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.

Low temperature is a major stress that severely affects tree growth and development. Despite the fact that the molecular mechanisms behind cold tolerance and associated regulatory networks in these trees remain largely unexplored, we conducted a study to examine the overall changes in metabolites and regulatory pathways of Populus ussuriensis kom. when exposed to cold stress, utilizing a comprehensive multi-omics approach. Transcriptomes exposed to cold stress reveal that most of the candidate genes related to the Calvin–Benson–Bassham cycle and flavonoid synthesis were upregulated. Joint analysis revealed that within 6–48 h of low-temperature treatment, differential genes (such as PAL and CHS) in the flavonoid biosynthesis pathway and metabolites (such as quercetin) were significantly upregulated, indicating a positive correlation under short-term stress. However, prolonged treatment (72 h) may trigger metabolic feedback, leading to a decrease in flavonoid content. In addition, the measurements of gas exchange and metabolite assays of P. ussuriensis showed that photosynthetic acclimation led to a change in the sugar accumulation and starch degradation in response to low temperature, indicating that extensive changes occurred due to the cold and improved tolerance in P. ussuriensis. This study provides a new basis for future studies on the molecular mechanism of cold tolerance at the transcriptional and metabolic levels.

Drought stress significantly impairs plant growth and productivity, which triggers complex adaptive responses mediated by diverse gene families. Among these, the TOPLESS (TPL)/TPL-related (TPR) family of transcriptional corepressors plays a crucial role by recruiting epigenetic modifiers through interactions with EAR motif-containing proteins. However, genome-wide studies of this corepressor family and its associated regulatory networks with EAR motif-containing repressors remain limited. This study aimed to characterize the TPL/TPR transcriptional corepressor family in Populus ussuriensis Kom., elucidate their regulatory networks with EAR motif-containing repressors, and validate their functional roles in drought stress adaptation. To this end, we identified 21 TPL/TPR genes in P. ussuriensis (PuTPLs), classified them into five subfamilies, and found they are evolutionarily conserved with Arabidopsis thaliana and Populus trichocarpa, harboring characteristic CTLH and WD40 domains. Given that TPL/TPR proteins are recruited by transcription factors containing repression motifs, we constructed a putative TPL/TPR-EAR motif interaction network representing a core paradigm of negative regulation. Expression profiling under drought stress showed significant upregulation of most PuTPLs in a tissue-specific and temporal manner. Functional validation using transgenic P. ussuriensis lines overexpressing five PuTPLs demonstrated enhanced drought tolerance, evidenced by reduced electrolyte leakage and malondialdehyde content and increased proline accumulation. Our study provides the first comprehensive genome-wide analysis of the TPL/TPR family in P. ussuriensis, establishes a core EAR-mediated negative regulatory network, and validates the critical role of these genes in drought stress adaptation, providing valuable resources for future mechanistic research and breeding of stress-resistant trees.