Cloning and characterization of cystathionine gamma-synthase from Solanum tuberosum L.

The first step of methionine biosynthesis in higher plants, the condensatio n of O-phosphohomoserine and L-cysteine forming the thioether cystathionine , is catalyzed by the enzyme cystathionine gamma-synthase (CgS). We have is olated a cDNA encoding CgS from a leaf lambda ZAP II-library of Solanum tub erosum L. The nucleotide and deduced amino acid sequence showed homology to the other CgS sequences from Arabidopsis thaliana, Zea mays, Mesembryanthe mum crystallinum and Fragaria vesca. The truncated cDNA without putative le ader peptide, when cloned into a bacterial expression vector, complemented the E. coli metB1 mutant strain LE392. Enzyme activity of the potato CgS an d E. coli metB were comparable in the auxotrophic background. Transcript le vels of CgS in different tissues of potato plants were determined by Northe rn blot analysis. Expression was found in all tissues with elevated levels in flowers and source leaves. The pattern of gene expression during a day/n ight period implied light-dependent control of CgS transcription typical fo r enzymes localized in plastids. The expression of CgS was shown to be ligh t-inducible.