Caracterização e perfil de expressão de famílias gênicas envolvidas no metabolismo do ascorbato em pimenteira (Capsicum annuum L.)

Abstract

Ascorbate (ASC, vitamin C) is an antioxidant and enzyme cofactor essential for animals and plants. However, it is not synthesized by humans and its acquisition is primarily obtained from vegetables. The antioxidant action of ASC in plants reduces the excess of reactive oxygen species (ROS) generated under normal physiological conditions and especially in face of environmental stresses, through non-enzymatical and enzymatical responses involving the ascorbate-glutathione (ASC-GSH) cycle. Capsicum annuum L. includes several hot and bell peppers cultivars, which are widely recognized and consumed fruits due its high ASC content. However, the regulatory mechanisms involved in the metabolism of this micronutrient are still poorly understood in this species. Thus, this study, divided into three chapters, aims to advance on understanding of ASC metabolism in C. annuum. The first chapter presents a literature review about the production and effects of ROS, the antioxidant plant defense mechanisms, as well as the role and metabolism of ASC. The next two chapters examine the expression of the genes encoding to its biosynthesis (chapter 2) and the ASC-GSH cycle (chapter 3). In silico analyses were performed by collecting genomic data and nine RNA-Seq bioprojects representatives of fruit development, plant exposure to biotic and abiotic stresses, and phytohormones. A total of 21 genes encoding enzymes of the four proposed ascorbate biosynthesis pathways in pepper were identified. The expression data confirmed the major role of the L-galactose pathway in the different conditions analyzed, while genes from alternative pathways seem to play a supporting role under specific situations of stress and exposure to phytohormones. The members GGP2, GME1 and 2, and GalLDH emerged as promising regulatory targets. In relation to the ASC-GSH cycle, 14 genes were identified to encode isoenzymes acting in different subcellular compartments. The expression profile showed that APX3 and 5, from the oxidation pathway, were the most highly expressed genes in the different conditions analyzed, followed by APX2 and 6 in ripe red fruits and APX4 under abiotic stress and phytohormone treatments. Regarding the recycling pathway, MDHAR3, DHAR2 and GR2 members were more responsive under the different stress conditions analyzed. In conclusion, these results provide a better understanding on the transcriptional regulation of ASC metabolism in C. annuum and trace a path for future investigations aiming at the biofortification of crops with low ASC content, thus promoting increased nutritional value and tolerance to environmental stresses.