial compounds
pathogen-related PR proteins
antimicrobial agent ex: chitin’s degrades chitin in fungal cell walls, glucanase degrades fungal cell walls, lysozyme punch holes in bacterial cell walls
induced cell wall strengthening
at infection site, addition of calls, lignin, hydroxy-rich glycoproteins all strengthen the wall to stop entry of pathogens or stop the secretion of effectors into the plant
Induced Responses vs herbivours
anti herbivore compounds and proteins in organs
local defence
recognition of danger signals
R gene-mediated resistance
local defence against biographic pathogens using effector triggered immunity
Basal Resistance
local defence vs biographic pathogens using PAMP triggered immunity
age related resistance
a form of local defence against biographic pathogens
PAMP-triggered immunity
local defence vs neurotrophic pathogens and insects
systemic immunity
via inter organ communication
systemic acquired resistance vs biographic pathogens
systemic wound response vs neurotrophic pathogens and insects
Explain what is meant by the “Arms Race”
most plants are resistant to most pathogens unless the pathogen has evolved a way to get around the plant defence. plants and pathogens are in an evolutionary arms race
PAMP
pathogen associated molecular patterns
MAMP
microbe associated molecular patterns
Basal Resistance
PAMP triggered immunity
Plant Pattern Recognition Receptors (PRR) recognize PAMPs like flagellin triggering a signalling pathway
PAMP signalling pathway
ROS and Ca2+ signalling, Kinases and transcription factors, stomatal closure, cell wall strengthening, production of antimicrobials
R Gene Mediated Resistance
effector triggered immunity (ETI)
plant resistance genes encode membrane bound or cytoplasmic R Receptor proteins which recognize pathogen virulence/effector proteins causing a hypersensitive response
Overview of R gene-mediated Resistance/ETI
plant has functional basal resistance that pathogen effector suppresses
r-receptor recognizes pathogen virulence protein/effector
HR Hypersensitive Response occurs
HR
Hypersensitive response: rapid necrosis at infection site, form of programmed cell death, pathogen numbers reduced due to loss of life host cells and very dry conditions in HR lesion
not effective vs necrotrophs
ETI/R-gene signalling pathway
ROS and Ca act as signalling molecules
antimicrobial agents accumulate
cell wall strengthened
HR cell death
Resistance
receptors perceive pathogens, signalling initiates fast and successful deployment of defence
Susceptibility
pathogen employs virulence effectors &/ toxins to suppress plant defence leading to pathogen success and disease
Pst
Pseudomonas syringas pv tomato
needs water on the leaves, needs stomata to open so bacteria can enter. inoculation forces bacteria to enter
Bacterial pathogens secrete toxins and effector proteins into the plant during infection to:
suppress plant resistance response
manipulate plant to promote growth and development of pathogen
Successful basal resistance to bacteria
begins with perception of bacteria with PAMP receptors–initiates signal cascade–closure of stomata
Pseudomonas
inhibit plant response using coronation causing stomata to reopen
Coronatine
toxin which is used by pseudomonas to re-open plant stomata; pseudomonas Cor- mutants are unable to reopen the stomata even if they successfully inoculate the plant;
T3SS
Type 3 Secretion System: used by pathogens to secrete effectors into plant cells creating a favourable environment
pathogen effectors:
pathogens secrete effectors to create a favourable environment
SWEET
gene encoding sugar transporters on plasma membranes
RIN4
positive regulator of Basal R/PAMP triggered immunity
AvrRpm1 & AvrRps2
pathogen effectors that disrupt RIN4 function
AvrRpm1
phosphorylates RIN4
AvrRpt2
degrades RIN4
RPM1
R-receptor that recognizes phosphorylated RIN4 and activates R gene-mediated Resistance or ETI
RPS2
R-receptor that recognizes RIN4 degradation and activates R gene-mediated Resistance or ETI
RPM1 and RPS2 analogy
backup generator, recognizes that defence has been deactivated and it reactivated. its a backup security mechanism
Indirect interaction of R and AVR/Effector
RPM1 and RPS2 indirectly recognize avrRPM1 and avrRPT2 by recognizing the phosphorylation or degradation of RIN4 respectively and activating plant defence
fungus plant interaction
Blumeria fungal pathogen of barley, arabidopsis is resistant because of PTI which stops penetration builds new cell wall material and ROS which inhibit hyphen entry and fungal growth. Visualized using ROS stain showing attempted penetration sites
DAMP
damage associated molecular patterns
Plant Defence Syndrome:
plants perceive a pathogen and do all actions (cell wall strengthening, closing stomata, antimicrobial ROS, signalling ROS, pathogenesis related proteins) which might help them if another pathogen comes along
why might inoculation of a plant with one pathogen help it defend against another pathogen?
the plant will experience the plant defence syndrome which will initiate all defence mechanisms making it prepared for the second pathogen and allowing it to defend itself more effectively and quicker
systemic resistance
similar to immunization; initial infection or attack leads to production of long distance signals which move to distant leaves priming them to respond in resistance manner for when the pathogen or insect moves to a new leaf
SAR
Systemic Acquired Resistance; infect/immunize plant with bacteria to protect against viruses, fungi and other bacteria
Systemic Wound Response
insect chews on a lower leaf, phloem mobile signal causes upper leaves to express defence related genes increasing ethylene and producing anti-feeding proteins
plant to plant communication
plants alert surrounding plants about pathogen attack by producing volatile methyl salicylic acid during SAR
plant calls for help from community
insect and plant produce volatile compounds during insect feeding attracting predators of attacking insect; tobacco horn worm is attacked by wasp which lays its pupae on the worm which will feed on the worm saving the plant
Rhizobia bacteria and legumes
bacteria fix nitrogen into NH3
plant provides nodule environment and carbon source
Mycorrhizal fungi
colonize 80% of plants studied; fungal hyphae grow in soil providing plant nutrients, plant provides carbon source, fungal hyphae expand ability of plant to explore soil for nutrients good for farmers because they need less fertilizer
Ectomycorrhizae
fungus surrounds root as a sheath; interacts with woody plant roots and forms toadstools that produce fungal spores; interacts with 10% of plants
Endomycorrhizae
fungus grows inside roots and forms transfer structure called abuscule; grow around cortical cells without penetrating them; plant provides carbon, fungus provides phosphate to plant cortical cell
does arabidopsis interact with rhizobia or mycorrhizae?
no