The fusicoccin story revisited.

Fusicoccin (FC) is one of the most studied fungal metabolites to date. The finding that the plasma membrane H+-ATPase in combination with 14-3-3 proteins acts as a high-affinity receptor for FC was a breakthrough in the field. Ever since, the binding of FC to the ATPase-14-3-3 receptor complex has taken center stage in explaining all FC-induced physiological effects. However, a more critical review shows that this is not evident for a number of FC-induced effects. This review challenges the notion that all FC-affected processes start with the binding to and activation of the plasma membrane ATPase, and raises the question of whether other proteins with a key role in the respective processes are directly targeted by FC. A second unresolved question is whether FC may be another example of a fungal molecule turning out to be a 'copy' of an as yet unknown plant molecule. In view of the evidence, albeit not conclusive, that plants indeed produce 'FC-like ligands', it is worthwhile making a renewed attempt with modern improved technology to answer this question; the answer might upgrade FC or its structural analogue(s) to the classification of plant hormone.