Genome-wide analysis of histone deacetylases in Apple and functional analysis of MdHDA6 in drought and salt stress responses

Histone acetylation controlled by a pair of antagonistic enzymes histone acetyltransferases (HATs) and histone deacetylases (HDACs) widely regulates various biological processes. In the view of involvements of HDACs in plant development and stress responses, we genome-widely identified HDACs in Apple (MdHDACs) and performed comprehensive analyses of these MdHDACs. Firstly, we identified 26 predicted MdHDAC genes in Apple genome and the phylogenetic analysis divided them into three distinct categories. Their introns/exon structure, conserved motifs and domain architecture were further analyzed. According to the RNA-seq data, we analyzed the expression patterns of MdHDACs during the Apple development and stress responses. The results showed that the expression levels of MdHDACs were dynamic during the flower morphogenesis, male gametocytogenesis, embryonic development, new bud phloem and fruit development, implying their regulatory roles in these processes. We also found that the mRNA abundances of MdHDAs responded to the various abiotic stresses, including drought, cold and salt stresses. Additionally, we selected a candidate gene MdHDA6 and ectopically expressed it in tobacco to investigate its functions in response to drought and salt stresses. Our results showed that MdHDA6-overexpression tobacco decreases the drought and salt tolerances by regulating the expression of resistance genes. Our data reveal a comprehensive fundamental analysis of histone deacetylases HDACs in Apple and provide the basis of further investigation of MdHDACs in Apple development and stress responses.