Lecture 11: Fungal Plant Pathogenesis Mediated By effectors

Question 1

Pathogenicity

Answer 1

The ability to cause disease

Question 2

Virulence

Answer 2

The quantifiable manifestation of pathogenicity

Question 3

Virulence factors

Answer 3

Molecules produced by the pathogen to aid in adhesion, colonisation, dissemination, survival and evasion of plant response

Question 4

Avirulence pathogen

Answer 4

Micro-organism that infects the host, but does not cause measurable damage to the host

Question 5

Resistance

Answer 5

When pathogen growth on or inside the host plant is limited, preventing the establishment of disease

Question 6

Tolerance

Answer 6

When infected host plants exhibit limited disease damage, despite a substantial pathogen load

Question 7

Susceptibility

Answer 7

Inability of a plant variety to restrict the growth and development of a pathogen, leading to a high disease incidence

Question 8

Compatible interaction

Answer 8

• Successful infection
• Disease development

Question 9

Incompatible interaction

Answer 9

• Successful plant defence
• No disease

Question 10

Effectors

Answer 10

Small proteins are delivered into the host plant to alter the host cell structure and function

Question 11

Hypersensitive response (HR)

Answer 11

Rapid localised cell death at the site of pathogen penetration, often associated with disease resistance

Question 12

Avirulence (Avr) gene

Answer 12

The gene that encodes an avirulence factor- causes avirulence in the presence of the corresponding R gene

Question 13

Virulence (avr) gene

Answer 13

Altered avirulence gene, no longer interacting with the plant R gene product. Disease and symptoms occur

Question 14

Avirulent pathogen

Answer 14

Any pathogen that harbours an avirulence gene whose product is recognised by a host that harbours the complementary resistance gene

Question 15

Co-evolution zig-zag model of plant-pathogen defence strategies

Answer 15

1. Plant pattern recognition receptors (PRRs) recognise pathogen Pathogen-associated molecular patterns (PAMPs), activating PAMP-triggered immunity (PTI)
2. Pathogen effectors interfere with PTI, if successful resulting in effector-triggered susceptibility (ETS)
3. Effector is recognised by the plant R protein, activating effector-triggered immunity (ETI)

Question 16

Neutral term

Answer 16

Not implying a negative or positive outcome of the disease interaction

Question 17

Effectors include

Answer 17

• Factors that help to translocate true effectors through host barriers
• Factors that elicit resistance response in the incompatible interaction
• Factors that allow pathogen to complete disease cycle once it has overcome plant immune system

Question 18

Magnoporthe oryzae effectors

Answer 18

• Hemi-biotrophic pathogen causing rice blast disease

Question 19

Biotrophic inter-invasion complex (BIC)

Answer 19

Specialised region of extrainvastive hyphal membrane matrix for fungal secretion

Question 20

Slp1 (apoplectic effector) of Magnoprthe oryzae

Answer 20

• Accumulates during early stages of infection at the rice-fungus interface
• binds to chitin to suppress chitin-triggered PTI

Question 21

AvrPiz-t (Cytoplasmic effector) of Magnoporthe oryzae effectors

Answer 21

• Target the rice R gene product Piz-t
• Plants lacking Piz-t are susceptible to the pathogen that carries AvrPiz-t

Question 22

Parastagonospora nodorum

Answer 22

Necrotrophic pathogen causing Septoria nodorum blotch in wheat

Question 23

SnToxA Effectors of Parastagonospora nodorum

Answer 23

Induces PCD in wheat that contains the Tsn1 dominant sensitivity gene
* Binds to chloroplast-localised protein ToxABP1, resulting in accumulation of reactive oxygen species followed by cell death

Question 24

SnTox1

Answer 24

• Apoplastic NE
• Protects against chitinases
• Induces pCD in wheat that contain the Snn1 dominant sensitivity gene