Maximizing astaxanthin production in engineered tobacco by integrating metabolomics-directed cultivation improvement and optimized raw-material processing

Tobacco is an excellent chassis for metabolic engineered biosynthesis of astaxanthin, a high-value carotenoid, yet efficient cultivation and processing methods remain to be established for enhancing its astaxanthin production. This work developed astaxanthin-producing tobacco plants utilizing the astaxanthin biosynthetic pathway from Adonis aestivalis and carried out metabolomics analyses to reveal the limits of astaxanthin-production efficiency in tobacco. The results showed that astaxanthin production altered the abundance of amino acids as well as a set of compounds involved in carbohydrate metabolism. The abundance of some downstream nitrogenous substances, such as nicotine, spermidine, uridine phosphate and guanosine phosphate, and organic acids in the tricarboxylic acid cycle were also changed in the astaxanthin-producing plants. These findings prompted us to determine the effects of additional nitrogen and carbon supply on astaxanthin production, which revealed that adding either or both of nitrogen and sucrose notably increased the biomass and astaxanthin production of tobacco. As high biomass plants, drying of the raw tobacco materials is required for further extraction. Efforts to optimize the processing method of raw-materials from astaxanthin-producing tobacco revealed that a direct vacuum-drying method could reduce the astaxanthin loss in tobacco leaves by ∼20 % in comparison with shade-drying or freeze-drying. This method also well retained the astaxanthin in tobacco stems and made them worthy of astaxanthin extraction. Integration of the high-nitrogen/sucrose cultivation and direct vacuum-drying methods essentially improved the whole-biomass utilization efficiency of astaxanthin-producing tobacco and resulted in ∼2 folds of astaxanthin yield, which may contribute greatly to cost effective astaxanthin production. • Alteration of primary metabolism was revealed in astaxanthin-producing tobacco. • Nitrogen and carbon supply increased biomass and astaxanthin production of tobacco. • Direct vacuum-drying reduced astaxanthin loss and increased the usability of stems. • Integrating optimized cultivation and direct vacuum-drying boosted astaxanthin yield.