19. Filamentous plant pathogens Flashcards
Define filamentous plant pathogen
1
Plant pathogens that grow hyphae. These make up mycelium that manipulate the plant immune system
What are the 3 groups of filamentous plant pathogens?
2
2 fungal groups: Ascomycetes and Basidiomycetes
1 protist group: Oomycetes
**Even though oomycetes sound very fungee, they are not **
What are the characteristics of the 3 main groups of filamentous plant pathogens?
3
Basidiomycetes have club-like spores, whereas ascomycetes have sac-like spores. They both have chitinous cell walls, variable ploidy in their hyphae and spores. Spores are aerial, and have septate hyphae. Mitochondrial cristae are plate-like.
Oomycetes have cellulose cell walls, 2n hypheploidy and sporeploidy, and are adapted to spread via water with zoospores. They have aseptate hyphae. Mitochondrial cristae are tubular
How prevalent are filamentous plant pathogens
5
The top most prevalent crop and tree pathogens
What are our 3 main strategies for protecting against filamentous plant pathogens?
6
- Resistance breeding programmes (very attractive but takes a long time and will eventually be susceptible to resistance)
- Agrochemicals - like respiratory or biosynthesis inhibitors (however, these provide natural selection for resistant pathogens)
What type of diseases do oomycetes cause?
blights and blisters
grows in humid environments
e.g., Hpa and white blister
Describe downy mildew
8
Hyaloperonospora arabiopsis
Causes downy mildew
Can suppress immunity in any haustoriated cells by growing between cells, and the use of the PR1 promoter
Different A. thaliana ecotypes recognise different Hpa isolates, and therefore will have different Avr effectors
Describe white rust/blister
9
Albugo candida
Obligate biotroph, and forms white blisters on the lower side of the leaves
Several races
It is able to support co-infection with non-adapted pathogens. Albugo-infeccted tissues will often be infected by non-adapted pathogens due to their reduced production of antimicrobials
What do ascomycetes cause?
10
Blasts, wilts, molds and mildews
Describe fusarium wilt
11
Fusarium oxysporum
A soil-borne pathogen
Enters via the root, and colonises/blocks the xylem. Causes wilt by impacting water transport
Has host-specific strains.
Has mobile pathogenicity chromosomes that undergo HGT, and contain all of the effector-encoding genes
Descrobe powdery mildew
12
Blumeria graminis
An obligate biotroph that feeds only on epidermal cells
Produces white, asexual conidiaspores
Genome of 120Mbp, but has undergone extensive gene loss due to its obligate status
Has the Susceptibility gene (S), Mlo, which is essential for powdery mildew infection, and confers durable resistance to plant immunity
What do basidiomycetes cause?
12
Smuts, rusts and rots
Describe corn smut
13
Ustilago maydis
Smuts will sporulate in the flowers of grasses
They have a very complex life cycle that involves the formation of tumours on the corn, which rupture and spread teliospores. These then germinate to produce haploid cells
These haploid cells come together to form dikaryotic (n+n) filaments which then infect tissue, and grow towards the flower to cause disease
They have apoplastic effectors, including Pep1, which inhibts host peroxidase, and Pit2, which inhibits host proteases
They have host-cytoplasmic effectors, including See1, which causes tumours, and Tin2, which weakens lignin production in the plant, and Cmu1, which prevents the plant production of salicylic acid
Describe wheat stem rust
14
Puccinia graminis
Thought to have co-evolved with the wild grasses, and to be as old as wheat domesticaiton
Humanity’s ‘oldest enemy’
Has a complex life-cycle, involving the infection of both and barberry for different parts of the lifecycle
Norman Borlaug was the father of the green revolution, and developed semi-dwarf, high-yield, disease-resistant, wheat varieties
Spread back to Uganda in 1999 and UK in 2013
