L7 - cause dis

Question 1

Rust fungi caused by

indirect/direct germination ?

Answer 1

uromyces viciae-fabae

indirect germination

Question 2

Leaf blast spot caused by

indirect/direct germination ?

Answer 2

Magnaporthe oryzae

Direct

Question 3

Infection via adhesion to leaf surface + spore formation

steps

Answer 3

1. initial attachment to surface via hydrophobic interactions
2. spore imbibition - absorb water, swell - rounded
3. adhesion pad formation - prod of carbs + glycoproteins - some enzymatic degration of surface e.g. by cutinases
4. Germ pore swellying + lysis - lysed pore materials onto leaf surface
5. Germ tube formation - contacts leaf surface + grows - ECM carbs + glycoproteins

appressorium

Question 4

appressorium discuss

Answer 4

high pressure can penetrate plastic! 8MPA
appressorium wall has melanin - seal +strengthen - accumulation of glyerol deal w/ osmotic stress

cyclic AMP signalling req for appressorium formation

Question 5

albino mutant of melanin:

Answer 5

cant acc glycerol

collapse under osmotic stress

Question 6

mutant of melanin can still be pathogenic - exmaple

Answer 6

Rice Brown Spot
requires cutinase

penetration of plant via enzymatic and mechanical processes

Question 7

biotrophs obtain nuts via

Answer 7

formation of haustoria 
haustoria have 
- ATPase to create proton gradient 
- AA/sugar proton symport 
e.g. HXT1 in uromyces viciaefabae

Question 8

describe root infection

Answer 8

use chemical/electrical signals
zoospores move towards root by chemotaxis/elecrotaxis (oomycetes)
spores/sclerotia germinate + grow hyphae by chemotropism

Question 9

decribe shoot infection

Answer 9

spore(true fungi) or sporangia (oomycete) stick to leaf surface + germinate
germ tube penetrated leaf - through natural opening (stoma) / directly through epidermis
hyphae colonise host tissue

Question 10

pathogens can harm by

Answer 10

produce toxins
damage cell intergreity 
interfere with processes 
produce effectors
steal nutrients 
abnormal development - produce hormones

Question 11

Decrribe direct germination

Answer 11

germinate
form appressorium
+ directly infect epidermal cells

Question 12

Describe indirect germination

Answer 12

grow over leaf surface
locate stoma
from appresorium
grow through stoma

Question 13

fungal haustoria referred to as

Answer 13

‘hidden robbers’

Question 14

haustoria symport in biotrophs example

Answer 14

HXT1 sugar transporter with specificity for D-fructose and D-glucose