Genome-Wide Identification, Classification, and Expression Analysis of the HD-Zip Transcription Factor Family in Apple ( Borkh.).

Homeodomain-leucine zipper () family genes are considered to play an important role in plant growth and stress tolerance. However, a genome-wide analysis of genes in apples ( Borkh.) has not been performed. We detected 48 genes in the apple genome, and categorized them into three subfamilies on the basis of phylogenetic analysis. The chromosomal locations, gene/protein structures, and physiological and biochemical properties of these genes were analyzed. Synteny analysis revealed that segmental duplications were key in the expansion of the apple HD-Zip family. According to an analysis of cis-regulatory elements and tissue-specific expression patterns, genes may be widely involved in the regulation of apple growth and tolerance to environmental stresses. Furthermore, the transcript levels of apple I and II genes were up-regulated in response to fungal treatments. Expression of apple Ⅲ genes was enhanced during adventitious bud regeneration. This suggested possible roles of these genes in regulating the apple response to fungal infection, as well as adventitious bud regeneration. The current results may help us to better understand the evolution and function of apple genes, and thus facilitate further research on plant resistance to fungal infection and in vitro regeneration.