Enzymatic study on AtCCD4 and AtCCD7 and their potential to form acyclic regulatory metabolites

Abstract
The Arabidopsis carotenoid cleavage dioxygenase 4 (AtCCD4) is a negative regulator of the carotenoid content of seeds and has recently been suggested as a candidate for the generation of retrograde signals that are thought to derive from the cleavage of poly-cis-configured carotene desaturation intermediates. In this work, we investigated the activity of AtCCD4 in vitro and used dynamic modeling to determine its substrate preference. Our results document strict regional specificity for cleavage at the C9–C10 double bond in carotenoids and apocarotenoids, with preference for carotenoid substrates and an obstructing effect on hydroxyl functions, and demonstrate the specificity for all-trans-configured carotenes and xanthophylls. AtCCD4 cleaved substrates with at least one ionone ring and did not convert acyclic carotene desaturation intermediates, independent of their isomeric states. These results do not support a direct involvement of AtCCD4 in generating the supposed regulatory metabolites. In contrast, the strigolactone biosynthetic enzyme AtCCD7 converted 9-cis-configured acyclic carotenes, such as 9-cis-ζ-carotene, 9'-cis-neurosporene, and 9-cis-lycopene, yielding 9-cis-configured products and indicating that AtCCD7, rather than AtCCD4, is the candidate for forming acyclic retrograde signals.

Citation
Bruno M, Koschmieder J, Wuest F, Schaub P, Fehling-Kaschek M, et al. (2016) Enzymatic study on AtCCD4 and AtCCD7 and their potential to form acyclic regulatory metabolites. Journal of Experimental Botany 67: 5993–6005. Available: http://dx.doi.org/10.1093/jxb/erw356.

Acknowledgements
This work was supported by the European Union (METAPRO; FP7 KBBE-2009-3-1-01) and the King Abdullah University of Science and Technology (KAUST).

Publisher
Oxford University Press (OUP)

Journal
Journal of Experimental Botany

DOI
10.1093/jxb/erw356

Additional Links
http://dx.doi.org/10.1093/jxb/erw356

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