Appressorium morphogenesis and penetration in rice blast fungus

Abstract The host tissue barriers mediate numerous, evolutionary adapted lines of defense to resist and endure environmental impacts and invading pathogens. In turn, the pathogenic microorganisms (e.g., fungi), when targeting “living sources of nutrition,” constantly develop diverse molecular and cellular mechanisms to subvert the tissue defense barriers. In this review, we discuss the infection pathways acquired by Magnaporthe oryzae, a rice blast fungus, to demonstrate the complicity of molecular evolution of the pathogen-to-host barrier interactions. M. oryzae initiates infection using a heavily melanized, dome-shaped structure known as the appressorium, a specialized cell structure, which generates turgor pressure to penetrate the leaf epidermis. How these events occur is still not completely understood. However, it is well-documented that appressorium structure is originated from the germ tube following spore attachment and germination on the host surface. This formation starts upon the tip of the germ tube intermits polar growth, hooks, and begins to swell. Then, the content of the spore is mobilized into the developing appressorium and a septum emerges at the neck of the appressorium. So, understanding of the molecular mechanisms driving the breach of host defense lines could shed light on the nature of pathogenicity of M. oryzae and lead to elaboration of new countermeasures to control the rice blast disease.