Improving plant drought tolerance and water-use efficiency (WUE) is important for plant survival and crop yield under conditions of water shortage. HD-Zip transcription factors (TFs) have been shown to help plants respond to drought. Here, MdHB7-like (an HD-Zip I TF) was identified as a drought-induced gene in apple plants. Transgenic apple with upregulated expression of MdHB7-like showed enhanced drought tolerance, whereas MdHB7-like RNA interference (RNAi) lines were more sensitive to drought. Further analysis showed that overexpression of MdHB7-like reduced stomatal density, but the stomatal density of MdHB7-like RNAi lines was increased. Transcriptome analysis showed that MdHB7-like overexpressing plants may reduce stomatal density by affecting the expression of stomatal development related genes, such as MdEPFL9.1 and MdEPFL9.2. The decrease in stomatal density reduced leaf water loss, helping to enhance the drought tolerance of overexpression lines. In addition, MdHB7-like overexpression enhanced drought tolerance of apple plants by promoting stomatal closure. Further study showed that the overexpression of MdHB7-like significantly increased WUE under long-term moderate drought conditions, which also related to the reduction of stomatal density. These results suggest that MdHB7-like is a valuable genetic resource for enhancing drought tolerance and increasing the WUE of apple germplasm.

提高植物的耐旱性和水分利用效率（WUE）对于缺水条件下的植物生存和作物产量很重要。HD-Zip 转录因子 (TF) 已被证明可以帮助植物应对干旱。在这里，MdHB7 样（HD-Zip I TF）被鉴定为苹果植物中的干旱诱导基因。MdHB7 样表达上调的转基因苹果显示出增强的耐旱性，而MdHB7 样RNA 干扰 (RNAi) 系对干旱更敏感。进一步的分析表明，MdHB7-like 的过表达降低了气孔密度，但MdHB7-like RNAi 系的气孔密度增加。转录组分析表明MdHB7 样过表达植物可能通过影响气孔发育相关基因的表达，如MdEPFL9.1和MdEPFL9.2来降低气孔密度。气孔密度的降低减少了叶片失水，有助于增强过表达系的耐旱性。此外，MdHB7 样过表达通过促进气孔关闭增强了苹果植物的耐旱性。进一步研究表明，在长期中度干旱条件下，MdHB7-like的过表达显着增加了WUE，这也与气孔密度降低有关。这些结果表明MdHB7 样 是提高苹果种质耐旱性和提高 WUE 的宝贵遗传资源。