Fusicoccin

Fusicoccin is a phytotoxic secondary metabolite produced by certain plant-pathogenic fungi of the genus Fusicoccum, most notably in species that infect woody plants. It is a diterpene glycoside and one of the best-studied fungal toxins that affect higher plants. The compound has played a key role in plant physiology research due to its pronounced effects on stomatal movement and cell elongation.

In plants, fusicoccin acts by forming a stable complex with 14-3-3 proteins and the regulatory domain of the plasma membrane H+-ATPase. This interaction locks the H+-ATPase in an active state, driving continuous proton extrusion at the cell surface. The resulting apoplastic acidification and hyperpolarization promote ion uptake, water movement into cells, and cell elongation. A prominent consequence is the rapid, sustained opening of stomata, which can lead to excessive water loss and wilting in infected tissues.

Symptoms in susceptible hosts include leaf curling, rapid stomatal opening, and dehydration-related wilting. Beyond its role as a disease factor, fusicoccin has been used as a valuable experimental tool to investigate the regulation of the plasma membrane H+-ATPase, membrane transport mechanisms, and the involvement of 14-3-3 proteins in plant physiology. Chemically, fusicoccin refers to a class of related diterpene glycosides, with fusicoccin A being a commonly studied member. Handling and study of fusicoccin require appropriate biosafety considerations due to its bioactive nature.