Xiaoqing Liu, Xuhui Ma, Hao Wang, Suzhen Li, Wenzhu Yang, Ramdhan Dwi Nugroho, Lili Luo, Xiaojin Zhou, Chaohua Tang, Yunliu Fan, Qingyu Zhao, Junmin Zhang, Rumei Chen.

Plant Biotechnology Journal; 29 March 2021; https://doi.org/10.1111/pbi.13593

Summary

Production of the high-value carotenoid astaxanthin, which is widely used in food and feed due to its strong antioxidant activity and colour, is less efficient in cereals than in model plants. Here, we report a new strategy for expressing β-carotene ketolase and hydroxylase genes from algae, yeasts and flowering plants in the whole seed using a seed-specific bidirectional promoter. Engineered maize events were backcrossed to inbred maize lines with yellow endosperm to generate progenies that accumulate astaxanthin from 47.76 to 111.82 mg/kg DW in seeds, and the maximum level is approximately sixfold higher than those in previous reports (16.2–16.8 mg/kg DW) in cereals. A feeding trial with laying hens indicated that they could take up astaxanthin from the maize and accumulate it in egg yolks (12.10–14.15 mg/kg) without affecting egg production and quality, as observed using astaxanthin from Haematococcus pluvialis. Storage stability evaluation analysis showed that the optimal conditions for long-term storage of astaxanthin-rich maize are at 4 °C in the dark. This study shows that co-expressing of functional genes driven by seed-specific bidirectional promoter could dramatically boost astaxanthin biosynthesis in every parts of kernel including embryo, aleurone layer and starch endosperm other than previous reports in the starch endosperm only. And the staple crop maize could serve as a cost-effective plant factory for reliably producing astaxanthin.

See: https://onlinelibrary.wiley.com/doi/10.1111/pbi.13593

Figure 2: Development of astaxanthin-rich maize. (a) Schematic diagram of the constructs pBDEN-CP-BZ and pBDEN-CP-BZ-RNAi, functional genes and sense (lcy-e) and anti-sense (lcy-e′) fragments of ZmLCY-e directed by the seed-specific bidirectional promoter P_R5SGPA. (b–g) Engineered astaxanthin-rich maize seeds at different developmental stages; (b–d) seeds derived from pBDEN-CP-BZ; (e–g) seeds derived from pBDEN-CP-BZ-RNAi; (b, e) at 20 days after pollination (DAP); (c, f) at 30 DAP; (d, g) mature dry seeds. (h–l) High-performance liquid chromatography (HPLC) analysis of astaxanthin in dried astaxanthin-rich maize seeds; (h) a mixture of all-E, 9Z and 13Z astaxanthin standards; (i) the transgenic event LX68-1, derived from pBDEN-CP-BZ; (j) the transgenic event LX71-2, derived from pBDEN-CP-BZ-RNAi; (k) the yellow endosperm inbred line Z58 used as the recurrent parent; (l) quantitative analysis of isomers and total astaxanthin. all-E, all-trans geometric isomer; 9Z, cis-9 geometric isomer; 13Z, cis-13 geometric isomer. All data were derived from three technical repetitions.