PMID:19120446

Citation	Ilg, A, Beyer, P and Al-Babili, S (2009) Characterization of the rice carotenoid cleavage dioxygenase 1 reveals a novel route for geranial biosynthesis. FEBS J. 276:736-47
Abstract	Carotenoid cleavage products--apocarotenoids--include biologically active compounds, such as hormones, pigments and volatiles. Their biosynthesis is initiated by the oxidative cleavage of C-C double bonds in carotenoid backbones, leading to aldehydes and/or ketones. This step is catalyzed by carotenoid oxygenases, which constitute an ubiquitous enzyme family, including the group of plant carotenoid cleavage dioxygenases 1 (CCD1s), which mediates the formation of volatile C(13) ketones, such as beta-ionone, by cleaving the C9-C10 and C9'-C10' double bonds of cyclic and acyclic carotenoids. Recently, it was reported that plant CCD1s also act on the C5-C6/C5'-C6' double bonds of acyclic carotenes, leading to the volatile C(8) ketone 6-methyl-5-hepten-2-one. Using in vitro and in vivo assays, we show here that rice CCD1 converts lycopene into the three different volatiles, pseudoionone, 6-methyl-5-hepten-2-one, and geranial (C(10)), suggesting that the C7-C8/C7'-C8' double bonds of acyclic carotenoid ends constitute a novel cleavage site for the CCD1 plant subfamily. The results were confirmed by HPLC, LC-MS and GC-MS analyses, and further substantiated by in vitro incubations with the monocyclic carotenoid 3-OH-gamma-carotene and with linear synthetic substrates. Bicyclic carotenoids were cleaved, as reported for other plant CCD1s, at the C9-C10 and C9'-C10' double bonds. Our study reveals a novel source for the widely occurring plant volatile geranial, which is the cleavage of noncyclic ends of carotenoids.
Links	PubMed Online version:10.1111/j.1742-4658.2008.06820.x
Keywords	Biocatalysis; Carotenoids/chemistry; Carotenoids/metabolism; Dioxygenases/metabolism; Mass Spectrometry; Molecular Structure; Oryza sativa/enzymology; Oryza sativa/metabolism; Substrate Specificity; Terpenes/chemistry; Terpenes/metabolism
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
ORYSJ:Q8LQQ2		GO:0010437: 9,10 (9', 10')-carotenoid-cleaving dioxygenase activity	ECO:0000314:		F		Fig 5: OsCCD1 exhibited by far the highest preference for the C9-C10 double bond in vitro. As suggested by the predominance of the C(17) dialdehye (90% of the total dialdehyde products)	complete CACAO 4960

References

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