seminar 1: Rolfe Flashcards
what does clubroot/ P.brassicae infect?
brassicas causing them to wilt and yield to decrease
what is oil seed rape often grown on rotation with?
wheat
what is is oil seed rape/canola worth in UK and US?
£700 million
$650 million
how much is canola estimated to contribute to canada’s economy annually?
$15bn
where is clubroot mainly found? (8)
- UK, mainly scotland
- Europe
- Asia
- Africa
- N and S America
- New Zealand
- Australia
- Canada
roughly what % scottish soil is infected with clubroot?
50%
clubroot can cause significant yield loss
a) how much is lost per 1% infected crop in UK
b) how much oil seed rape is lost in Australia?
c) what did yields in household plots in Nepal fall from and to?
a) 0.03t/ha
b) 1.6t/ha
c) 5000kg to 300kg
why is clubroot control difficult? ()
- produces soil borne spores lasting 20 years
- limit crop rotation effectiveness by infecting weedy brassicas
- spread by contaminated soil
- spread by flood in low point of field
- no effective chemical controls
- limited resistant varieties
what did Alberta uni find about brassica in early 2000s?
- grow brassica without rotation which is unsustainable
- so clubroot rapidly spread in the area
what is P.brassicae as it is not a bacterium?
eukaryote and often classed as protist
- obligate biotroph
what does it mean if are an obligate biotroph?
can only grown it on a living host
what are the 6 things a pathogen needs?
infect host evade host defences move find home- gall obtain nutrients reproduce
what do clubroot spores germinate in response to?
plant derived signals
what kind of soil is clubroot often found in and what enables this?
wet soil
has flagella
what are the brief stages of clubroots lifecycle? 7()
- spore in soil divides to become primary zoospore
- forms primary plasmodium
- infects root hair and divides to form zoosprangium
- forms secondary zoospore which can move into cortex or infect other root hair cells
- secondary zoospore moves into cortex forming secondary plasmodium
- gall formation occurs and cortical infection
- more spores produced and tissue degraded
give 3 points about galls?
- 1 can produce millions of spores
- strong sinks for carbohydrates, reducing yield
- disrupt water relationships leading to wilting and death as root system function lost
what can understanding gall formation lead to ?
routes to limit losses
what may be an issue with using Arabidopsis as a model plant?
not all brassicas are the same and its a lot smaller than oil seed rape
where do galls tend to form?
in the hypocotyl and start of root tissue
what did Devos et al claim to wrongly discover? what was wrong with it?
that cytokinins trigger cell division in root cortex forming a de novo meristem
- cytokinins important in cell division but dont form new meristems
what does CYCB1:GUS allow?
- 12 days after infection what can be seen in the infected plant?
cell division to be visualised
- lots of cells stained as protein is made
plants and eukaryotes have the same cell cycle but what differs?
regulators
what is the vascular cambium? (4)
- meristem that divides during secondary thickening
- gives rise to vascular system
- xylem produced on the interior
- phloem produced on the exterior
if cross section the plant horizontally how can you see the hypocotyl growing
outwards but not elongated
what is the VC stimulated by and what can you see in infected plants stained with CYCB1:GUS?
clubroot infection
- more blue cells stained and tissue swelling
- VC not as uniform
- cells containing plasmodia make spores
- islands of xylem and phloem made
- integrity lost
what is aintegumenta?
- what does it show in clubroot infected plants?
genetic marker for meristematic activity and is switched on in meristematic cells
- cells have swollen and are pushed around, distorting the VC
how does clubroot cause gall formation? (4)
- rates of cell division increased as consequence of VC activation
- no de novo meristem formation
- pathogen hijacks host developmental pathways and existing VC
- gall formation occurs in secondary thickening tissue
what can be concluded about xylem and phloem production in infected plants?
- xylem formation/xylogenesis strongly repressed early on
- results in wilting
- phloem production maintained or stimulated to provide sugar and amino acids to biotroph
by hijacking the VC activity what does it mean for the fate of the cells coming out of it?
altered
how may different gall types be formed?
by altering the amount of auxin and cytokinins
describe the gall forming disease:
a) A.tumefaciens
b) R.fascians
a) inserts T-DNA into plant genome
synthesises cytokinin and auxin, stimulating undifferentiated gall formation
b) synthesises auxin and cytokinin causing leafy gall to form
what did Dekhuijen claim and what was the very weak evidence?
claimed P.brassicae can synthesise cytokinins and that cytokinin responsive genes are activated in clubroot infected plants
what did siemens claim?
plants expressing cytokinin oxidase show tolerance
what happens to host cytokinin synthesis and gene expression during gall formation and 4 specific examples?
repressed
- IPT3
- IPT5
- LOG
- CYP735A1/2
from which 2 routes can cytokinin synthesis occur using?
tRNA
DMAPP
what are the 4 active cytokinins?
iP
tZ
DZ
cZ
what are the 4 stages of cytokinin synthesis?
2 synthetic routes-> to make precursors -> to make active cytokinins -> are degraded/conjugated
what happens to cytokinin content and responseive gene expression in infected tissues?
falls, downregulated
gene expression is induced
if clubroot is making cytokinin is it enough?
not enough to rescue mutant, not enough to drive gall formation
- too little too late to make VC
what does the fact cytokinin gene expression is induced in infected mutant plants support?
that P.brassicae does produce cytokinin
what does cytokinin play a role in?
gall formation and pathogen development
a) what 3 things were done when clubroot genome was sequenced?
b) what was found?
a) - coding region identified with bioinformatics and RNA sequencing
- identified gene function with bioinformatics
- looked at what pathways present/absent
b) unique new class of transporter found
half prokaryote transporter linked to half eukaryote transmembrane
what happens if we mutate genes associated with sucrose transport or if we mutate those associated with phloem development?
- slow disease development
- speed up
what do mutations in each reduce?
- phloem
- sugar transport
- C + N supply
- C supply
what does the phloem provide to allow for clubroot to maintain phloem development?
source of N (amino acids)
source of carbohydrate (sucrose)
what needs to be done to breed the next generation of clubroot resistant crops?
quantify resistance in existing plants
