Nature Microbiol. 1, 16043 (2016)

Biotrophic and hemibiotrophic fungi love an alkaline environment, as it increases their infectious growth. In plants, numerous RALF (rapid alkalinization factor) peptides are involved as endogenous developmental regulators. One of their most striking effects is an increase in apoplastic pH. Antonio Di Pietro of the University of Córdoba, Spain, and colleagues show that, to infect more efficiently, fungi hijack this plant pathway by producing their own RALF peptides.

The root-infecting fungus Fusarium oxysporum causes wilt disease, leading to yield losses in many different crops. Using tomato and Arabidopsis, the authors show that Fusarium and other plant pathogenic fungi contain a functional homologue of plant RALF peptides. Infecting the host plant with a fungal strain lacking the peptide reduces external alkalinization and limits the pathogen virulence. Moreover, similarly to the endogenous peptides, the perception of fungal RALF by the plant is mediated by FERONIA, a multifunctional receptor-like kinase.

Fusarium gained the ability to activate a plant developmental pathway by acquiring or mimicking an alkalinization-inducing peptide, and uses it to enhance its own infectious growth by suppressing plant defences. This research could be used for increasing crop resistance to pathogenic fungi. It also highlights the often neglected role of pH in biological interactions, and further blurs the distinction between pathogen effectors and the more generic non-self signals known as MAMPs.