José Tomás Matús, Chen Zhang

This thesis, directed by José Tomás Matus, explores the transcriptional regulation networks associated with the biosynthesis of terpenes, an important family of aromas, pigments or hormones present in plants that play fundamental roles in the relationship of these organisms with the environment. Part of the research results have been published in the journal Plant Cell. The thesis was defended on December 12, 2023.

Plants are a source of a great diversity of compounds that contribute to their interaction with the environment. These compounds vary between species and are the product of specialized (secondary) metabolic pathways derived from primary metabolism. Among them, the isoprenoid pathway is one of the main biosynthetic processes of specialized metabolism and gives rise to the production of aromas (for example, terpenoids or apocarotenoids), pigments (such as carotenoids) or hormones, among many other types of compounds. Terpene synthases (TPS), responsible for the synthesis of sesquiterpenes, monoterpenes and diterpenes, are present in most plants and their function and substrate specificity have been widely investigated. They contribute to the set of volatile organic compounds (VOCs) with various functions in animal attraction, herbivore repellence, antioxidant processes and even antipathogenic properties. Although the terpenoid pathway is fairly conserved among plants, the end products differ between species, and this may be the result of differences in both structural genetic composition and regulation of gene expression. In contrast to the extensive studies on their enzymatic activity, the transcriptional regulation of TPS genes has been less explored. However, a few families of transcription factors have been implicated as associated with the regulation of terpenoid biosynthesis, including members of the R2R3-MYB family. In this thesis, titled "Topology and evolution of gene regulatory networks modulating aroma synthesis in plants", the regulatory roles of a subgroup of 19 genes belonging to this family have been functionally characterized. Previous studies have shown that S19-MYBs are regulators of floral maturation, with the emission of VOCs being a particularly conserved event in the last stages of flower development. In particular, the ability of S19-MYBs to bind and regulate terpenoid biosynthesis genes has been explored, using grapevine (Vitis vinifera), tomato (Solanum lycopersicum) and Cannabis sativa as case studies. Furthermore, the degree of conservation of S19-MYBs in plants has been studied to unravel whether the regulation of TPS by S19-MYBs is only present in Angiosperms.

Chen Zhang carried out his doctoral research in the Transcriptional Orchestration of Metabolism group under the supervision of José Tomás Matus, Ramón y Cajal (UV) researcher at the Institute of Integrative Systems Biology I2SysBio (UV-CSIC). During the development of the project, Chen Zhang has enjoyed a contract from the China Scholarship Council (CSC) and has carried out a research stay at the University of Verona. The qualifying panel was made up of María Purificación Lisón Párraga (Universitat Politècnica de València), Sara Rosa Téllez (UV), and Vicente Arbona Mengual (Universitat Jaume I), who rated the thesis as outstanding.