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Mecanismes fisiològics del parasitisme: regulació hormonal i antioxidant en la interacció planta holoparàsita-hoste
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[cat] El parasitisme és una estratègia altament exitosa que ha evolucionat de manera convergent en tots els regnes biològics. En el regne vegetal, les plantes paràsites constitueixen un grup funcional molt especialitzat i encara poc conegut, capaç d’establir connexions vasculars amb plantes hoste per obtenir recursos essencials com aigua, minerals i carbohidrats. Les plantes holoparàsites, en concret, han experimentat una reducció evolutiva en la capacitat fotosintètica, esdevenint totalment dependents de l’hoste. Aquesta dependència dona lloc a una estreta interacció que requereix una regulació fisiològica complexa i coordinada entre l’hoste i la paràsita. Mentre la planta holoparàsita desplega mecanismes per infestar l’hoste i completar el seu cicle biològic, l’hoste modula la seva resposta defensiva per preservar el seu propi creixement i funcionalitat davant del parasitisme. Aquesta tesi explora la regulació hormonal i antioxidant en la interacció planta holoparàsita-hoste, utilitzant com a models un sistema agrícola d’interès econòmic i un sistema ecològic especialment rellevant en el clima Mediterrani. En el model agrícola, el parasitisme de Cuscuta campestris va accelerar el desenvolupament fenològic i va reduir dràsticament el rendiment del cultiu de llentia (Lens culinaris), superant els efectes provocats per un estrès hídric sever i sense que l’aplicació d’un compost bioestimulant pogués mitigar-ne les conseqüències. Aquesta interacció va anar acompanyada d’una acumulació simultània de jasmonoil-isoleucina (JA-Ile) i vitamina E, establint-se una relació sinèrgica que va modular la resposta defensiva i va induir una senescència prematura com a estratègia d’escapament davant el parasitisme en L. culinaris. Paral·lelament, aquesta mateixa interacció entre regulació hormonal i defensa antioxidant va ser clau en el desenvolupament de C. campestris, on la JA-Ile i la vitamina E van actuar, primer, durant l’estadi prehaustorial i, posteriorment, en l’haustori ja format, contribuint així en l’èxit del parasitisme i protegint la planta de l’estrès oxidatiu. Mitjançant un estudi sobre el rol de la vitamina E en la fotoprotecció durant la pèrdua progressiva de la capacitat fotosintètica associada a l’evolució del parasitisme en plantes, es va revelar la seva estreta associació amb les clorofil·les i el fotosistema II (PSII). A més, es va evidenciar la seva funció antioxidant i fotoprotectora en cloroplasts vestigials de C. campestris. Paral·lelament, es va estudiar el rol de la vitamina E en la defensa de l’hoste davant el parasitisme en un model d’interès ecològic. En concret, el romaní (Salvia rosmarinus) va augmentar la síntesi de tocoferols i va mostrar un increment en la ràtio ascorbat oxidat (DHA)/ascorbat total com a resposta a la interacció entre el parasitisme d’Orobanche latisquama i l’estrès hídric, suggerint així un mecanisme per mitigar l’efecte combinat d’aquests estressos. En conjunt, aquesta tesi posa de manifest la complexitat fisiològica i adaptativa de les interaccions planta holoparàsita-hoste, destacant el paper central de la regulació hormonal i la defensa antioxidant en la defensa de l’hoste i l’èxit de la paràsita. Els resultats obtinguts proporcionen noves perspectives per comprendre els mecanismes subjacents que determinen l’èxit del parasitisme i les respostes defensives de l’hoste, amb implicacions tant per a la gestió sostenible dels cultius com per a la comprensió de les dinàmiques ecològiques en sistemes naturals.
