EG 1&2

Question 1

are all microorganisms damaging to plants

Answer 1

no, some are pathogens but others can be beneficial

Question 2

examples of beneficial microorganisms to plants

Answer 2

nitrogen fixing bacteria allows plants to uptake nutrients (nitrogen) that would otherwise be more difficult/unavailable to it, bacillus thuringeinsis one of many pathogens used in bacteria (produces toxins against insects)

Question 3

how many microorganisms are available for biological control of pathogens against plants

Answer 3

60 bacteria strains, 60 fungi strains, 30 viral strains

Question 4

what are the 4 different types of pathogens

Answer 4

bacteria, fungi, virus, oomycete

Question 5

what are the 3 different lifestyles of pathogens and define each

Answer 5

biotrophs- live within host tissue and do not cause death, necrotrophs- kill cells and consume the contents, hemibiotrophs- switch between biotroph and necrotroph

Question 6

what is the ‘disease triangle’ composed of

Answer 6

host must be susceptible to pathogen, pathogen must be able to overcome host defensive mechanisms, environment must tip in favour of the pathogen

Question 7

blight causing pathogen and its optimal conditions

Answer 7

phytophtora infestans (pathogen of the great famine), high humidity and moderate temperature

Question 8

what are the 3 physical barriers in plants

Answer 8

epidermis (jigsaw-shaped cells in leaf epidermis), cuticle (layer on top of epidermis), cell wall

Question 9

what are the weaknesses to the physical barriers

Answer 9

stomata (natural openings on underside of leaf), wounding (by herbivores), insect feeding (penetrate plant tissue and either inject pathogens or allow them to enter)

Question 10

how do pathogens enter the plant

Answer 10

some pathogens make structures called appressorium which use high pressure to puncture the cell wall and enter while other pathogens secrete enzymes to digest this cell wall, other pathogens exploit the natural weaknesses of plants barriers such as entry through stomata or during insect feeding

Question 11

what are the properties of an immune response

Answer 11

detection of pathogen presence, recognition of specific pathogen, pathogen specific recognition (avoid auto-immune disorder - wrong response to infection), ultimate goal is molecular events to activate plant’s defence to prevent pathogen multiplying, spreading, or surviving

Question 12

what is the only type of immunity plants have

Answer 12

innate - do not need prior exposure to pathogen to be activated, plants have no ‘immune memory’ unlike animals

Question 13

what are the 2 types of immune response in plants and define each

Answer 13

PTI (pattern) - broad spectrum immune response (not pathogen specific), ETI (effector) - pathogen specific immune response

Question 14

what is a PAMP

Answer 14

pathogen-associated molecular pathogen, small molecular motif recognised by innate immune system needed for pathogen survival and infection, their pattern is foreign to host which allows for detection and prevents self-recognition (auto-immune disorder), eg. flaggelin and lipopolysaccharides

Question 15

what are PAMPs recognised by in plants

Answer 15

PRRs (pattern recognition receptors) extra-cellular or PAMP binding domain, specifically RLKs (receptor-like kinases) - present in ALL plant cells, fls2 is the PRR for the pathogen flagellin recognising flg22 peptide residue

Question 16

what is the series of molecular events downstream of PAMP recognition called

Answer 16

PTI (pattern triggered immunity)

Question 17

what is the workflow of phosphorylation downstream of PRRs (fls2)

Answer 17

-flagellin binds to fls2 induces interaction with BAK1
-interaction with intracellular RLKs
-phosphorylation of the intracellular RLKs
Results in a PTI response consisting of:
-activation of MAP kinase pathway
-activation of transcription factors and expression of PAMP induced genes
-phosphorylation of other proteins and production of reactive oxygen species
-CA2+ influx