Disease and Protection

Question 1

Reason behind the irish potato blight?

Answer 1

Phytophthora infestans is an oomycete fungus

Question 2

Why was Canola instantly wiped out upon cultivation in Australia?

Answer 2

Black-leg disease (Leptosphaeria maculans) that rots bottom section of crop

Question 3

Three methods to avoid black-leg spread

Answer 3

avoid inoculum (contamination), fungicides and plant resistance.

Question 4

Three aspects of the disease triangle?

Answer 4

Host plant must be susceptible
Disease must overcome immunity of plant
Environment must be in favour of disease

Question 5

Environmental factors affecting plant susceptibility?

Answer 5

Temperature, planting density, Pollution

Question 6

List the three stages of the zig-zag model

Answer 6

1) PAMP - triggered immunity (Pathogen Associated Molecular Markers). Plant detects presence of pathogen and releases defence (PTI)
2) Effector triggered susceptibility. Host immune system repressed by pathogen (ETS)
3) Effector triggered immunity. Plant fights back! resistance and avirulence genes are activated (ETI)

Question 7

What does LRR-RK stand for and how is it used?

Answer 7

This is leucine rich repeat receptor kinase and has large extracellular domain to recognise patterns of pathogen. and intracellular kinase domain to make action around the plant.

Question 8

What are PAMPs/MAMPs and what are they recognised by?

Answer 8

Pathogen/Microbe Associated Molecular Markers recognised by pattern recognision receptors (PRRs)

Question 9

What is the general shape of a PRR?

Answer 9

A question mark going through membrane

Question 10

An example of well studied PAMP?

Answer 10

Flagellin (protein found on flagella of bacteria) is recognised by FLS2 receptor on the extracellular side.

Question 11

Where else do we see this pattern recognition system?

Answer 11

Between plant and microbe symbiosis such as nitrogen fixation.

Question 12

Describe in detail the process of nodule formation of nitrogen fixing bacteria.

Answer 12

Bacteria release nod factors that closely resemble chitin.
These get recognised by a LysM domain which activates the intracellular kinase domain. In this case, this also leads to the activation of a second protein and eventually leads to a symbiotic relationship.

Question 13

What is a common step after the activation of the kinase domain?

Answer 13

A kinase cascade leading to transcriptional responses.

Question 14

Name three typical defence responses of plants to combat pathogens

Answer 14

Release of reactive oxygen species, production of polysaccharide callose as a temporary cell wall, increased stress hormone release (jasmonic acid)

Question 15

Two classes of chemical defences released by plants?

Answer 15

Phytoanticipins - preformed before pathogen is present
Phytoalexins - generated in response to microbe
Microbe can release enzyme to degrade these chemicals however.

Question 16

How did scientists show this response to disease is occurring at the epidermis?

Answer 16

They test an FLS2 mutant of arabidopsis with no receptors against a wildtype. They found when they sprayed the disease normally, disease was more prevelant in mutant since the immune response was not triggered. Yet, when the pathogen was injected past the epidermis, both plants reacted equally.

Question 17

How have scientists applied knowledge of Arapidopsis pattern recognition receptor (EFR) to tomato?

Answer 17

Can genetically engineer tomato to have this gene to produce EFR receptor and hence make tomato resistant.

Question 18

What would have been a valuable control for the addition of EFR gene to tomato to create resistance against bacteria?

Answer 18

Introduce them to fungi also to prove both are equally as susceptible and hence that this is a specific response.

Question 19

Define an effector

Answer 19

Small protein released by pathogen to suppress plant PAMP immune system - can act inside the host cell.