The homeodomain-leucine zipper (HD-Zip) family has been shown to perform a multitude of functions during plant development and stress responses; however, the family members and functions have not been identified in apple (Malus × domestica). In this study, 83 HD-Zips (MdHDZs) were identified in the apple genome. They were assembled into four subgroups according to the classification in Arabidopsis, where MdHDZs in the same subgroup had similar gene structures and conserved protein motifs. Putative cis-element analysis of MdHDZs promoter regions uncovered numerous elements related to the response of stress and plant hormones. In addition, twelve transcripts of the MdHDZs showed different expression patterns under salt, drought, low temperature and ABA stresses by quantitative reverse transcription-PCR (qRT-PCR) assay. To further explore the function of MdHDZs in apple, MdHDZ3 was selected to verify its function under salt, low temperature and ABA stresses; and genetic transformation was used to obtain MdHDZ3 transgenic apple calli. The results demonstrated that MdHDZ3 increased sensitivity to salt, low temperature and abscisic acid in apple calli, suggesting that MdHDZ3 plays an important role in response to stresses. Subcellular localization and three-dimensional structural analysis revealed that MdHDZ3 was a nuclear-localized protein. Taken together, these findings provide potential information for further identification of HD-Zip proteins in apple.

同源域亮氨酸拉链 (HD-Zip) 家族已被证明在植物发育和应激反应过程中发挥着多种功能。然而，苹果（ Malus × domestica）的家族成员和功能尚未确定。在这项研究中，在苹果基因组中鉴定了 83 个 HD-Zips (MdHDZ)。根据拟南芥中的分类将它们组装成四个亚组，其中同一亚组中的MdHDZ具有相似的基因结构和保守的蛋白质基序。MdHDZs启动子区域的推定顺式元素分析揭示了许多与胁迫和植物激素反应相关的元素。此外，MdHDZ的 12 个转录本通过定量逆转录PCR（qRT-PCR）测定显示在盐，干旱，低温和ABA胁迫下的不同表达模式。为进一步探索苹果中MdHDZs的功能，选择MdHDZ3对其在盐、低温和ABA胁迫下的功能进行验证；并通过遗传转化获得MdHDZ3转基因苹果愈伤组织。结果表明，MdHDZ3增加了苹果愈伤组织对盐分、低温和脱落酸的敏感性，表明MdHDZ3在胁迫响应中起重要作用。亚细胞定位和三维结构分析表明，MdHDZ3 是一种核定位蛋白。总之，这些发现为进一步鉴定苹果中的 HD-Zip 蛋白提供了潜在信息。