Evidence for regulation of columnar habit in apple encodes a putative 2og-fe(ii) oxygenase

Understanding the genetic mechanisms controlling columnar-type growth in the apple mutant Wijcik will provide insights on how tree architecture and growth are regulated in fruit trees. In apple, columnar-type growth is controlled by a single major gene at the Columnar (Co) locus. By comparing the genomic sequence of the Co region of Wijcik with its wild-type McIntosh, a novel non-coding DNA element of 1956 bp specific to Pyreae was found to be inserted in an intergenic region of Wijcik. Expression analysis of selected genes located in the vicinity of the insertion revealed the upregulation of the MdCo31 gene encoding a putative 2OG-Fe(II) oxygenase in axillary buds of Wijcik. Constitutive expression of MdCo31 in Arabidopsis thaliana resulted in compact plants with shortened floral internodes, a phenotype reminiscent of the one observed in columnar apple trees. We conclude that MdCo31 is a strong candidate gene for the control of columnar growth in Wijcik