Detailed, no nonsense lecture notes the role of effectors in infection and the delivery systems pathogens use, thinking about common strategies employed by a variety of pathogens and thinking of the broader significance of studying plant pathology, including case studes on:
• The Magnaporthe-r...
Lecture 4 – plants, pathogens, and puppets
Objectives
• Discuss the role of effectors in infection and the delivery systems
pathogens use.
• Thinking about common strategies employed by a variety of pathogens.
• Thinking of the broader significance of studying plant pathology.
• The Magnaporthe-rice pathosystem (case study 1).
• The Pseudomonas-Arabidopsis pathosystem (case study 2).
Food security – a global grand challenge:
• Plant pathogens are responsible for 15 – 30 % loss of food crop yield and
are moving with climate change.
• About half the world rely on rice as a staple food and as populations rise, it
is estimated that yields will have to double in the next 40 years to
sustainably feed the increased population.
• Rice blast fungus (Magnaporthe oryzae) is the major pathogen of
cultivated rice globally and kills enough rice each year to feed 60M people
(Molecular Plant Pathology (2012) 13(4) 414–430, voted it most important
fungal plant pathogen)
• 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…
,Infection is strictly orchestrated.
, Magnaporthe effector function in planta:
• Effectors are produced by the invading fungus to facilitate infection by
making the environment inside the plant favourable for the pathogen.
• The 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.
Giraldo M., and Valent B. (2013) Nature Reviews Microbiology 11, 800–814
doi:10.1038/nrmicro3119: Use of effectors.
The use of live-cell fluorescence imaging as eukaryotic filamentous pathogens invade living
plant cells has generated a detailed picture of the focused secretory 'warfare' that occurs
between plants and potential pathogens, beginning even before the pathogen breaches the
host surface.
Fungi and oomycete pathogens use diverse biotrophic strategies to invade living plant cells,
but they all secrete a considerable range of effector proteins, including apoplastic effectors
that remain in the plant extracellular space and cytoplasmic effectors that move across the
plant plasma membrane into plant cells.
Effector secretion seems to be precisely controlled in time and space, as waves of effectors
are secreted at different invasion stages and effector secretion is targeted to specific
locations. Some effectors are secreted through appressorium pores before penetration and
others are secreted into specialized compartments at the biotrophic interface inside plant
cells.
After delivery into plant cells, cytoplasmic effectors target diverse cellular locations and
some even move into uninvaded plant cells, presumably to prepare these before invasion.
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