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The molecular biology of appressorium turgor generation by the rice blast…

- - - - onset of melanin
    - - tretraspanin
        
        controlling translation of
        turgor into physical force for penetration hypha production
    - - penetration hyphae emergence
  - - - genes
        encoding enzymes of the biosynthetic
      - metabolic pathways of the conidial storage product
  - - - synthesized from
        storage carbohydrates – NADH-dependent glycerol-3-phosphate dehydrogenase and NADPH-dependent glycerol dehydrogenase
    - - activated during the onset of turgor generation
- - - - Within 4 h, the germ tube starts to swell at its apex, and flattens against the surface of the rice leaf
        
        The germ tube apex then develops into a swollen
        dome-shaped cell, called the appressorium
  - - - are unable to accumulate cAMP, do not form appressoria
        
        subject to frequent reversion by a second-site mutation in the regulatory subunit of PKA (cAMP-dependent protein kinase A)
        
        which leads to cAMP-independent triggering of PKA and restoration of appressorium development
    - - form small, mis-shaped
        and non-functional appressoria
    - - A MAP kinase (mitogen-activated protein kinase) cascade involving the Pmk1
        MAP kinase is required for the production of appressoria
  - - - The process of appressorium morphogenesis is tightly coupled to cell
        division
  - - - Mutants (non pathogenic) because they cannot produce appressoria
        
        That lack melanins are due
        to mutations in gene-encoding enzymes in the dihydroxynapthalene melanin biosynthetic pathway
        
        And are readily identified identified in M. grisea because of alteration in the colour of the
        fungus, which is normally grey
        
        buf1 mutant
        
        mutation of a gene encoding dihydroxynapthalene reductase, and it was so called because of the buff colour of mutants lacking this enzymatic activity
        
        M. grisea RSY1 gene
        
        encodes scytalone dehydratase, and mutants are identified because of their pink colour
        
        mutations in a polyketide synthase encoded by the ALB1
        gene,
        
        , lead to an albino mutant phenotype
- - - - Accumulation of high concentrations of glycerol (vapour-pressure psychrometry)
        
        Generation of substantial turgor pressure
      - appressorium accumulate de novo from storage product in conidia
        
        because on the leaf surface, there are free water, no external nutrient, glycerol and other solutes
        
        conidia analysis : accumulate lipids, glycogen and disaccharide trehalose
- - - - non-pathogenic
        
        2 trehalose-encoding genes
        
        NTH1
        
        neutral Trehalose
        
        highly expressed during conidiogenesis and spore germination
        
        :small_red_triangle:NTH1 has reduced virulence
        
        decreased ability to form invasive hyphae
        
        TRE1
        
        responsible for the production of the main trehalose activity during spore germination
        
        :small_red_triangle:TRE1 produce rice blast symptoms similar to wild-type
      - appresorium turgor pressure affected
      - pleiotropic effects
        
        occurs when one gene influences two or more seemingly unrelated phenotypic traits.
        
        Unable to grow on glucose or nay other rapidly fermentable carbon sources
    - - Unable to grow on glucose due to absence of T6P synthase activity leading to uncontrollable inflow of glucose into glycolysis
        
        Rapid utilization of ATP and drop of phosphate elevels
    - - Yeast unable to grow on glucose under any conditions because glucose has now become toxic
      - M.grisea glucose utilization can be restored using alternate carbon sources and complex nitrogen sources
      - M.grisea unable to grow on lipids and acetate; gluconeogenesis may also be affected by the loss of T6P synthase activity
  - - - Trehalose accumulates as an accesory-compatible solute in the appressoria
      - Sugar signalling role T6P synthase is essential for the regulation of appressoria turgor generation in M.grisea
- - - - activation of the glyoxylate shunt
      - gluconeogenesis
  - - - Mutants lacking the ICL1 gene encoding isocitrate lyase
        
        spore germination was retarded
        
        subsequent germ tube extension and appressorium
        morphogenesis
        
        ICL1 gene expression
        
        appressorium morphogenesis
        
        penetration peg
        
        invasive growth
        
        alternative pathways
      - temporal regulation effect on the development of
        appressorium
      - glucose-deficient environment
    - - appressorium-mediated plant infection
        
        antracnose
        fungus
        
        Colletotrichum lagenarium
        
        melanin-pigmented appressoria
        
        fatty
        acid β-oxidation
  - - - encoding isocitrate lyase
      - reduce in virulence due to a temporal regulation effect on the development of appressorium