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Genome-wide functional analysis reveals that infection-associated fungal…
Genome-wide functional analysis reveals that infection-associated fungal autophagy is
necessary for rice blast disease
Discussion
Autophagy is a cell survival response that is triggered by starvation stress, used to recycle cytoplasm, organelles, and protein within cells
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In this research, the results demonstrated that autophagosomes are enriched in conidia as soon as they begin to germinate, less than an hour after landing on a rice leaf surface.
MoATG1 gene was independently identified as a differentially expressed gene during appressorium formation and shown to be necessary for pathogenicity
The large burst of autophagic activity continues in the conidium until it collapses and undergoes cell death
Autophagy also occurs in,the appressorium during its development and maturation.
Autophagosomes and are highly enriched in appressoria and a large central autophagic vacuole acts as the lytic compartment in maturing appressoria, consistent with previous studies of lipolysis during appressorium formation
Autophagy is therefore necessary for programmed cell death in the conidium and for differentiation and
active growth in the appressorium.
Autophagy is up-regulated when the nutrient supply is insufficient to meet cellular energy demands and when cells are exposed to different forms of stress
Autophagy protect cells from death in a variety of eukaryotic organisms but autophagy has also been shown to be a contributing factor in cell death
indicating that a nonapoptotic
programmed cell death pathway exists in eukaryotes that is dependent on autophagy genes
M. oryzae can spatially regulate autophagy in such a way that it is necessary both for conidial cell death and also for maturation and differentiation of functional appressoria
Induction of autophagy during infection-related development is developmentally regulated and requires the Pmk1 MAP kinase kinase
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Purpose of authophagy is to fuel infection-related development in the absence of exogenous nutrients before entry into the plant
In conclusion,the absence of any component of the autophagic machinery is sufficient to prevent both conidial collapse and appressorium-mediated plant infection
TOR kinase plays a role in the initiation of infection-associated autophagy and also have potential interplay with cAMP-dependent protein kinase A signalling
Necessary for appressorium
morphogenesis in M. oryzae,
In S. cerevisiae, protein kinase A and the Sch9 kinase, for instance, cooperatively regulate induction of autophagy.
2nd Part
Major aim
To test whether infection-associated autophagy is a selective or non selective process that cannot be determined by analysis of MoATG8
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Deletion of any of the 16 gene products necessary for macroautophagy rendered fungus unable to cause blast disease
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Induction of autophagy
Multiprotein regulatory protein complex Atg13 with Atg17, Vac8 & other proteins activate the Atg1 in protein kinase S.serevisiae
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Deletion of any of the 6 specific genes associated with pexophagy or mitophagy did not affect fungal pathogenicity
Thus, these selective forms of autophagy are therefore not necessary for plant infection
The significance of peroxisome biogenesis to appresorium function & fatty acid-oxidation to appresorium physiology in subsequent stages of plant tissue colonization following breach of the cuticle
This study demonstrates that the Cvt pathway, as defined in S.cerevisiae is absent from M.oryzae providing further evidence that it is restricted to yeast and not present in multicellular filamentous fungi
We have provided the first genome-wide analysis of autophagy in a filamentous fungus and have validated the importance of nonselective autophagy in the establishment of plant disease by M. oryzae
Controlling the initiation of fungal autophagy may provide an effective target for development of new and novel antifungal strategies, given the fact that the plant infection process is so sensitive to perturbation of this process
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Introduction
plant pathogenic fungi
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structures, known as appressoria, a feature of some of the most important cereal pathogens
Appressoria
dome-shaped, single-celled structures
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formed following germination of 3-celled fungal spore, called conidium, which attaches tightly to hydrophobic rice leaf surface
Hydrostatic turgor
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layer of melanin in appressorium cell wall prevents efflux of glycerol allowing turgor to increase to level sufficient to rupture plant surface
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Germination
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one of resulting daughter nuclei migrates into incipient appressorium while other migrates back into conidium
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