[eng] Parasitism represents a highly successful life strategy that has evolved convergently across all kingdoms of life. In the plant kingdom, parasitic plants constitute a highly specialized yet relatively understudied functional group capable of establishing vascular connections with host plants to obtain essential resources such as water, minerals, and carbohydrates. Holoparasitic plants, in particular, have undergone an evolutionary reduction in photosynthetic capacity, becoming completely dependent on their hosts. This dependency results in a close interaction that requires a complex and coordinated physiological regulation between the host and the parasite. While the holoparasitic plant deploys mechanisms to successfully establish itself on the host and complete its life cycle, the host modulates its defensive response to preserve its growth and functionality in the face of parasitism. This thesis explores the hormonal and antioxidant regulation within the holoparasite- host interaction, using an economically relevant agricultural system and an ecologically significant system in the Mediterranean climate as models. In the agricultural model, parasitism by Cuscuta campestris accelerated phenological development and drastically reduced the yield of lentil plants (Lens culinaris), surpassing the effects caused by severe water stress without mitigation from the application of a biostimulant compound. This interaction was accompanied by simultaneous accumulation of jasmonoyl-isoleucine (JA-Ile) and vitamin E, establishing a synergistic relationship that modulated the defensive response and induced premature senescence as an escape strategy from parasitism in L. culinaris. In parallel, this same interaction between hormonal regulation and antioxidant defense was essential for the development of C. campestris, where JA-Ile and vitamin E acted first during the prehaustorial stage and later in the fully formed haustorium, thereby contributing to successful parasitism and protecting the plant from oxidative stress. Through a study on the role of vitamin E in photoprotection during the progressive loss of photosynthetic capacity associated with the evolution of parasitism in plants, its close association with chlorophylls and photosystem II (PSII) was revealed. Additionally, its antioxidant and photoprotective functions were demonstrated in the vestigial chloroplasts of C. campestris. Moreover, the role of vitamin E in host defense against parasitism was further studied using an ecologically relevant model. Specifically, rosemary (Salvia rosmarinus) increased tocopherol synthesis and exhibited an enhanced oxidized ascorbate (DHA)/total ascorbate ratio in response to the interaction between Orobanche latisquama parasitism and water stress, suggesting a mechanism to mitigate the combined effects of these stresses. Overall, this thesis highlights the physiological and adaptive complexity of holoparasitic plant- host interactions, emphasizing the central role of hormonal regulation and antioxidant defense in host protection and parasitic success. The findings obtained provide new insights into the underlying mechanisms that determine parasitism success and host defensive responses, with implications for both the sustainable management of crops and the understanding of ecological dynamics in natural system
[eng] Parasitism represents a highly successful life strategy that has evolved convergently across all kingdoms of life. In the plant kingdom, parasitic plants constitute a highly specialized yet relatively understudied functional group capable of establishing vascular connections with host plants to obtain essential resources such as water, minerals, and carbohydrates. Holoparasitic plants, in particular, have undergone an evolutionary reduction in photosynthetic capacity, becoming completely dependent on their hosts. This dependency results in a close interaction that requires a complex and coordinated physiological regulation between the host and the parasite. While the holoparasitic plant deploys mechanisms to successfully establish itself on the host and complete its life cycle, the host modulates its defensive response to preserve its growth and functionality in the face of parasitism. This thesis explores the hormonal and antioxidant regulation within the holoparasite- host interaction, using an economically relevant agricultural system and an ecologically significant system in the Mediterranean climate as models. In the agricultural model, parasitism by Cuscuta campestris accelerated phenological development and drastically reduced the yield of lentil plants (Lens culinaris), surpassing the effects caused by severe water stress without mitigation from the application of a biostimulant compound. This interaction was accompanied by simultaneous accumulation of jasmonoyl-isoleucine (JA-Ile) and vitamin E, establishing a synergistic relationship that modulated the defensive response and induced premature senescence as an escape strategy from parasitism in L. culinaris. In parallel, this same interaction between hormonal regulation and antioxidant defense was essential for the development of C. campestris, where JA-Ile and vitamin E acted first during the prehaustorial stage and later in the fully formed haustorium, thereby contributing to successful parasitism and protecting the plant from oxidative stress. Through a study on the role of vitamin E in photoprotection during the progressive loss of photosynthetic capacity associated with the evolution of parasitism in plants, its close association with chlorophylls and photosystem II (PSII) was revealed. Additionally, its antioxidant and photoprotective functions were demonstrated in the vestigial chloroplasts of C. campestris. Moreover, the role of vitamin E in host defense against parasitism was further studied using an ecologically relevant model. Specifically, rosemary (Salvia rosmarinus) increased tocopherol synthesis and exhibited an enhanced oxidized ascorbate (DHA)/total ascorbate ratio in response to the interaction between Orobanche latisquama parasitism and water stress, suggesting a mechanism to mitigate the combined effects of these stresses. Overall, this thesis highlights the physiological and adaptive complexity of holoparasitic plant- host interactions, emphasizing the central role of hormonal regulation and antioxidant defense in host protection and parasitic success. The findings obtained provide new insights into the underlying mechanisms that determine parasitism success and host defensive responses, with implications for both the sustainable management of crops and the understanding of ecological dynamics in natural system
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JENÉ VINUESA, Laia. Mecanismes fisiològics del parasitisme: regulació hormonal i antioxidant en la interacció planta holoparàsita-hoste. [consulta: 27 de febrer de 2026]. [Disponible a: https://hdl.handle.net/2445/226840]