The MdARF7/19-MdBBM1 module mediates auxin signaling to regulate the formation of adventitious roots in self-rooted apple stocks

Self-rooted apple stocks are the main recommended stocks for high-standard orchard construction in China. However, the few adventitious roots (ARs) in self-rooted apple stocks have restricted the high-quality development of the apple industry. BABY BOOM (BBM) plays a key role in the regeneration and transformation of plants. BBM1 was known to regulate ARs formation, was affected by auxin. However, the role of MdBBM1 in the formation of self-rooted apple stocks ARs remains unclear. Therefore, it is particularly necessary to clarify the molecular mechanism of MdBBM1-mediated ARs formation in self-rooted apple stocks. In this study, the MdARF7 and MdARF19 were revealed, two auxin-responsive transcription factors in response to auxin signaling, directly activate MdBBM1 expression via bind to its promoter, thereby promoting the self-rooted apple stocks ARs formation. Overexpression of MdBBM1 significantly enhances ARs development in self-rooted apple stocks, confirming its functional importance. Furthermore, we demonstrate that MdARF7 interacts with MdRH53, suggesting an additional regulatory layer in adventitious root formation. Collectively, our findings establish a novel auxin-MdARF7/19-MdBBM1 regulatory module that regulates ARs development in self-rooted apple stocks.