Submitted to: Molecular Biology and Evolution
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/14/2001
Publication Date: 8/15/2001
Citation: Faris, J.D., Sirikhachornkit, A., Haselkorn, R., Gill, B., Gornicki, P. 2001. Chromosome mapping and phylogenetic analysis of the cytosoloc acetyl-coa carboxylase loci in wheat. Molecular Biology and Evolution 18:1720-1733. Interpretive Summary: Common bread wheat is one of the worlds most important crops, and it has a relatively complex genome compared to other crop species. Wheat evolved through the convergence of three ancestral grass species with relatively simple genomes. In recent decades, wheats progenitor species have been identified through various studies. We examined the DNA sequence of a gene (Acc-2) for acetyl-CoA carboxylase (ACCase), which is involved in the synthesis of fatty acids and plant metabolism, in wheat and its relatives to gain insights of molecular evolutionary events that have been involved in shaping the wheat genome. We determined the chromosome location of the Acc-2 genes in wheat and the DNA sequence of Acc-2 genes from wheat and its relatives. We also reconstructed a family tree based on the DNA of the Acc-2 genes. We found that wheat contains multiple copies of the Acc-2 gene that differ only slightly in their DNA sequence, but most of the copies were located very near each other on the same chromosome. Some of the copies were inherited from the progenitor species and some were the result of evolutionary gene duplication events. Other evolutionary events involved the translocation of some copies to different chromosome locations and loss of portions of the genes. The family tree and the relationship of wheat with its relatives agreed with previous studies by other researchers. This study provided insights into evolutionary genome-shaping events at the molecular level and a better understanding of the structure of the wheat genome.
Technical Abstract: The cytosolic isoform of plant acetyl-CoA carboxylase is a multi-domain enzyme involved in the synthesis of very long chain fatty acids and in secondary metabolism. Chromosome mapping of wheat identified one locus containing cytosolic acetyl-CoA carboxylase genes (Acc-2) and a related partially processed pseudogene (Y-Acc-2) in the distal region of the long arm of wheat homoeologous group 3 chromosomes. Multiple copies of the Acc-2 genes are likely to be arranged in tandem repeats. At least three out of five genes cloned from hexaploid wheat map to this locus. Another locus containing Acc-2 related sequences is present in the distal region of the long arm of chromosome 5D. A system based on PCR-cloning and DNA sequence analysis of acetyl-CoA carboxylase genes was developed to address various phylogenetic and systematics questions in grasses. It was applied to reconstruct the phylogeny of the Acc-2 genes from D- and S-genome Aegilops and A-genome Triticum diploid species, AABB- and AAGG-genome tetraploid wheat and AABBDD-genome hexaploid wheat as well as from rye and barley. The combined cytogenetic and molecular evolution approach allowed assignment of gene sequences included in phylogenetic analysis to specific loci on homoeologous chromosomes. Recurring gene duplication followed by chromosome translocation and/or possible loss of some gene copies as well as loss of introns occurred in the gene family in different plant lineages. Two major Acc-2 clades appeared before the divergence of barley and rye. This analysis of the Acc-2 loci provides detailed information regarding evolutionary events at a low copy-number locus containing important functional genes. These events are likely to be common and to play a significant role in shaping grass genomes.