Molecular Mechanisms Underlying the Differences in Rooting Traits Between <i>Populus yunnanensis</i> and <i>Populus davidiana</i>

Adventitious roots (ARs) are vital for the propagation of forest cuttings, but rooting difficulties limit the usage of some species. Despite AR growth mechanisms having been extensively studied, it is still unknown what mechanisms underlie the variations in AR generating capacities among species. The transcriptomes of Populus davidiana (difficult-to-root) and Populus yunnanensis (easy-to-root) at different periods after cutting were compared in the present study. It was found that most auxin and cytokinin-related genes were up-regulated in P. yunnanensis, while they were down-regulated in P. davidiana. Among the differentially expressed transcription factors (TFs), P. yunnanensis had higher expression levels of genes linked to AR development than P. davidiana. At 96 and 120 h after cuttings, the WOX genes displayed notable alterations. Further investigation of the WOX gene families in P. yunnanensis and P. davidiana showed that they were grouped into three branches. Cis-regulatory elements (CREs) analysis revealed that PyunWOXs exhibited more extensive activities than PdaWOXs. Additionally, gene expression profiling revealed that WOX11 expression peaked at the early initiation stage of rooting. Overexpression of WOX11 significantly promoted the increase in the number of ARs. In summary, WOX11 played a positive regulatory role in the growth of ARs.