Mechanics of Invasive Fungal Growth and the Significance of Turgor in Plant Infection

Abstract

In many plant diseases, fungi execute direct cuticular penetration and then breach the epidermal cell wall. A mycelium is established by further invasive growth through host tissues. The role of specific exoenzymes in the disease process is still questionable, but mechanical aspects of invasion are well defined. Invasive growth by tip-growing hyphae is largely driven by the force available from turgor pressure, though cytoskeletal expansion may play a subsidiary role. The delivery of this force to the substrate in contact with the hyphal tip depends upon the interplay between turgor, the cytoskeleton, and processes that control wall-yielding; this is formalized in a novel mathematical model for plant infection. Empirical support for the model comes from studies on hyphal growth, and from experiments on appressorial development in the rice blast fungus Magnaporthe grisea. There is substantial evidence that turgor-driven invasive growth provides the link between melanin synthesis and pathogenicity in M. grisea.