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Plants

QuestionAnswer
Why are plant microbe interactions beneficial? -Essential for C and N recycling -Important for plant growth (water an nutrients) -Important for strengthening plant health
Why are plant microbe interactions detrimental? -Can be detrimental to plant health -Pose a threat to crop production -Pose a threat to natural ecosystems
Which plant pathogens are intracellular? Viruses
Which plant pathogens are extracellular? Bacteria, Oomycetes, Fungi and Nematodes
What are Saprophytes? What do they do? Why are they important? Bacteria and Fungi that feed off of dead plant (and animal) material by secreting enzymes to digest the matter and then ingesting it. Essential for N and C recycling.
What are Symbionts? Why are they important? Bacteria and Fungi which form mutualistic relationships with plants. Important for water/mineral uptake and also for N fixing.
What are mycorrhizae? What do they do? Fungi which associate with plant roots to promote water and mineral uptake. May also provide growth hormones and protect against pathogen attack. 460million years old.
What are the two types of mycorrhizae? Ectomycorrhizae and Endomycorrhizae
What do Ectomycorrhizae do? Forms sheath around plant root with hyphae emanating through soil to increase surface area available for water and mineral uptake. Penetrates between cells of cortex to for the Hartig Net which facilitates nutrient exchange.
What do Endomycorhizae do? Infect roots and penetrate root cell wall, branches within cells and forming arbuscular structures that provide nutrients. Hyphodium forms to attach fungus to plant, PPA alter plant cytoplasm prior to penetration by hyphae.
Give an example of: 1) An Endomycorrhizae 2) An Ectomycorrhizae 1) Pisolithus Tinctorius 2) Gigaspora Gigantae
What are Rhizobium? What do they do? Gram negative bacteria which fix nitrogen to ammonia using enzyme nitrogenase. Enzyme is only functional in aerobic conditions so root enzyme leghaemaglobin is used to tie up oxygen.
What percentage of crop loss in developing countries is due to disease? 40-50%
What is a faculative pathogen? Pathogen which attacks plant cells but can grow on its own.
What is an obligate pathogen? Pathogen which can only grow inside a specific living host.
What is a biotrophic pathogen? Pathogen which feeds on living plant tissue.
What is a necrotrophic pathogen? Pathogen which kills plant cells and then feeds on the dead matter.
What is a hemibiotropic pathogen? Pathogen which is initially biotrophic but becomes necrotrophic
How are viruses transmitted to new host plants? Persistence: seeds, plant debris from previous crops, vegetative propagation, grafting Mechanical: tools, machinery, handling. Specific vectors: insects, mites, nematodes, fungi, bacteria, aphids (injection with stylet)
Give two examples of plant viruses affecting the potato crop, what do they cause? Potato Virus Y causes stunting Potato Mop Top Virus causes spraing
What kind of pathogen is bacteria, Erwinia (Pectobacterium carotovora)? What does it infect? How is its transmitted? What kind of secretion system does it use? Necrotroph. Has a wide host range. Water/Soil borne but can be transmitted by insects. Type 2: secretes cell wall degrading enzymes (pectinases).
What kind of pathogen is bacteria, Pseudomonas Syringae? What does it infect? Where does it grow? How does it work? Hemibiotroph Narrow host range (tomato) Between plant cells (apoplast) Initially biotrophic, suppresses immune system by type 3 secretion that delivers proteins inside the living cells, later becomes necrotrophic, kills cells for food.
What kind of pathogen is bacteria , Agrobacterium Tumefaciens? What does it do? Biotroph. Injects DNA using type 4 secretion system, suppresses the immune system and modifies cells to produce tumors called galls.
Describe the nematode life cycle? Free-living juvenile penetrates root and migrates to vasculature and forms feeding structure (syncitium). Female grows eggs, dies and forms cysts to protect eggs.
Where do nematodes produce effector proteins? How do they secrete effector proteins? What are the functions of the proteins? Produced in oesophageal gland cells and screted through stylet. Effector proteins regulate: migration through root, initiation of feeding site and also suppress of host defences
What does fungus Fusarium graminearum cause in plants? What type of pathogen is it? What does it do? How is it toxic to humans? Wheat head blight. Necrotrophic ascomycete fungus that kills plant cells with mycotoxins. Accumulate in food.
Describe rice blast fungus. Magnaporthe oryzae. Biotrophic Ascomycete fungus. The major disease of rice causes 10-50 % losses of the rice crop. Air-borne disease which attack leaf (foliar) tissue.
What is late blight caused by? What plant does it affect? Why is it such a problem? Phytophthora infestans, hemibiotrophic fungus. Infects potatoes causes necrosis. Most serious potato disease, cost €7 billion per year and is a threat to global food security
What does PAMP stand for? Pathogen Associated Molecular Patterns
Describe the passive (constitutive) defense of plants against pathogens? Anatomical barriers, preformed inhibitors, antimicrobial proteins and compounds
What is PAMP triggered immunity? Recognition of PAMP by extracellular PRR's.
What defense responses are initiated in response to recognition of pathogen pattern? Antimicrobial Pathogenesis related proteins: transcript induced by path attack, PR2-PR3, PR4, attack cell wall. Antimicrobial compounds: phytoalexins induced locally. Structural Defenses: ligin synthesis, callose formed around penetration site.
What is effector triggered susceptibility? Pathogenic inhibitors of immune response by plants. Effectors that are released into cell. (Type 3 SS)
What is the hypersensitive response of plants? Up reg of PR genes, production of antimicrobial. localized programmed cell death
Created by: Laura Inglis