O-Glycosylated expansin ThSWO condensates drive Trichoderma harzianum attachment to rice root during the colonization process

Abstract

Expansins and lectins facilitate microbial colonization, but their collaborative mechanisms across different colonization stages remain unclear, and fungal root attachment via these proteins requires further exploration. This study proposes a fungal early colonization hypothesis: Trichoderma harzianum uses the ThSWO-ThFFSL complex to promote hyphal attachment to rice roots. The results show that ThSWO loosens rice cell wall cellulose and forms biomolecular condensates via its intrinsically disordered region (IDR) and extensive O-glycosylation. These condensates specifically recruit the fungal fucose-binding lectin ThFFSL through fucose residues, and both colocalize in root surface cell wall crevices. After localization, ThFFSL guides hyphal growth and enhances adhesion, promoting fungal attachment within the crevices. Postattachment, T. harzianum secretes an O-glycosidase to deglycosylate ThSWO, dissociating the complex and mitigating root cell wall damage. Colonization assays confirm that ThSWO-ThFFSL synergy is crucial for efficient colonization. This study reveals an early attachment phase in fungal colonization driven by protein condensates and glycosylation modifications.