4-ketocarotenoids in flower petals
The formation of a carotenoid compound containing a 4-keto-β-ionene ring such as astaxanthin or canthaxanthin in flowers, and particularly in the corolla and reproductive parts of a flower of a higher plant whose flowers produce a carotenoid compound containing a β-ionene ring such as β-carotene or zeaxanthin, but otherwise do not produce astaxanthin or canthaxanthin is disclosed. One or more genes controlled by a promoter are inserted (transformed) into a higher plant. The inserted gene encodes a chimeric enzyme including (a) a carotenoid-forming enzyme that is at least a ketolase. That gene is operatively linked to (b) a plastid-directed transit peptide. Some higher plants to be transformed produce at least zeaxanthin or β-carotene in their flowers prior to transformation, whereas other plants produce little if any colored carotenoid pigments prior to transformation and are transformed with a cassette of carotenoids-forming genes. Methods of transformation and use of the transformed plants are described.
1. A transgenic Tagetes erecta marigold plant or a regenerable portion thereof whose genome contains a transgene that encodes a chimeric ketolase enzyme polypeptide having two portions, (i) an N-terminal first portion comprising a plastid transit peptide portion fused to (ii) a second ketolase enzyme portion that converts a carotenoid β-ionene ring into a 4-keto-β-ionene ring, said transgene being operatively linked to a promoter that controls expression of said transgene, wherein the flower petals of said transgenic plant accumulate a carotenoid compound having a 4-keto-β-ionene ring, and wherein the flower petals of a host Tagetes erecta marigold that is not transformed with said chimeric ketolase, produce a carotenoid compound that contains a β-ionene ring having an unsubstituted 4-position and contains lutein that contains an β-ionene ring; and wherein said carotenoid compound produced in the petals of said host marigold contains a β-ionene ring having an unsubstituted 4-position that is one or both of β-carotene and zeaxanthin, and the ratio of the amount of β-carotene to the sum of the amounts of β-carotene and lutein present in said host flower petals is greater than about 1:10 or the ratio of the amount of zeaxanthin to the sum of the amounts of zeaxanthin and lutein present in said host flower petals is greater than about 1:10.
2. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 1 wherein said carotenoid compound having a 4-keto-β-ionene ring is a 4,4′-diketo-β-ionene ring carotenoid compound.
3. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 1 wherein said 4,4′-diketo-β-ionene ring carotenoid compound is canthaxanthin.
4. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 1 wherein said 4,4′-diketo-β-ionene ring carotenoid compound is astaxanthin.
5. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 1 wherein said plastid transit peptide portion is the RUBISCO transit peptide.
6. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 1 whose genome includes a second transgene that encodes a second chimeric polypeptide that contains (i) an N-terminal plastid transit peptide fused to (ii) a hydroxylase enzyme that converts a carotenoid β-ionene ring compound into a carotenoid 3-hydroxy-β-ionene ring compound, and said second transgene is operatively linked to a promoter that controls expression of said second transgene.
7. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 6 wherein said carotenoid compound having a 3-hydroxyl-β-ionene ring is a 3,3′-dihydroxy-β-ionene ring carotenoid compound.
8. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 7 wherein said 3,3′-dihydroxy-β-ionene ring carotenoid compound is zeaxanthin.
9. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 6 wherein said plastid transit peptide portion is the RUBISCO transit peptide.
10. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 1 wherein said ketolase enzyme portion that converts a carotenoid β-ionene ring into a carotenoid 4keto-β-ionene ring is a β-carotene-4oxygenase that is encoded by a gene present in one or more organisms selected from the group consisting of Adonis aestivalis, Agrobacterium aurantiacum, Alcaligenes sp., Bradyrhizobium sp., Brevundimonas aurantiaca, Haematococcus pluvialis, Nostoc sp., Paracoccus marcusii, Xanthophyllomyces dendrorhous, Synechocystis sp., Therrnosynechococcus elongates , and Trichodesmium erythraeum.
11. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 1 wherein said ketolase enzyme portion that converts a carotenoid 62 -ionene ring into a carotenoid 4-keto-β-ionene ring is encoded by the crtW gene of Agrobacterium aurantiacum.
12. The plant according to claim 1 wherein said ketolase enzyme portion that converts a carotenoid β-ionene ring into a carotenoid 4-keto-β-ionene ring is encoded by one or both of the AdK1 gene and AdK6 gene of Adonis aestivalis.
13. The plant according to claim 1 wherein said ketolase enzyme portion that converts a carotenoid β-ionene ring into a carotenoid 4-keto-β-ionene ring is encoded by the crtW gene of Alcaligenes sp.PC-1.
14. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 7 wherein said hydroxylase enzyme portion that converts a carotenoid β-ionene ring into a carotenoid 3-hydroxy-β-ionene ring is encoded by one or both of the crtZ genes of Erwinia uredovora and Erwinia herbicola.
15. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 1 wherein said promoter that controls expression of said transgene is a flower petal-preferred promoter.
16. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 1 wherein the carotenoid compound that contains a β-ionene ring having an unsubstituted 4-position produced in the flower petals of a plant of the same type that is not transformed with said chimeric ketolase is one or both of β-carotene and zeaxanthin.
17. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 16 wherein said plant of the same type that is not transformed with said chimeric ketolase is transformed with one or more DNA segments that encode one or more carotenoid-forming enzymes other than a ketolase.
18. The Tagetes erecta marigold plant or a regenerable portion thereof according to claim 1 that further includes one or more further transgenes selected from the group consisting of the (a) crtE, crtB, crtI, crtY and crtZ genes of Erwinia uredovora or (b) GGPP synthase, phytoene synthase, phytoene dehydrogenase(4H), lycopene cyclase, and β-carotene hydroxylase genes of Erwinia herbicola , wherein each of said further transgenes (i) is operatively linked to a promoter that directs flower petal-preferred expression of said transgene, and (ii) expresses a chimeric polypeptide enzyme that contains an N-terminal plastid transit peptide portion.