Role of terpene synthases in the defense of Medicago truncatula against Aphanomyces euteiches
Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
Final Report Abstract
Plants interact with a variety of organisms, including pathogens such as the oomycete Aphanomyces euteiches, which causes root rot in legumes. Early contact of Medicago truncatula roots with A. euteiches zoospores leads to enhanced expression of genes encoding terpene synthases (TPSs). Among them, MtTPS10 was identified as a multiproduct sesquiterpene synthase that is expressed in roots only after contact with oomycete zoospores. Products of MtTPS10, such as the major compound himachalol, contribute to the resistance of M. truncatula roots to A. euteiches but are subsequently modified in planta. Therefore, the role of a previously identified cytochrome P450 enzyme (CYP-A) in the conversion of himachalol was investigated. Co-cultivation of yeast strains expressing MtTPS10 and CYP-A yielded oxidized sesquiterpenes; however, analysis of their function in planta using cyp-a mutant plants is still pending. With respect to TPSs induced after root inoculation with A. euteiches, a previously uncharacterized TPS, MtTPS25, was found to be expressed in a particular M. truncatula ecotype (line 368) that is highly resistant to infection and completely lacks MtTPS10 expression. Expression of MtTPS25 was compared with that of MtTPS10 (in the reference line Jemalong A17 and in line 368) and characterized in detail, for example through promoter-swapping experiments. We also demonstrated a functional role for MtTPS25 in line 368 in mediating defense against A. euteiches. Silencing MtTPS25 via an RNAi approach in transiently transformed roots led to reduced MtTPS25 transcript levels, diminished emission of its major product α-copaene, and increased susceptibility to A. euteiches. These findings support the hypothesis that MtTPS25 contributes to the immunity of M. truncatula line 368. To test whether the transgenic expression of MtTPS10 or MtTPS25 enhances resistance of potato against Phytophthora infestans, both genes were constitutively expressed in stably transformed potato plants. Phenotypic analyses revealed no differences between transgenic lines and wild-type or empty-vector controls under standard growth conditions, but the transgenic plants emitted additional sesquiterpenes. In MtTPS10-expressing lines, a single sesquiterpene alcohol absent from wild-type plants was detected, whereas MtTPS25-expressing lines produced several additional sesquiterpenoids. Surprisingly, overexpression of MtTPS25 resulted in greater P. infestans biomass accumulation than in wild-type plants, whereas overexpression of MtTPS10 decreased P. infestans biomass. These results indicate that TPS overexpression is a promising strategy for boosting secondary-metabolite production in plants and that the transgenic expression of MtTPS10 enhances potato resistance to P. infestans.
Publications
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Botanik-Tagung, 15.-19.09.2024, Halle, Germany, Selected oral presentation: “Dissecting gene metabolite relationship in the Medicago truncatula terpenome after Aphanomyces euteiches infection”
Esther A. Harding
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International Plant Immunity Conference (IPIS 2024) 26.-28.08.2024, Goettingen, Germany, Poster presentation: “Root terpenoids, the hidden part of plant defense in the case of Medicago truncatula and Aphanomyces euteiches”
Esther A. Harding
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IS-MPMI Congress, 13.-17.07.2025, Cologne, Germany, Poster presentation: “Dissecting gene metabolite relationship in the Medicago truncatula terpenome after Aphanomyces euteiches infection”
Esther A. Harding
