Evaluation of transgenic tomato plants expressing an additional phytoene synthase in a fruit-specific manner.
Phytoene synthase from the bacterium Erwinia uredovora (crtB) has been overexpressed in tomato (Lycopersicon esculentum Mill. cv. Ailsa Craig). Fruit-specific expression was achieved by using the tomato polygalacturonase promoter, and the CRTB protein was targeted to the chromoplast by the tomato phytoene synthase-1 transit sequence. Total fruit carotenoids of primary transformants (T(0)) were 2-4-fold higher than the controls, whereas phytoene, lycopene, beta-carotene, and lutein levels were increased 2.4-, 1.8-, and 2.2-fold, respectively. The biosynthetically related isoprenoids, tocopherols plastoquinone and ubiquinone, were unaffected by changes in carotenoid levels. The progeny (T(1) and T(2) generations) inherited both the transgene and phenotype. Determination of enzyme activity and Western blot analysis revealed that the CRTB protein was plastid-located and catalytically active, with 5-10-fold elevations in total phytoene synthase activity. Metabolic control analysis suggests that the presence of an additional phytoene synthase reduces the regulatory effect of this step over the carotenoid pathway. The activities of other enzymes in the pathway (isopentenyl diphosphate isomerase, geranylgeranyl diphosphate synthase, and incorporation of isopentenyl diphosphate into phytoene) were not significantly altered by the presence of the bacterial phytoene synthase.
Fraser
Paul D
PD
School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey TW20 OEX, United Kingdom.
Romer
Susanne
S
Shipton
Cathie A
CA
Mills
Philippa B
PB
Kiano
Joy W
JW
Misawa
Norihiko
N
Drake
Rachel G
RG
Schuch
Wolfgang
W
Bramley
Peter M
PM
D019883:Alkyl and Aryl Transferases / Q000235:genetics*; D002338:Carotenoids / Q000378:metabolism; D015870:Gene Expression; D005798:Genes, Bacterial; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D018551:Solanum lycopersicum / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism; D016973:Pectobacterium carotovorum / Q000201:enzymology / Q000235:genetics; D030821:Plants, Genetically Modified; D014018:Tissue Distribution
D002338:Carotenoids; D019883:Alkyl and Aryl Transferases; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase