Investigating the Mechanisms of Adventitious Root Formation in Semi-Tender Cuttings of Prunus mume: Phenotypic, Phytohormone, and Transcriptomic Insights

Mei (<i>Prunus mume</i> Sieb. et Zucc.) is a rare woody species that flowers in winter, yet its large-scale propagation is limited by the variable ability of cuttings to form adventitious roots (ARs). In this study, two cultivars were compared: <i>P. mume</i> 'Xiangxue Gongfen' (GF), which roots readily, and <i>P. mume</i> 'Zhusha Wanzhaoshui' (ZS), which is more recalcitrant. Detailed anatomical observations revealed that following cutting, the basal region expanded within 7 days, callus tissues had appeared by 14 days, and AR primordia emerged between 28 and 35 days. Notably, compared to the recalcitrant cultivar ZS, the experimental cultivar GF exhibited significantly enhanced callus tissue formation and AR primordia differentiation. Physiological analyses showed that the initial IAA concentration was highest at day 0, whereas cytokinin (tZR) and gibberellin (GA1) levels peaked at 14 days, with ABA gradually decreasing over time, resulting in increased IAA/tZR and IAA/GA1 ratios during the rooting process. Transcriptomic profiling across these time points identified significant upregulation of key genes (e.g., <i>PmPIN3</i>, <i>PmLOG2</i>, <i>PmCKX5</i>, <i>PmIAA13</i>, <i>PmLAX2</i>, and <i>PmGA2OX1</i>) and transcription factors (<i>PmWOX4</i>, <i>PmSHR</i>, and <i>PmNAC071</i>) in GF compared to ZS. Moreover, correlation analyses revealed that <i>PmSHR</i> expression is closely associated with IAA and tZR levels. Overexpression of <i>PmSHR</i> in tobacco further validated its role in enhancing lateral root formation. Together, these findings provide comprehensive insights into the temporal, hormonal, and genetic regulation of AR formation in <i>P. mume</i>, offering valuable strategies for improving its propagation.