RESUMEN
Transgenic Solanum lycopersicum plants expressing an additional copy of the lycopene ß-cyclase gene (LCYB) from Nicotiana tabacum, under the control of the Arabidopsis polyubiquitin promoter (UBQ3), have been generated. Expression of LCYB was increased some 10-fold in ripening fruit compared to vegetative tissues. The ripe fruit showed an orange pigmentation, due to increased levels (up to 5-fold) of ß-carotene, with negligible changes to other carotenoids, including lycopene. Phenotypic changes in carotenoids were found in vegetative tissues, but levels of biosynthetically related isoprenoids such as tocopherols, ubiquinone and plastoquinone were barely altered. Transformants showed tolerance to the bleaching herbicide ß-cyclase inhibitor, 2-(4-chlorophenylthio) triethylamine. The phenotype was inherited for at least three generations.
Asunto(s)
Carotenoides/metabolismo , Frutas/metabolismo , Liasas Intramoleculares/metabolismo , Nicotiana/enzimología , Proteínas de Plantas/metabolismo , Solanum lycopersicum/metabolismo , beta Caroteno/metabolismo , Northern Blotting , Carotenoides/química , Etilaminas/farmacología , Frutas/genética , Regulación Enzimológica de la Expresión Génica , Regulación de la Expresión Génica de las Plantas , Resistencia a los Herbicidas/genética , Liasas Intramoleculares/genética , Licopeno , Solanum lycopersicum/genética , Ingeniería Metabólica/métodos , Estructura Molecular , Hojas de la Planta/genética , Hojas de la Planta/metabolismo , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente , Nicotiana/genética , beta Caroteno/químicaRESUMEN
Although higher plants synthesize carotenoids, they do not possess the ability to form ketocarotenoids. In order to generate higher plants capable of synthesizing combinations of ketolated and hydroxylated carotenoids the genes responsible for the carotene 4,4' oxygenase and 3,3' hydroxylase have been transformed into tomato and tobacco. The gene products were produced as a polyprotein. Subsequent cleavage of the polyprotein, targeting of the two enzymes to the plastid and enzyme activities have been shown for both gene products. Metabolite profiling has shown the formation of ketolated carotenoids from beta-carotene and its hydroxylated intermediates in tobacco and tomato leaf. In the nectary tissues of tobacco flowers a quantitative increase (10-fold) as well as compositional changes were evident, including the presence of astaxanthin, canthaxanthin and 4-ketozeaxanthin. Interestingly, in this tissue the newly formed carotenoids resided predominantly as esters. These data are discussed in terms of metabolic engineering of carotenoids and their sequestration in higher plant tissues.