Living organisms are part of a highly interconnected web of interactions, characterised
by species nurturing, competing, parasitizing and preying on one another. Plants have
evolved cooperative as well as defensive strategies to interact with neighbour organisms.
Among these, the plant-fungus associations are very diverse, ranging from pathogenic to mutualistic.
Our current knowledge of plant-fungus interactions suggests a sophisticated coevolution
to ensure dynamic plant responses to evolving fungal mutualistic/pathogenic strategies.
The plant-fungus communication relies on a rich chemical language. To manipulate the plant
defence mechanisms, fungi produce and secrete several classes of biomolecules, whose modeof-
action is largely unknown. Upon perception of the fungi, plants produce phytohormones
and a battery of secondary metabolites that serve as defence mechanism against invaders or to
promote mutualistic associations. These mutualistic chemical signals can be co-opted by
pathogenic fungi for their own benefit.
Among the plant molecules regulating plant-fungus interaction, phytohormones play a critical
role since they modulate various aspects of plant development, defences and stress responses.
Intriguingly, fungi can also produce phytohormones, although the actual role of fungalproduced
phytohormones in plant-fungus interactions is poorly understood. Here, we discuss
the recent advances in fungal production of phytohormone, their putative role as endogenous
fungal signals and how fungi manipulate plant hormone balance to their benefits.