Endophytic mycobiont provides growth benefits via a phenylpropanoid-auxin axis in host plants.

Beneficial association with symbiotic fungi helps improve growth and fitness in most land plants and shows great potential as biofertilizers in precision agriculture. Here, we demonstrated that a root fungal endophyte, Tinctoporellus species isolate AR8, enabled yield improvement in Brassicaceae leafy green choy sum (Brassica rapa var. parachinensis). Mechanistically, AR8 colonized the root cortex/endosphere and channeled the metabolic flux to phenylpropanoids and requisite secondary metabolites to promote plant growth. AR8-assisted biosynthesis of auxin improved root growth and provided an intrinsic source for long-distance signaling that enhanced shoot biomass. Chemical complementation with exogenous p-coumaric acid restored auxin signaling and enhanced growth in AR8-inoculated pal1 mutant plants, thus implicating such a phenylpropanoid-auxin nexus as a pivotal regulator of symbiotic plant growth. Comparative metabolomics established hydroxycinnamic acid and p-coumaric acid as major plant-growth-promoting hubs that bridge the phenylpropanoid pathway and auxin signaling in the cross-kingdom AR8 symbiotic interaction model.