The NAC transcription factor MdNAC29 negatively regulates drought tolerance in apple

Drought stress is an adverse stimulus that affects agricultural production worldwide. NAC transcription factors are not only commonly involved in plant development and growth, but also play different roles in abiotic stress response. Here, we isolated the apple MdNAC29 gene, and its role in regulating drought stress was investigated. Subcellular localization experiments showed that MdNAC29 was localized to the nucleus and the transcription level was induced by drought treatment. Over-expression of MdNAC29 reduced drought tolerance in apple plants, calli and tobacco, and exhibited higher relative conductivity, malondialdehyde (MDA) content and lower Chlorophyll content under drought stress. The transcriptomic analyses showed that MdNAC29 might reduce drought resistance by modulating the expression of photosynthesis and leaf senescence related genes. The qRT-PCR results showed that overexpression of MdNAC29 represses the expression of drought resistance genes. Yeast one-Hybrid (Y1H) and Dual-Luciferase (Luc) assays demonstrated that MdNAC29 directly repressed the expression of MdDREB2A. Moreover, Yeast Two-Hybrid (Y2H) assays and Bimolecular Fluorescence Complementation (BiFC) assays demonstrated that MdNAC29 interacted with the F-box protein PP2-B10-like (MdPP2-B10), which is responded to drought stress. Taken together, our results indicate that MdNAC29 plays a negative regulator in the drought resistance, which can provide theoretical basis for further molecular mechanism research.

干旱胁迫是威胁全球农业生产的一类逆境胁迫因子。NAC转录因子（NAC transcription factors）不仅广泛参与植物生长发育过程，还在非生物胁迫响应中发挥多样化调控功能。本研究分离得到苹果MdNAC29基因，并对其在干旱胁迫调控中的作用展开系统探究。亚细胞定位实验结果显示，MdNAC29定位于细胞核，且其转录水平可被干旱处理诱导上调。将MdNAC29过表达后，苹果植株、愈伤组织及烟草的耐旱性均显著降低，干旱胁迫下其相对电导率、丙二醛（malondialdehyde, MDA）含量均升高，而叶绿素含量则下降。转录组分析表明，MdNAC29可能通过调控光合作用与叶片衰老相关基因的表达，削弱植株的抗旱能力。实时荧光定量PCR（qRT-PCR）结果显示，MdNAC29过表达会抑制抗旱相关基因的转录。酵母单杂交（Yeast one-Hybrid, Y1H）与双荧光素酶（Dual-Luciferase, Luc）实验证实，MdNAC29可直接靶向抑制MdDREB2A的表达。此外，酵母双杂交（Yeast Two-Hybrid, Y2H）与双分子荧光互补（Bimolecular Fluorescence Complementation, BiFC）实验进一步证明，MdNAC29可与响应干旱胁迫的F-box蛋白PP2-B10-like（MdPP2-B10）发生特异性相互作用。综上，本研究结果表明MdNAC29作为负调控因子参与植物抗旱调控，该发现可为后续深入解析其分子作用机制提供重要理论基础。