The fungal metabolite 4‐hydroxyphenylacetic acid from Neofusicoccum parvum modulates defence responses in grapevine
Résumé
In a consequence of global warming, grapevine trunk diseases (GTDs) have become a
pertinent problem to viticulture, because endophytic fungi can turn necrotrophic
upon host stress killing the plant. In Neofusicoccum parvum Bt‐67, plant‐derived
ferulic acid makes the fungus release Fusicoccin aglycone triggering plant cell death.
Now, we show that the absence of ferulic acid lets the fungus secrete 4‐
hydroxyphenylacetic acid (4‐HPA), mimicking the effect of auxins on grapevine
defence and facilitating fungal spread. Using Vitis suspension cells, we dissected the
mode of action of 4‐HPA during defence triggered by the bacterial cell‐death
elicitor, harpin. Early responses (cytoskeletal remodelling and calcium influx) are
inhibited, as well as the expression of Stilbene Synthase 27 and phytoalexin
accumulation. In contrast to other auxins, 4‐HPA quells transcripts for the auxin
conjugating GRETCHEN HAGEN 3. We suggest that 4‐HPA is a key component of
the endophytic phase of N. parvum Bt‐67 preventing host cell death. Therefore, our
study paves the way to understand how GTDs regulate their latent phase for
successful colonisation, before turning necrotrophic and killing the vines.
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