Mechanisms of Apocarotenoid Metabolism and Signaling

• Applicant: Privatdozent Dr. Ralf Welsch
• Subject Area: Plant Biochemistry and Biophysics ; Plant Physiology
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 409147917

Carotenoids have a large array of functions throughout a plant’s life and are essential for animals including humans as their provitamin A function is required for vision and development. Once synthesized in plant tissues, carotenoids are unstable and converted enzymatically into plant hormones and scents and – due to their role as antioxidants - are non-enzymatically oxidized into various apocarotenoids. Concluded from high steady-state rates of carotenoid biosynthesis, their turnover and also the formation of apocarotenoids occur with similar high rates. While research on enzymes and mechanisms of carotenoid synthesis progressed impressively, knowledge on the processes involved in apocarotenoid metabolization is sparse. In order to identify corresponding mechanisms, we determined transcriptome changes in Arabidopsis roots in which apocarotenoid-metabolizing processes were induced through b-carotene overaccumulation. Induced differentially expressed genes were associated with carbonyl stress response required to detoxify highly reactive apocarotenoids. This was confirmed biochemically with one identified enzyme which detoxified specific apocarotenals into derivatives with reduced reactivity. Moreover, we observed carotenoid pathway-specific responses targeting to reduce the synthesis of b-carotene which indicates perception of b-carotene as the source for apocarotenoid/carbonyl overload. In this project we will continue characterizing novel apocarotenoid-metabolizing enzymes and identify corresponding metabolites and intracellular transport processes in plants. Moreover, we will identify pathway-specific molecules with signaling function capable in transmitting information of imbalanced b-carotene levels on gene expression changes. Finally, we found that continued oxidation of apocarotenoids generates glyoxal and methylglyoxal. Therefore, we will investigate a possible carotenoid-derived carbon remobilization into primary metabolic pathways. Our results will generate a template for analyses of corresponding processes in crops with largely different carotenoid stability and provide novel approaches to obtain enhanced carotenoid levels. Furthermore, the proposed carotenoid recycling process might significantly boost our understanding of the connection between anabolic and catabolic pathways in plastid metabolism.

• DFG Programme: Research Grants
• International Connection: Italy
• Cooperation Partner: Professor Dr. Giovanni Giuliano, Ph.D.
• Co-Investigator: Privatdozentin Shizue Matsubara, Ph.D.