The dwarfing rootstocks-mediated high-density apple orchard is becoming the main practice management. Currently, dwarfing rootstocks are widely used worldwide, but their shallow root system and drought sensitivity necessitate high irrigation requirements. Here, the root transcriptome and metabolome of dwarfing (M9-T337, a drought-sensitive rootstock) and vigorous rootstocks (Malus sieversii, a drought-tolerant species, is commonly used as a rootstock) showed that a coumarin derivative, 4-Methylumbelliferon (4-MU), was found to accumulate significantly in the roots of vigorous rootstock under drought condition. When exogenous 4-MU was applied to the roots of dwarfing rootstock under drought treatment, the plants displayed increased root biomass, higher root-to-shoot ratio, greater photosynthesis, and elevated water use efficiency. In addition, diversity and structure analysis of the rhizosphere soil microbial community demonstrated that 4-MU treatment increased the relative abundance of putatively beneficial bacteria and fungi. Of these, Pseudomonas, Bacillus, Streptomyces, and Chryseolinea bacterial strains and Acremonium, Trichoderma, and Phoma fungal strains known for root growth, or systemic resistance against drought stress, were significantly accumulated in the roots of dwarfing rootstock after 4-MU treatment under drought stress condition. Taken together, we identified a promising compound—4-MU, as a useful tool, to strengthen the drought tolerance of apple dwarfing rootstock.

中文翻译：

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4-甲基伞形酮（4-MU）通过调节根际微生物多样性和根系结构增强苹果的耐旱性

以矮化砧木为主导的高密度苹果园正在成为主要的管理方式。目前，矮化砧木在世界范围内广泛使用，但其根系浅且对干旱敏感，需要较高的灌溉要求。在此，矮化砧木（M9-T337，一种干旱敏感砧木）和旺盛砧木（Malus sieversii，一种耐旱物种，通常用作砧木）的根转录组和代谢组显示，香豆素衍生物 4-甲基伞形酮（ 4-MU），被发现在干旱条件下在旺盛的砧木的根部显着积累。当在干旱处理下将外源4-MU施用于矮化砧木的根部时，植物表现出增加的根生物量、更高的根冠比、更强的光合作用和更高的水分利用效率。此外，根际土壤微生物群落的多样性和结构分析表明，4-MU 处理增加了假定有益细菌和真菌的相对丰度。其中，假单胞菌属、芽孢杆菌属、链霉菌属和金黄菌属菌株以及枝顶孢霉属、木霉属和茎点霉属真菌菌株以根部生长或对干旱胁迫的系统抵抗力而闻名，在干旱条件下经过 4-MU 处理后，在矮化砧木的根部显着积累应激状态。综上所述，我们发现了一种有前途的化合物——4-MU，作为增强苹果矮化砧木耐旱性的有用工具。