MOLECULAR CHARACTERIZATION OF THE CO GENE REGION IN MALUS × DOMESTICA
The columnar phenotype in apple is characterized by a stunted growth with short internodes and lateral branches being converted into fruit spurs. Columnar growth is due to a spontaneous mutation in the cultivar McIntosh discovered in the 1960s. It seems to be controlled by a single dominant allele of the Co gene, which displays a typical Mendelian way of inheritance. So far all tested columnar apple trees had the Co gene in an heterozygous state. We developed PCR assays on the basis of molecular markers closely linked to the Co gene by screening the F1 progeny of a cross between a columnar and a non-columnar cultivar. These markers, combined with markers published earlier by other groups, allowed us to define a genomic region of approximately 1 Mbp on chromosome 10 probably containing the Co locus. In order to analyze this region in detail we constructed several genomic BAC libraries of a columnar cultivar. The BAC libraries consisted of more than 100,000 clones representing about 4x haploid apple tree genome equivalents. PCR-based screening and colony filter hybridization of the BAC libraries delivered about 37 BAC clones originating from the Co region. These clones were sequenced using a combination of Sanger and Illumina next generation sequencing. These sequences were assembled into a contig spanning most of the Co region. Selected genes from this region were analyzed in detail with regard to gene structure and single nucleotide polymorphisms to identify potential candidate genes for the Co gene. 24 genes displayed mutations leading to amino acid substitutions in the columnar growing cultivar and hence are considered as candidates for the Co gene.
Otto, D., Petersen, R., Krost, C., Schmidt, E.R., Brandl, R., Brauksiepe, B. and Braun, P. (2014). MOLECULAR CHARACTERIZATION OF THE CO GENE REGION IN MALUS × DOMESTICA. Acta Hortic. 1048, 87-95
apple, BAC library, Co gene, columnar growth, molecular markers, NGS