Recurrent single-gene duplication drives the expansion and expression diversification of the ADH gene family in pear and other Rosaceae species

Background: Alcohol dehydrogenases (ADHs) are essential to plant growth and the formation of aromatic compounds in fruits. However, the evolutionary history and characteristics of ADH gene expression remain largely unclear in Chinese white pear ( Pyrus bretschneideri ) and other fruit species from the family Rosaceae.Results In this study, 464 ADH genes were identified in eight Rosaceae fruit species and 68 of the genes were from pear. Based on the analyses of phylogeny and conserved motifs, the pear ADH genes were classified into four subgroups (I, II, III, and IV). The chromosomal distribution of the genes was found to be uneven and numerous clusters of physically linked ADH genes were detected. Frequent single-gene duplication events were found to have contributed to the formation of ADH gene clusters and the expansion of the ADH gene family in these eight Rosaceae species. Purifying selection was the major force in ADH gene evolution. The younger genes derived from tandem and proximal duplications had evolved faster than those that derived from other types of duplication. RNA-sequencing and quantitative-real time-PCR analysis revealed that the expression levels of three ADH genes were closely correlated with the content of aromatic compounds that are found during fruit development.Conclusion Comprehensive analyses were conducted in eight Rosaceae species and 464 ADH genes were identified. The results of this study provide new insights into the evolution and expression characteristics of ADH family genes in pear and other Rosaceae species.