Data_Sheet_1_MdHB-7 Regulates Water Use Efficiency in Transgenic Apple (Malus domestica) Under Long-Term Moderate Water Deficit.docx

Improved water use efficiency (WUE) promotes plant survival and crop yield under water deficit conditions. Although the plant-specific HD-Zip I transcription factors have important roles in plant adaptation to various abiotic stresses, including water deficit, their functions in regulating WUE of apple (Malus domestica) are poorly understood. We characterized the role of MdHB-7 in WUE regulation by subjecting MdHB-7 transgenic plants to long-term moderate soil water deficit. The long-term WUE (WUEL) of transgenic apple plants with MdHB-7 overexpression or MdHB-7 RNA interference (RNAi) differed significantly from that of control plants. Upregulation of MdHB-7 caused reduced stomatal density, whereas the suppression of MdHB-7 increased stomatal density under both normal and long-term moderate soil water deficit conditions. Moderate reduction in stomatal density helped to improve the WUE of MdHB-7 overexpression transgenic plants, especially under water deficit conditions. MdHB-7 overexpression plants maintained high rates of photosynthesis that were conducive to the accumulation of biomass and the improvement of WUEL. MdHB-7 overexpression also alleviated the inhibition of root growth caused by long-term moderate soil water deficit and improved root vitality and hydraulic conductivity, which were essential for improving plant WUEL. By contrast, MdHB-7 RNA interference reduced the WUEL of transgenic plants by inhibiting these factors under normal and long-term moderate soil water deficit conditions. Taken together, our results provide solid evidence for a crucial role of MdHB-7 in the regulation of apple WUEL and provide new insights for improving the WUE of apple plants under moderate soil water deficit.

水分利用效率（water use efficiency, WUE）的提升可促进缺水条件下植物存活与作物产量提升。尽管植物特异性同源异型域-亮氨酸拉链I类（HD-Zip I）转录因子在植物适应包括水分匮乏在内的多种非生物胁迫中发挥重要作用，但目前对于其调控苹果（Malus domestica）水分利用效率的功能尚不清楚。本研究通过将MdHB-7转基因植株置于长期适度土壤缺水条件下，解析了MdHB-7在调控水分利用效率中的功能。过表达MdHB-7或MdHB-7 RNA干扰（RNA interference, RNAi）的转基因苹果植株，其长期水分利用效率（long-term WUE, WUEL）与对照植株存在显著差异。在正常培养与长期适度土壤缺水条件下，MdHB-7的上调表达会降低气孔密度，而MdHB-7的表达抑制则会提升气孔密度。适度降低气孔密度有助于提升MdHB-7过表达转基因植株的水分利用效率，在缺水条件下这一效果尤为显著。MdHB-7过表达植株可维持较高的光合速率，这有利于生物量积累与长期水分利用效率的提升。MdHB-7过表达还可缓解长期适度土壤缺水对根系生长的抑制，提升根系活力与导水率，而这些均是提升植株长期水分利用效率的关键因素。与之相反，在正常培养与长期适度土壤缺水条件下，MdHB-7 RNA干扰会通过抑制上述过程降低转基因植株的长期水分利用效率。综上，本研究结果为MdHB-7在调控苹果长期水分利用效率中的关键作用提供了确凿证据，并为提升适度土壤缺水条件下苹果植株的水分利用效率提供了新的研究思路。