PuUBL5-mediated ZINC FINGER PROTEIN 1 stability is critical for root development under drought stress in Populus ussuriensis

Abstract C2H2-type zinc finger protein (ZFP) transcription factors influence root growth and development. However, their potential roles in inhibiting adventitious root (AR) and lateral root (LR) formation in trees remain unclear. Here, we report that the ABA-responsive C2H2-type zinc finger protein transcription factor (PuZFP1) regulates Populus ussuriensis root development to enhance drought tolerance. PuZFP1 negatively regulates LR development by binding to the PuWRKY46 promoter and inhibiting its expression. At the same time, PuZFP1 promotes AR elongation by repressing Clade E Growth-Regulating (EGR) Type 2C protein phosphatases (PuEGR1). In PuZFP1-overexpressing lines, a higher ABA/IAA ratio in the differentiated zone (DZ) drives PuWRKY46-mediated LR inhibition. Conversely, a lower ABA/IAA ratio is associated with AR elongation and the expression of the downstream target gene PuEGR1 in the elongation zone (EZ). Notably, PuZFP1 physically interacts with Ubiquitin-like protein 5 (PuUBL5) and undergoes 26S proteasome-mediated degradation. Taken together, our findings shed light on the role of the PuUBL5–PuZFP1 module in mediating the crosstalk between LR emergence and AR elongation via ABA/auxin signaling in drought-stressed P. ussuriensis, and provide insights into the regulatory network underlying PuZFP1-mediated root growth in poplar.