Endophytic mycobiont provides growth benefits via a Phenylpropanoid-Auxin axis in host plants

Beneficial association with symbiotic fungi helps improve the 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 endosphere during plant interaction and channeled the metabolic flux to phenylpropanoids and requisite secondary metabolites to promote plant growth. AR8 enabled biosynthesis of auxin improved root growth and provided an intrinsic source for long-distance signal that enhanced shoot biomass. Chemical complementation with p-coumaric acid restored the auxin signaling and enhanced growth in AR8-inoculated pal1 mutant plants, thus implicating such 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 phenylpropanoid pathway and auxin signaling in the AR8 symbiosis model.