MiRNA-target pairs regulate adventitious rooting in Populus: a functional role for miR167a and its target Auxin response factor 8

The ability of a plant to form roots from its non-root tissues is ecologically advantageous during rapid adaptation to a changing environment. Although this biological phenomenon has been widely utilized for cuttings in many economically important agronomic and tree species, its genetic and developmental mechanisms have been poorly understood. In this study, we conducted an association analysis of small RNAs, the degradome and the transcriptome of adventitious rooting in poplar softwood cuttings, which revealed that 373 miRNA-target pairs were detected. Of these, 72 significantly differentially expressed targets were screened as likely to modulate adventitious root (AR) development, in conjunction with plant hormone signal transduction. Poplar miR167a and its targets PeARF6s and PeARF8s were subjected to functional verification of their ability to mediate plant growth and hormone signal transduction. Overexpression of miR167a inhibited target transcripts and improved lateral root (LR) development in poplar, while overexpressing PeARF8.1(mut) increased AR numbers and slightly inhibited LR development. Taken together, these results suggest that miR167a-PeARF8.1 modules play crucial roles in regulating AR and LR development in poplar and improve the adaptation of poplar to more complex environments.