COMPARATIVE GENOMICS OF THE EVERGROWING LOCUS AMONG APRICOT, PEACH AND POPLAR

Abstract

The evergrowing (evg) mutant of peach [Prunus persica (L.) Batsch] fails to cease growth and enter dormancy under dormancy-inducing conditions. The EVG locus has been mapped and sequenced in wild-type peach. Six dormancy associated MADS-box (DAM) genes have been found in this locus and proposed as candidates for the regulation of growth cessation and terminal bud formation in peach in response to dormancy-inducing conditions. To study the duplication history of the DAM genes, we identified two BACs corresponding to the EVG locus in apricot (P. armeniaca L.) by southern hybridization. We sequenced and annotated a 70 kb region that contains five predicted DAM genes in apricot. We compared the peach EVG locus by global pair-wise alignment with the 70 kb apricot sequence, and the Arabidopsis [Arabidopsis thaliana (L.) Heynh.] and poplar (Populus trichocarpa Torr. & A. Gray) sequenced genomes. The phylogenetic relationships among DAM genes were also studied. As expected, there was a strong similarity between peach and apricot genomic sequence with a conserved order and orientation of orthologous genes. The peach EVG locus had sequence similarity to three loci in poplar reflecting a different duplication history. Greater synteny between the peach EVG locus and the poplar loci was found, than between peach and Arabidopsis. DAM gene phylogeny and locus distribution in the respective genomes indicates that duplication of the DAM genes occurred after Prunus and poplar divergence. Our data suggest that poplar is a better model than Arabidopsis for predicting gene presence and order with Prunus although the large scale duplication history of poplar will complicate the comparison.