A UDP-glycosyltransferase gene enhances resistance to Fusarium avenaceum in red clover

Root rot is an important red clover disease caused by Fusarium avenaceum . Severe attacks significantly reduce the persistence of this forage crop. In this study, we used contrasting accessions to identify important defense factors against the F. avenaceum pathogen initially using RNA-seq. We identified 251 genes that were uniquely induced in the more resistant accession Formica, including several receptor-like kinases and UDP-glycosyltransferases. Four candidates were shortlisted on the basis of their expression patterns and predicted defense-related functions for further evaluation in a new transient expression assay using red clover leaves. TpUGT89B1 and TpLRR-RLK most effectively reduced fungal colonization and were subsequently used in stable transformation in the background of the susceptible accession SW 1678002. Constitutive expression of either TpUGT89B1 or TpLRR-RLK significantly enhanced resistance to F. avenaceum , with TpUGT89B1 providing the greatest reduction in fungal biomass and disease symptoms. Sequence comparison and structural modeling revealed that TpUGT89B1 possesses the conserved GT-B fold and characteristic features of a plant family 1 UDP-glycosyltransferase. Homology-based STRING analysis, supported by RT‒qPCR, revealed that TpUGT89B1 is involved in flavonoid biosynthesis through its co-expression with TpCHS , TpCYP75B1 and TpFLS1 . Collectively, the results of this study provide integrated transcriptomic information and structural prediction of TpUGT89B1, suggesting that it functions in defense through glycosylation-associated specialized metabolism.