Carotenoid Biosynthesis in Seed of Arabidopsis thaliana

Seed of Arabidopsis thaliana accumulate carotenoids during development. These are mainly β-carotene, violaxanthin and lutein. By overexpression of an endogenous phytoene synthase (psy) under control of the seed-specific napin (nap) promoter the carotenoid content was elevated, resulting in increased levels in mainly β-carotene, violaxanthin, lutein and α-carotene. Transgenic seeds were also found to contain increased levels of ABA and displayed a delay in germination. The levels of ABA had a good correlation to the varying increases in lutein and violaxanthin content in seeds from plants hemizygous for the nap:psy construct. Seeds from plants overexpressing a β-carotene ketolase (bkt) from the green algae Haematococcus pluvialis, also under control of the napin promoter contained small amounts of ketocarotenoids, mainly 4-keto-lutein. When plants carrying the nap:bkt construct were crossed to plants carrying nap:psy this resulted in seeds where the total ketocarotenoid content had increased up to 13-fold. In seeds of the aba1-3 mutant of Arabidopsis which is mutated in the zeaxanthin epoxididase (zep) zeaxanthin levels were increased up to 40-fold and in seed of plants overexpressing an endogenous β-carotene hydroxylase (bch) it was found that the violaxanthin content had increased up to 20-fold. In seed from plants transgenic for nap:bch, neoxanthin and ABA levels were also increased. Just as for plants transgenic for nap:psy these seeds displayed a delay in germination. When γ-tocopherol content was analysed it was found that in seeds of nap:psy and nap:bch transformants it was only half of that found in wild type. In the Arabidopsis mutant abscisic acid-insensitive 3-1 (abi3-1) that is mutated in a seed-specific transcription factor, the seeds were found to have increased levels of β-carotene, violaxanthin, lutein and γ-tocopherol.