Functional characterization of tomato PIF (Phytochrome Interacting Factors): role in fleshy fruit yield and nutritional quality

Tomato is a species of great economical and nutritional importance. During fruit ripening, chloroplasts are converted into chromoplasts, chlorophylls are degraded and secondary metabolites of nutraceutical importance, such as carotenoids and vitamin E (VTE), accumulate. Light plays a key role in the regulation of plastid activity and, therefore, of fruit nutritional quality. For instance, silencing of DE-ETIOLATED 1, a negative effector on light signaling, leads to increased chloroplast number and higher levels of chlorophyll, carotenoids and vitamin E in tomato fruits. On the other hand, light affects growth rates and flowering time in various species. In Arabidopsis thaliana, light-activated phytochromes (PHYs) induce the degradation of PHY- interacting factors (PIFs). PIFs as transcription factors acting as negative regulators of photomorphogenesis, part of a complex regulatory network that controls many developmental processes, from seed germination to senescence. AtPIFs directly regulate genes involved in plastid biogenesis and maintenance, chlorophyll breakdown, carotenogenesis, as well as pathways regulating growth and flowering. Therefore, PIFs emerge as potential targets of genetic manipulation towards improving fruit yield and quality. In this context, this work aimed to functionally characterize tomato PIFs. In Chapter I, SlPIFs were identified, and their diversity, evolutionary history and expression profile were studied. In Chapter II, the impacts of light on vitamin E biosynthesis and the role of SlPIFs as regulators of this process were investigated. In Chapter III, the effects of SlPIF4 constitutive silencing were evaluated regarding mainly fruit production and nutritional quality. Overall, this work brings new information that help understanding the role of SlPIFs in the regulation of important developmental and metabolic process, that ultimately affect agronomic and nutraceutical characteristic of the tomato fruit (AU)