P-260 - Root terpenoids: the hidden part of plant defense in the case of M.truncatula and the root pathogen A. euteiches

Plants produce a wide variety of secondary metabolites through specialized and species-specific metabolic pathways. Among these, terpenoids constitute the largest group of specialized metabolites, playing crucial roles in development, adaptation to external cues, and offering antimicrobial properties. By combining transcriptomics and metabolomics approaches, we are reporting the discovery and functional analysis of two terpene synthases (TPSs), MtTPS10 and MtTPSX, which are upregulated following infection with Aphanomyces euteiches in the roots of two Medicago truncatula ecotypes, A17 and B21, respectively. The TPSs are implicated as being responsible for releasing a complex blend of sesquiterpenoid phytoalexins mediating plant defense. Heterologous expression in yeast revealed that MtTPS10 catalyzes the formation of himachalol from farnesyl diphosphate (FPP) as its primary sesquiterpene product. In contrast, MtTPSX catalyzes the formation of copaene from FPP as the most abundant sesquiterpenoid. The volatile terpenes of these two TPSs exhibited antimicrobial activity against A. euteiches. Consequently, M. truncatula plants expressing either MtTPS10 or MtTPSX were found to be resistant to A. euteiches infection, while the respective mutants displayed an increased susceptibility to the pathogen. These findings shed additional light on legume resistance to root rot caused by A. euteiches and highlights a potential target for breeding durable, disease-resistant legume cultivars.