Abstract

Elucidating the material basis and molecular mechanisms of endophytic fungal polysaccharide-mediated promotion of plant secondary metabolism is key to understanding endophyte–host interactions. Here, we found that crude exopolysaccharide (CEP) from endophytic fungus Fusarium solani CL105 promoted flavonoid biosynthesis in Scutellaria baicalensis seedlings, with CEP-0.3 as its major bioactive component. Subsequently, methylation and NMR analysis revealed that the backbone of CEP-0.3 consisted of (→2)-α- d -Man p -(1→), (→3,6)-β- d -Gal p -(1→), and (→4)-α- d -Man p -(1→) units, with β- d -Gal p -(1→) and α- d -Glc p -(1→) as terminal residues. Transcriptome analysis revealed that CEP-0.3 induced the expression of genes involved in GA/ABA biosynthesis ( CPS , CYP701 , KOA , GA3ox , GA2ox , GA20ox , NCED , ABA2 , AAO3 , CYP707A ) and MYB transcription factors ( SbMYB5 , SbMYB11 , SbMYB13 , SbMYB330 ), thereby upregulating core flavonoid biosynthetic genes ( PAL , C4H , CHS , CHI , FNS , F6H ) and ultimately promoting flavonoid synthesis in S. baicalensis . These findings demonstrate that endophytic fungal exopolysaccharides represent a promising approach for sustainable S. baicalensis cultivation and biotechnological production of pharmaceutical flavonoids.