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Glucosylation of the saffron apocarotenoid crocetin by a glucosyltransferase isolated from Crocus sativus stigmas

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Saffron, the dry stigma of Crocus sativus L., is considered to be the world’s most expensive spice. Three major apocarotenoids—crocin, crocetin and picrocrocin—are responsible for the colour and bitter taste of saffron. The final step in the biosynthesis of the 20-carbon esterified carotenoid crocin is the transformation of the insoluble crocetin into a soluble and stable storage form by glucosylation. These glucosylation reactions are catalysed by glucosyltransferases (GTases) that play a crucial role in natural-product biosynthesis. Using degenerate primers designed to match the plant secondary product GTase (PSPG) box we cloned two cDNAs, UGTCs2 and UGTCs3, from C. sativus stigmas that encode putative polypeptides of 460 and 475 amino acids, respectively. These genes were expressed differentially in saffron tissues. UGTCs2 was mainly expressed in fully developed stigmas, whereas UGTCs3 was mainly expressed in stamens. The UGTCs2 transcript was not detected in the stigma tissue of a Crocus species that does not synthesize crocin, while UGTCs3 and other structural genes for carotenoid biosynthesis were expressed in the stigma of all tested Crocus species. To identify the biochemical function of UGTCs2, the isolated cDNA was expressed in Escherichia coli cells. The recombinant protein UGTCs2 had glucosylation activity against crocetin, crocetin β-d-glucosyl ester and crocetin β-d-gentibiosyl ester. These results might suggest that the isolated clone UGTCs2 codes for a saffron crocetin GTase.

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Abscisic acid


β-Carotene hydroxylase


Indole acetic acid

GA 3 :

Gibberellic acid

GTase :


JA :

Jasmonic acid


Phytoene synthase


Rapid amplification of cDNA ends

SA :

Salicylic acid


UDP-glucosyl transferase


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We gratefully acknowledge the contribution of R. Castillo in the collection and preparation of some RNA samples. We thank Drs. A. Gómez and D. Lunt (Hull University, UK) for critical reading of the manuscript and corrections; the Biochemistry Department of Valencia University (Spain) for radiation laboratory facilities; and Drs. N. Kayali (Universidad Complutense de Madrid, Spain) and O. Jauregui (Barcelona University, Spain) for the mass spectra facilities and analysis. This research was supported by Consejería de Ciencia y Tecnología de la JCCM grant No. PAI-02-026 and MCyT grant BIO2003-05259.

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Correspondence to Lourdes Gómez-Gómez.

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Moraga, A.R., Nohales, P.F., Pérez, J.A.F. et al. Glucosylation of the saffron apocarotenoid crocetin by a glucosyltransferase isolated from Crocus sativus stigmas. Planta 219, 955–966 (2004).

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