Expression of threonine synthase from Solanum tuberosum L. is not metabolically regulated by photosynthesis-related signals or by nitrogenous compounds

Although the control of carbon fixation and nitrogen assimilation has been studied in detail, little is known about the regulation of carbon and nitro gen flow into amino acids. In this paper the isolation of a cDNA encoding t hreonine synthase is reported (TS; EC 4.2.99.2) from a leaf lambda ZAP II-l ibrary of Solanum tuberosum L. and the transcriptional regulation of the re spective gene expression in response to metabolic changes. The pattern of e xpression of TS by feeding experiments of detached petioles revealed that T S expression is regulated neither by photosynthesis-related metabolites nor by nitrogenous compounds. The present study suggests that the regulation o f the conversion of aspartate to threonine is not controlled at the transcr ipt level of TS. The nucleotide and deduced amino acid sequences of potato TS show homology to other known sequences from Arabidopsis thaliana and mic roorganisms. TS is present as a low copy gene in the genome of potato as de monstrated in Southern blot analysis. When cloned into a bacterial expressi on vector, the cDNA did functionally complement the Escherichia coli mutant strain Gif41. TS transcript was found in all tissues of potato and was mos t abundant in flowers and source leaves. (C) 2000 Elsevier Science Ireland Ltd, All rights reserved.