PLASTID-LOCALIZED ACETYL-COA CARBOXYLASE OF BREAD WHEAT IS ENCODED BYA SINGLE-GENE ON EACH OF THE 3 ANCESTRAL CHROMOSOME SETS

5'-End fragments of two genes encoding plastid-localized acetyl-CoA ca rboxylase (ACCase; EC 6.4.1.2) of wheat (Triticum aestivum) were clone d and sequenced. The sequences of the two genes, Ace-1,I and Ace-1,2, are 89% identical. Their exon sequences are 98% identical. The amino a cid sequence of the biotin carboxylase domain encoded by Acc-1,I and A cc-1,2 is 93% identical with the maize plastid ACCase but only 80-84% identical with the cytosolic ACCases from other plants and from wheat. Four overlapping fragments of cDNA covering the entire coding region were cloned by PCR and sequenced. The wheat plastid ACCase ORF contain s 2,311 amino acids with a predicted molecular mass of 255 kDa. A puta tive transit peptide is present at the N terminus. Comparison of the g enomic and cDNA sequences revealed introns at conserved sites found in the genes of other plant multifunctional ACCases, including two intro ns absent from the wheat cytosolic ACCase genes. Transcription start s ites of the plastid ACCase genes were estimated from the longest cDNA clones obtained by 5'-RACE (rapid amplification of cDNA ends). The unt ranslated leader sequence encoded by the Ace-1 genes is at least 130-1 70 nucleotides long and is interrupted by an intron. Southern analysis indicates the presence of only one copy of the gene in each ancestral chromosome set. The gene maps near the telomere on the short arm of c hromosomes 2A, 2B, and 2D. Identification of three different cDNAs, tw o corresponding to genes Acc-1,I and Acc-1,2, indicates that all three genes are transcriptionally active.