Plants, pathogens and puppets Flashcards
Food security – a global grand challenge
Magnaporthe oryzae is known to infect around 50 species of monocots including barley
In 1985 Magnaporthe oryzae made a host jump from a native South American grass species (probably Lolium perenne) to wheat
2016 saw an outbreak in Bangladesh, the first infection of wheat in Asia by M. oryzae
This year, the first outbreak in India was reported
Magnaporthe oryzae life cycle
Coniophore=spores for reproduction
osmotic pressure pushes a penetration hypha/peg with enzymes to loosed plant cell wall and causing physical damage.
Plant tactics are to just keep creating barriers so that invader eventually loses all of its energy.
It grows inside of plants cell as an invasive hyphae to then further colonise the tissue to then erupt a conidiophore.
runner hyphae. Maybe hyphae are bulbous as less cell wall exposing to the plant
Effectors have targets in host cells and some interfere with host cell immunity
Diverse pathogens (here bacteria and fungi) have many of the same effector targets in the host
Hosts use the same molecular mechanisms to combat invasion
pseudomonas bacteria has type three …
Fungi use effectors to break into the plant cell
All fungal cell walls are made of chitin. Fungi produce effector proteins containing LysM domains which bind chitin and “cloak” the invading fungus.
The M. oryzae protein Slp1 is one such effector.
Fungi use diverse strategies to invade plant hosts, but all use effector proteins.
Magnaporthe effector function in plants
BIC biotrophic interfacial complex (interface between plant and fungus)
Effectors are produced by the invading fungus to facilitate infection by making the environment inside the plant favourable for the pathogen
They accumulate at the Biotrophic Interfacial Complex (BIC)
A functional definition of effectors may embrace proteins, metabolites or even RNA
May act to evade host immune system or to reconfigure host metabolism
Crucial to understand course of infection
Fluorescent proteins can be used to show distribution of effector proteins during infection.
Fluorescent proteins can be used to show distribution of effector proteins during infection.
BAS4 labelled with green fluorescent protein
PWL2 labelled with red fluorescent protein (the BIC)
PWL2:FPs, but Not BAS4:FPs, Are Translocated into the Rice Cytoplasm. Yellow (overlapping of green and red) in merged images indicates BIC-associated cells.
delivery of stuff from fungal tip (BIC is similar to this does start at tip but then repolarisation of cells grow out and migrates the interface)
Magnaporthe oryzae makes both CYTOPLASMIC and APOPLASTIC effectors.
fungal cells seem to be highlighted in green. Fungal keeps cell membrane intact.
There are some effectors in apoplastic space to not be recognised, apoplastic effectors take over processes such as gene expression and how chloroplast works to have other effects.
Magnaporthe infection affects chloroplasts
once fungus is inside, chloroplasts are affected
Chloroplast behaviour is altered near infection sites
Chloroplasts, as the site of photosynthesis and phytohormone production, are precisely the kind of target we might expect for effectors
FACS analysis shows chloroplasts are reduced in size and fluorescence during infection
Yeast-2-Hybrid shows Magnaporthe effector Mep3 interacts with Psbp, a PSII component
Fluorescence imaging of chloroplasts for early detection of disease
Pre-lesion effects are detectable, by measuring chlorophyll fluorescence
Efficiency of PSII (Fv/Fm) and dissipation of energy as heat (NPQ) are altered in infection
Pseudomonas syringae and photosynthesis
The bacterial pathogen Pseudomonas syringae (pv DC300) suppresses photosynthesis prior to increased growth rate.
Red blobs are chloroplast after 8 hours there is already an infection.
Pv =pathovar is like the strain
hrp=harp mutant is a pseudomonas mutant of just one gene (more similar to control lost ability to suppress photosynthesis)
What does the harp protein do
Type III secretion system (T3SS)
a structure like a molecular syringe it is the type 3 secretion system/apparatus
The bacterial pathogen Pseudomonas syringae uses a type III secretion system to deliver effectors to the host cell
It is like a syringe, where the needle of the syringe is made of Hrp protein subunits
hrp mutants are unable to deliver effector proteins
hollow in middle to allow factors to be delivered and also has a needle-like pilus to deliver the effectors. the subunits that make up the system are made of the harp protein.
Figure 3 Representative EM images of PstDC3000ΔavrPto (pAVRPTO), immunogold-labeled with the HrpA (A) or HrpW (B) antibody or dual-labeled with HrpA and AvrPto antibodies (C) under the SA chase induction condition (18).
Immuno-gold labelling and Transmission Electron Microscopy (TEM) identifies effector proteins travelling through HrpA pilus. Long thing is the pilus for the type 3 secretion system. They use 2 different labels, an antibody to harp protein so for detection. Antibodies AvrPto an avirulence protein. The different sized balls are different spheres of gold just for determining the different between the antibodies as no fluorescence so size of gold particles helps us distinguish. A secondary antibody used in order to have a modular system and measure different things.
Small particles coat pilus and top have lots of AvrPto.
Photosynthesis is a target of plant pathogen effectors
ROS are detected by green dye. When plant cells set up a response they start to produce ROS. This is in the harper mutant that doesn’t affect chloroplasts whereas the image showing us the pseudomonas infection there is no ROS as the bacteria prevent the plant from making this.
Link photosynthesis and bacteria by using DCMU
Photosynthesis is a target of plant pathogen effectors
Pathogen effectors are targeted to the chloroplast
Early H2O2 signalling from the chloroplast to the nucleus
Summary
Gene for gene
Direct interaction / indirect (guard) interaction
Zig-zag model and its limitations
Effectors and plant effector targets
Co-evolution of host and pathogen
Durable resistance
Effector function in plants
M. oryzae-rice and P. syringae-Arabidopsis
