ESCUELA DE DOCTORADO

 
Tesis Doctorales de la Universidad de Alcalá
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CHANGES IN METABOLIC PROFILE AND DEFENSE SYSTEMS IN LICHEN MICROALGAE WITH DIFFERENT DESICCATION TOLERANCE
Autor/aForgatti Hell, Aline
DepartamentoBiomedicina y Biotecnología
Director/aCasano Mazza, Leonardo Mario
Codirector/aDa Cruz Centeno, Danilo
Fecha de defensa14/09/2020
CalificaciónSobresaliente Cum Laude
ProgramaBiología Funcional y Biotecnología (RD 99/2011)
Mención internacionalSi
ResumenMost lichens and their photobionts are considered desiccation tolerant, however, the mechanisms involved in their incredible ability to survive the water loss and resume active metabolism are still poorly studied. It is believed that the desiccation tolerance (DT) of lichenized photobionts may be, at least partially, associated with constitutive and induced species-specific mechanisms of protection, related with the activation of the antioxidant system and the synthesis of protective molecules. Thus, the objective of this PhD Thesis was to analyze the composition, metabolic and defense system alterations of two species of lichenized microalgae, with different hydric behaviors: Trebouxia sp. (TR9) and Coccomyxa simplex (Csol) and relate them with the DT of each species. For this, analyzes of metabolic profile, antioxidant enzymes, characterization of polyols, and quantification of nitric oxide (NO) and transcripts levels of antioxidant and sugar alcohols-related genes were performed. Initially, microalgae cultures were subjected to a single cycle of desiccation-rehydration (D/R), under relative humidity (RH) of 25%-30%. Under these conditions, the relative water content and the water potential indicated that each specie present a DT strategy adjusted to the water regime of their natural habitat. The metabolic profile analysis indicated that TR9 constitutively accumulated higher amounts of polyols, while Csol induced the synthesis of these compounds, which seemed to play an important role in the DT of both species. In a second approach, DT was tested by subjecting the species to different RH conditions and consecutive D/R cycles. The results showed that the RH close to that of their natural habitats (RH 25% for TR9 and RH 60% for Csol) is crucial for maintaining the photosynthetic rates. Some key antioxidant enzyme activities and antioxidant genes (transcript levels) were induced by the subsequent D/R cycles in a species-specific way, probably due to the increase in the formation of reactive oxygen species (ROS). In addition, the analysis of the transcript levels related to the synthesis of myo-inositol and raffinose also demonstrated, in general, an induction during the consecutive D/R cycles, especially in Csol. Correlation analyzes also suggest that NO can act as signaling factor, assisting to modulate metabolic pathways of polyols production. In conclusion, among the experimental evidences presented in this PhD Thesis, it is highlighted the species-specific induction of the antioxidant system and synthesis of polyols by exposition to cyclic desiccation, which strongly suggest a process of metabolic "priming" performed by lichenized microalgae to cope with the oxidative and osmotic stress during the sudden changes in water content to which they are normally subjected