Phosphoenolpyruvate carboxylase (PEPC) plays a central role in the anaplerotic provision of carbon skeletons for amino acid biosynthesis in leaves of C3 plants. Furthermore, in both C4 and CAM plants photosynthetic isoforms are pivotal for the fixation of atmospheric CO2. Potato PEPC was mutated either by modifications of the N-terminal phosphorylation site or by an exchange of an internal cDNA segment for the homologous sequence of PEPC from the C4 plant Flaveria trinervia. Both modifications resulted in enzymes with lowered sensitivity to malate inhibition and an increased affinity for PEP. These effects were enhanced by a combination of both mutated sequences and pulse labelling with 14CO2 in vivo revealed clearly increased fixation into malate for this genotype. Activity levels correlated well with protein levels of the mutated PEPC. Constitutive overexpression of PEPC carrying both N-terminal and internal modifications strongly diminished plant growth and tuber yield. Metabolite analysis showed that carbon flow was re-directed from soluble sugars and starch to organic acids (malate) and amino acids, which increased four-fold compared with the wild type. The effects on leaf metabolism indicate that the engineered enzyme provides an optimised starting point for the installation of a C4-like photosynthetic pathway in C3 plants.

Tocopherols, collectively known as vitamin E, are only synthesised in photosynthetic organisms. Tocopherol cyclase (TC) catalyses the formation of the chromanol headgroup of the various tocopherol isoforms. TCs from Arabidopsis and maize (Zea mays) were expressed in Escherichia coli and purified. Analysis of the enzymatic properties revealed similarities but also differences between the two enzymes. Overexpression of chimeric TC gene constructs in developing seeds of transgenic rapeseed plants enhanced and modified the relative abundance of individual tocochromanol species in the seed oil, indicating a regulatory function of the enzyme in prenyllipid metabolism.

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The erucoyl-CoA specific sn-1-acylglycerol-3-phosphate acyltransferase (LPAAT) of Limnanthes douglasii was functionally expressed in developing seeds of differing high-erucic acid rapeseed genotypes, namely resynthesized lines and cultivars. Lipid analysis revealed that seed oil of transgenic plants in contrast to that of control plants contained trierucoylglycerol as well as a molecular species with two erucoy1 groups and one eicosenoyl group. The proportion of trierucoylglycerol was distinctly higher in the seeds from transgenic resynthesized plants than in those from transgenic cultivars. In pooled seed oil fractions, up to 9% trierucoylglycerol (trierucin) was determined and the fatty acid composition at the sn-2 position was found to consist of more than 40% erucic acid. Since the pooled seeds were segregating for the presence of the L. douglasii gene, the analysis of single seeds gave even higher levels of up to 13% trierucin. Biosynthese von Trierucoylglycerol in transgener Rapssaat(Brassica napus L). Die erucoyl-CoA-spezifische sn-1-Acylglycerin-3-phosphat-Acyltransferase (LPAAT) aus Limnanthes douglasii wurde in den reifenden Samen verschiedener erucasaurereicher Rapssorten und Resyntheselinien funktional exprimiert. Wie Lipidanalysen zeigten, enthielt das Samenol transgener Pflanzen, im Unterschied zu den Kontrollen,Trierucin sowie eine molekulare Spezies mit zwei Erucasaure-und einem Eicosensaurerest. Im Vergleich der Sorten war bei den Resyntheselinien der Trierucinanteil in den Samen transgener Pflanzen deutlich hoher. In vereinigten Samenolfraktionen betrug der Trierucingehalt bis zu 9% und der Erucasauregehalt in der sn-2-Position mehr als 40%. Aufgrund der Segregation des L. douglasii-Gens konnten bei der Analyse einzelner Samen hohere Trierucingehalte von bis zu 13% gemessen werden.