Pathogens Flashcards
Necrotrophs
Kill host and feed on dead remains
Biotrophs
Manipulate host development to keep it alove and feed on cells
Plant produces compounds to help pathogen growth
Detrimental to yields and resources diverted from seeds
Galls
Home for pathogen
Sink for nutrients so resources diverted
Development controlled by growth regulators
Agrobacterium tumefaciens
Manipulate host to make undifferentiated gall through auxin and cytokinin manipulation
Pathogen can transfer genes (in T-DNA) from TI plasmid for AU and CK biosynthesis to host to make plant produce it
Plant makes AU, CK and opine sugars - only bacteria can feed on this to grow and draw more photosynthate into gall
High AU supresses defences
Levels of AU and CK
Ratio controls plant growth
Low both = low growth
High AU, low CK = more roots
Low AU, high CK = more shoots
High both = promotes cell division and represses differentiation so mass of undifferntiated cells; high AU so defences supressed; gall is sink for carbohydrates so draws in photosynthate to grow
Rhodococcus fascians
Makes leafy gall
Linear plasmid - string of bacterial genes expressed in bacteria to control host development
Rhodococcus fascians lifecycle
Stage 1: Invades plant tissue
Takes nutrients and grows - Epiphytic phase
Endophytic - grows inside
Suppresses host defences
Population grows too big so no longer supported - change from biotrophic to necrotrophic to form gall
Stage 2: Gall forming phase
Make larger home for pathogen
Regulated by host C and N
Induces fasciation genes to synthesise CK
Pathogen knows when pop too big through monitoring of host C and N - know when ratio unbalanced
CKs
Plant growth regulators synthesised by plant or microbe
Needs to be degraded for responsive signal
Receptors to perceive synthesised CKs - activate set of genes
CK response: cell proliferation or defence
Imbalance of CKs detected by plants and triggers defence response
Pathogen manipulation of CK synthesis
How to make:
1. use ATP/ADP/AMP w another precursor - makes active CK then degraded
2. RNAs involved in protein synthesis - modified and broken down so releases active CK which is then degraded
Pathogens make methylated version of CK which is not made by plant - work well and as effective as CK
Too much CK = downregulated of plant made CK synthesis
Methylated version as these can build up as can’t be degraded by plant so builds up to form leafy gall
Plant defenes
Plant derived CK balances defence and susceptibility
Methylated CK activates other receptors and plant becomes more susceptible so ends up w leafy gall
Agrobacterium rhizogenes
Make rooty gall
Manipulates auxin metabolism
Nematodes
Animals that manipulate host development
Can manipulate meristem regulating peptides
Root knot
Invade plant tissue of root tip
Make feeding structure nodule
Enlarge host cells to feed nematode - conduit for nutrient flow towards nematodes
Cyst
Fragmentation of cell wall - broken connections
Giant cell to feed on
Syncytium - broken cell wall
Next to vascular system so nutrients flow in
AU and nematodes
Nem manipulate flow of PGRs and AU signalling
AU makes plants bigger so plants control this but nem can manioulate AU transporters
Nem can bind and enhance flow of AU into plant cells - metabolism and flow
Nem produce proteins to manipulate this
Plants produce peptides that diffuse between cells to control development - nem can produce same peptides
