Breaking and entering: host penetration by the fungal rice blast pathogen Magnaporthe grisea

Fungal plant pathogens have evolved diverse mechanisms for penetrating into host plant tissue, ranging from entry through natural plant openings to various mechanisms of direct penetration through the outer surface. The filamentous fungus Magnaporthe grisea can cause disease on many species of the grass (Poaceae) family. The disease on rice, Rice Blast, is of enormous economic importance and biological interest. The mechanism used by this pathogen for breaching the formidable host surface barriers has been studied cytologically and genetically as a model for plant pathology, and represents a remarkably sophisticated achievement of nature. The single-celled appressorium of M. grisea acts as a vessel for the generation and application of perhaps the highest turgor pressures known. The fungus requires and utilizes melanin-derived, osmotically generated pressures estimated at 80 bars to drive an actin-rich cellular protuberance through the surface of a rice leaf or plastic coverslip.