Transcriptional regulation of MdPIN7 by MdARF19 during gravity-induced formation of adventitious root GSA in self-rooted apple stock

Self-rooted apple stock is widely used for apple production. However, the shallowness of the adventitious roots in self-rooted apple stock leads to poor performance in the barren orchards of China. This is because of the considerable difference in the development of a gravitropic set-point angle (GSA) between self-rooted apple stock and seedling rootstock. Therefore, it is crucial to study the molecular mechanism of adventitious root GSA in self-rooted apple stock for breeding self-rooted and deep-rooted apple rootstock cultivars. An apple auxin response factor MdARF19 functioned to establish the adventitious root GSA of self-rooted apple stock in response to gravity and auxin signals. MdARF19 bound directly to the MdPIN7 promoter, activating its transcriptional expression and thus regulating the formation of the adventitious root GSA in 12-2 self-rooted apple stock. However, MdARF19 influenced the expression of auxin efflux carriers (MdPIN3 and MdPIN10) and the establishment of adventitious root GSA of self-rooted apple stock in response to gravity signals by direct activation of MdFLP. Our findings provide new information on the transcriptional regulation of MdPIN7 by auxin response factor MdARF19 in the regulation of the adventitious root GSA of self-rooted apple stock in response to gravity and auxin signals.