Functional characterization of the Gentiana lutea zeaxanthin epoxidase (GlZEP) promoter in transgenic tomato plants
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The accumulation of carotenoids in plants depends critically on the spatiotemporal expression profiles of the genes encoding enzymes in the carotenogenic pathway. We cloned and characterized the Gentiana lutea zeaxanthin epoxidase (GlZEP) promoter to determine its role in the regulation of carotenogenesis, because the native gene is expressed at high levels in petals, which contain abundant chromoplasts. We transformed tomato (Solanum lycopersicum cv. Micro-Tom) plants with the gusA gene encoding the reporter enzyme b-glucuronidase (GUS) under the control of the GlZEP promoter, and investigated the reporter expression profile at the mRNA and protein levels. We detected high levels of gusA expression and GUS activity in chromoplastcontaining flowers and fruits, but minimal levels in immature fruits containing green chloroplasts, in sepals, leaves, stems and roots. GlZEP-gusA expression was strictly associated with fruit development and chromoplast differentiation, suggesting an evolutionarily-conserved link between ZEP and the differentiation of organelles that store carotenoid pigments. The impact of our results on current models for the regulation of carotenogenesis in plants is discussed.