Genes encoding for branched-chain amino acid aminotransferase are differentially expressed in plants

The final metabolic step in the production of the amino acids leucine, isoleucine and valine is a transamination reaction catalyzed by the enzyme branched-chain amino acid aminotransferase (BCAT). Using complementation of an Escherichia coli ilvE mutant we have isolated two different cDNAs from potato (Solanum tuberosum) encoding for BCAT (BCAT1 and BCAT2). BCAT1 and BCAT2 were 86 % identical to each other based on deduced amino acid sequence. Southern analysis indicated that BCAT1 and BCAT2 are not in identical regions of the genome and that BCAT1 may exist in multiple copies. The deduced amino acid sequences for both cDNAs contained putative transit peptides for plastid or mitochondrial localization demonstrating spatial expression of the gene products. Northern analysis showed an induction of BCAT1, relative to BCAT2, in leaf tissues exposed to proliferative hormone treatments suggesting that a response to increased growth, and the need for branched-chain amino acid metabolism associated with that growth, is limited to the expression of BCAT1.