Abstract

Artichoke has beneficial effects on human health, since it possesses anticarcinogenic, anti-HIV, antioxidative, cholesterol-lowering, bile expelling, hepatoprotective, and diuretic properties. These nutraceutical qualities are mainly due to polyphenolic compounds, particularly mono- and dicaffeoylquinic acids (e.g. chlorogenic acid, cynarin), caffeic acid and flavonoids (e.g. luteolin-7-O-glucoside, naringerin), with chlorogenic acid (CGA) being the most abundant. The content of polyphenol compounds, especially chlorogenic acid and cynarin, was measured in various tissues (leaves, bracts and receptacles) and physiological stages of artichoke plants, and in different artichoke genotypes belonging to the CNR-IGV Cynara world collection. A variation among tissues and genotypes was observed, and these variations were quite reproducible among years.On the same tissues, transcript levels of key genes for the synthesis of chlorogenic acid were measured by means of real time PCR. In particular, hqt genes, coding for HQT enzymes (acyltransferases of the BAHD family), have been shown to play a fundamental role in the synthesis of CGA in some plant species. Recently, hqt1 and hqt2 genes, possessing two exons and one intron each, have been isolated from artichoke, starting from Asteraceae EST sequences. Coding sequences were heterologously expressed in E. coli and the crude extract was used for enzyme chatracterization and substrate specificity. Both HQT1 and HQT2 were able to synthesize CGA in vitro and showed a remarkable preference towards quinate over shikimate, which distinguishes HQT enzyme class from HCT class (preferring shikimate). Based on the available crystallized structures of two BAHD enzymes, modeling and docking analyses were used to assume structural models for our HQT enzymes and to predict their potential binding sites.The content of CGA in the various tissues and genotypes analysed was more directly correlated with hqt1 expression levels. Moreover, transient and stable expression of HQT1 in Nicotiana benthamiana and in N. tabacum respectively, produced an increase in the content of CGA and cynarin, a derivative of CGA. Our findings indicate that both hqt1 and hqt2 are involved in the synthesis of CGA, but possibly at different steps of the metabolic pathway, and according to the plant exigencies. Moreover, the synthesis of cynarin (which is still unclear) might take place starting from CGA.

Autore Pugliese

• De Lisi Antonino , Blanco Emanuela , Sonnante Gabriella

Tutti gli autori

• Sonnante G.; Blanco E.; Negro D.; De Lisi A.; D'Amore R.; Pierri C.L.; De Palma M.; Tucci M.; Martin C.

Titolo volume/Rivista

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Anno di pubblicazione

2010

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Settori ERC

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