PabIAA33-PabARF16 module regulates PabWOX13 expression to promote adventitious root formation in poplar cuttings

Aspen trees (section Populus) exhibit a weaker capability of adventitious roots formation during cutting propagation relative to other poplar sections. Although it is known that adventitious root formation depends on the potential for root primordium induction, the underlying mechanisms in poplar cuttings remain unclear. In this study, we identified an auxin-mediated regulatory module involved in adventitious root formation in poplar cuttings, comprising a Class C-ARF member, PabARF16, and a non-canonical Aux/IAA member, PabIAA33. The PabIAA33-PabARF16 module positively regulates the expression of PabWOX13 by binding to a variant AuxRE element within its promoter region. Compared with the WT lines, overexpression of PabWOX13 leads to earlier and more root primordium at the bases of poplar cuttings. Additionally, we found that auxin can enhance the formation of adventitious roots in PabWOX13-OE cuttings by elevating the expression of genes related to xylan biosynthesis. These findings provide a genetic strategy for promoting adventitious root formation in poplar vegetative propagation, targeted at enhancing productivity and environmental resilience.