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Functions of the plant CCD gene family Principal Investigators: |
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CCD Gene Family
Apocarotenoids are a diverse set of plant secondary metabolites derived from carotenoid breakdown. They have significant roles as developmental and environmental response signals. They also make important contributions to flavor and nutritional quality of foods. A critical advance in elucidating apocarotenoid synthesis occurred when the first gene encoding a carotenoid dioxygenase, maize Vp14, was cloned. Vp14 encodes the limiting enzyme in abscisic acid synthesis, 9-cis-epoxycarotenoid dioxygenase (NCED). Arabidopsis contains nine members of a gene family encoding enzymes related to NCED, referred to hereafter as CCDs (Carotenoid Cleavage Dioxgenase). Five family members are directly involved in abscisic acid synthesis while the other family members metabolize a range of carotenoids to multiple volatile and non-volatile apocarotenoids. One such enzyme, CCD1, cleaves multiple carotenoid substrates at different positions than NCED, indicating variation within the family both in carotenoid substrates and position of cleavage. We are establishing the functions of all Arabidopsis CCD enzymes. We have identified knock-out mutants in every CCD gene. Using bacterial expression and in vitro assays, the substrate specificities and products of each member of the CCD enzyme family is being determined. CCD1 cleaves a wide range of carotenoids at both the 5,6 and 9,10 double bonds, giving rise to a multitude of apocarotenoid products. Mutants have also been examined for phenotypic alterations. Knock-outs in CCD7 and CCD8 have a significant phenotype; each mutant has greatly reduced apical dominance. Grafting experiments indicate that these two enzymes act together to produce a novel apocarotenoid plant hormone that suppresses growth of lateral branches. Work to identify this new class of plant hormone is in progress.
The CCD Gene Family of Arabidopsis
| Gene | Accession | Chromosome | Gene ID | Function |
| AtCCD1 | AJ005813 | 3 | At3g63520 | 9,10-carotenoid-cleaving dioxygenase |
| AtNCED2 | AL021710 | 4 | At4g18350 | 11,12-cis-epoxycarotenoid dioxygenase |
| AtNCED3 | AB028617 | 3 | At3g14440 | 11,12-cis-epoxycarotenoid dioxygenase |
| AtCCD4 | AL021687 | 4 | At4g19170 | unknown |
| AtNCED5 | AC074176 | 1 | At1g30100 | 11,12-cis-epoxycarotenoid dioxygenase |
| AtCCD6 | AB028621 | 3 | At3g24220 | 11,12-cis-epoxycarotenoid dioxygenase |
| AtCCD7 | AC007659 | 2 | At2g44990 | 9,10-carotenoid-cleaving dioxygenase |
| AtCCD8 | AL161582 | 4 | At4g32810 | unknown |
| AtNCED9 | AC013430 | 1 | At1g78390 | 11,12-cis-epoxycarotenoid dioxygenase |
Click on accession number for link to NCBI entry
Phenotypes of ccd7 and ccd8 T-DNA knock-outs.
Both lines have shorter leaves and petioles. At the onset of flowering, all of the lateral shoots are simultaneously released from apical dominance.