Apple rootstock dwarfing and dense planting are common practices in apple farming. However, the dwarfing mechanisms are not understood. In this study, the expression of MdARF3 in the root system of dwarfing rootstock 'M9' was lower than in the vigorous rootstock from Malus micromalus due to the deletion of the WUSATAg element in the promoter of the 'M9' genotype. Notably, this deletion variation was significantly associated with dwarfing rootstocks. Subsequently, transgenic tobacco (Nicotiana tabacum) cv. Xanthi was generated with the ARF3 promoter from 'M9' and M. micromalus genotypes. The transgenic apple with 35S:: MdARF3 was also obtained. The transgenic tobacco and apple with the highly expressed ARF3 had a longer root system and a higher plant height phenotype. Furthermore, the yeast one-hybrid, luciferase, electrophoretic mobility shift assays, and Chip-qPCR identified MdWOX4-1 in apples that interacted with the pMm-ARF3 promoter but not the pM9-ARF3 promoter. Notably, MdWOX4-1 significantly increased the transcriptional activity of MdARF3 and MdLBD16-2. However, MdARF3 significantly decreased the transcriptional activity of MdLBD16-2. Further analysis revealed that MdARF3 and MdLBD16-2 were temporally expressed during different stages of lateral root development. pMdLBD16-2 was mainly expressed during the early stage of lateral root development, which promoted lateral root production. On the contrary, pMmARF3 was expressed during the late stage of lateral root development to promote elongation. The findings in this study will shed light on the genetic causes of apple plant dwarfism and provide strategies for molecular breeding of dwarfing apple rootstocks.

中文翻译：

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MdARF3 改变侧根伸长以调节苹果植物的矮化

苹果砧木矮化和密植是苹果种植的常见做法。然而，矮化机制尚不清楚。在本研究中，由于“M9”基因型启动子中WUSATAg元件的缺失，矮化砧木“M9”根系中MdARF3的表达低于Malus micromalus的旺盛砧木。值得注意的是，这种缺失变异与矮化砧木显着相关。随后，转基因烟草（Nicotiana tabacum）cv。Xanthi 是用来自“M9”和 M. micromalus 基因型的 ARF3 启动子生成的。还获得了带有35S::MdARF3的转基因苹果。高表达ARF3的转基因烟草和苹果具有更长的根系和更高的株高表型。此外，酵母单杂交、荧光素酶、电泳迁移率变动分析和 Chip-qPCR 鉴定出苹果中的 MdWOX4-1 与 pMm-ARF3 启动子相互作用，但不与 pM9-ARF3 启动子相互作用。值得注意的是，MdWOX4-1 显着增加了 MdARF3 和 MdLBD16-2 的转录活性。然而，MdARF3 显着降低了 MdLBD16-2 的转录活性。进一步分析发现，MdARF3和MdLBD16-2在侧根发育的不同阶段短暂表达。pMdLBD16-2主要在侧根发育早期表达，促进侧根产生。相反，pMmARF3在侧根发育后期表达，促进伸长。本研究的结果将揭示苹果植株矮化的遗传原因，并为苹果矮化砧木的分子育种提供策略。