Evaluation of transgenic tomato plants expressing an additional phytoene synthase in a fruit-specific manner

Abstract

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, ␤-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 T2 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.carotenoids ͉ metabolic engineering

A comprehensive review on the colorless carotenoids phytoene and phytofluene

“…In any case, the typical commited step of carotenoid biosynthesis is the condensation of two molecules of the C20 compound geranylgeranyl pyrophosphate (GGPP) to form (15Z)-phytoene, the major PT isomer in most carotenogenic organisms [18,19], as stated before. This reaction is catalyzed by the enzyme phytoene synthase (PS), which is a key regulatory enzyme in the pathway [24][25][26][27]. Phytoene is therefore the precursor of all carotenoids.…”

Combinatorial genetic transformation generates a library of metabolic phenotypes for the carotenoid pathway in maize

“…The overexpression of phytoene synthase has a potent effect on carotenoid levels in storage organs generally, e.g., resulting in a 1.9-fold increase in tomato fruits (26), a 50-fold increase in canola seeds (27), and an 8-fold increase in potato tubers (28). In our equivalent maize plants (Ph-1, overexpressing Zmpsy1), the total endosperm carotenoid levels were elevated 53-fold, but the expression of 2 sequential enzymes (ZmPSY1 and PaCRTI in Ph-3) resulted in a further tripling of the carotenoid levels.…”

Synthesis of carotenoids and regulation of the carotenoid biosynthesis pathway in response to high light stress in the unicellular microalga Chlamydomonas reinhardtii

“…However, in many cases, unexpected collateral effects, low functionality or silencing of the exogenous genes has reduced the productivity or viability of the new transgenic strains (Ye et al, 2000;Fraser et al, 2002;Paine et al, 2005;Diretto et al, 2007). Despite the physiological and economic importance of this metabolic route in microalgae, many regulatory aspects are not clear and several genes remain unidentified.…”