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

• Published in: Frontiers in plant science Vol. 12; p. 740492
• Main Authors: Zhao, Shuang, Gao, Hanbing, Jia, Xumei, Wei, Jiangtong, Mao, Ke, Ma, Fengwang
• Format: Journal Article
• Language: English
• Published: Frontiers Media S.A 28.10.2021
• Subjects: long-term moderate soil water deficit; Malus domestica; MdHB-7; Plant Science; root; stomatal density; water use efficiency
• ISSN: 1664-462X; 1664-462X
• DOI: 10.3389/fpls.2021.740492

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 (WUE L ) 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 WUE L . 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 WUE L . By contrast, MdHB-7 RNA interference reduced the WUE L 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 WUE L and provide new insights for improving the WUE of apple plants under moderate soil water deficit.