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 �?-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.

Metabolic engineering of astaxanthin�?�rich maize and its use in the
production of biofortified eggs - Liu - 2021 - Plant Biotechnology
Journal - Wiley Online Library
[onlinelibrary.wiley.com]