Abstract
Down-regulation of the potato carotenoid cleavage dioxygenase 4 (StCCD4) transcript level led to tubers with altered morphology and sprouting activity, which also accumulated higher levels of violaxanthin and lutein leading to elevated carotenoid amounts. This phenotype indicates a role of this enzyme in tuber development, which may be exerted by a cleavage product. In this work, we investigated the enzymatic activity of StCCD4, by expressing the corresponding cDNA in carotenoid accumulating Escherichia coli strains and by performing in vitro assays with heterologously expressed enzyme. StCCD4 catalyzed the cleavage of all-trans-beta-carotene at the C9'-C10' double bond, leading to beta-ionone and all-trans-beta-apo-10'-carotenal, both in vivo and in vitro. The enzyme also cleaved beta,beta-cryptoxanthin, zeaxanthin and lutein either at the C9'-C10' or the C9-C10 double bond in vitro. In contrast, we did not observe any conversion of violaxanthin and only traces of activity with 9-cis-beta-carotene, which led to 9-cis-beta-apo-10'-carotenal. Our data indicate that all-trans-beta-carotene is the likely substrate of StCCD4 in planta, and that this carotene may be precursor of an unknown compound involved in tuber development. (C) 2015 Elsevier Inc. All rights reserved.