In summary, recent studies have allowed us to draw some firmer
conclusions regarding the infection of rice plants by the blast fungus
M. oryzae. It is now clear that surface attachment and germination
depends on coordination of the cAMP response pathway and
the Pmk1 MAP kinase signalling pathway, regulated by G-protein
signalling at the cortex of the developing fungal germ tube. This
is linked to cell cycle control and an S-phase checkpoint, which regulates
initial isotropic expansion during the first stages of appressorium
morphogenesis. A single round of mitosis in the germ tube is
necessary for appressorium maturation and autophagic cell death,
involving degradation of the three conidial nuclei, is essential for
appressorium function, with only a single nucleus remaining in
the appressorium as it develops. Turgor is then generated in the
appressorium by means of glycerol accumulation and, once a
threshold of appressorium turgor is achieved, cytoskeletal remodelling
occurs to initiate re-polarisation and plant infection.