The TIFY gene family is specific to land plants, exerting immense influence on plant growth and development as well as responses to biotic and abiotic stresses. Here, we identify 25 TIFY genes in the poplar (Populus trichocarpa) genome. Phylogenetic tree analysis revealed these PtrTIFY genes were divided into four subfamilies within two groups. Promoter cis-element analysis indicated most PtrTIFY genes possess stress- and phytohormone-related cis-elements. Quantitative real-time reverse transcription polymerase chain reaction (qRT–PCR) analysis showed that PtrTIFY genes displayed different expression patterns in roots under abscisic acid, methyl jasmonate, and salicylic acid treatments, and drought, heat, and cold stresses. The protein interaction network indicated that members of the PtrTIFY family may interact with COI1, MYC2/3, and NINJA. Our results provide important information and new insights into the evolution and functions of TIFY genes in P. trichocarpa.

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.

Calcium ions (Ca²⁺) play a crucial role as a key messenger in various adaptive and developmental processes. In plants, the calcineurin B-like protein (CBL) family is a unique calcium sensor, which plays a key role in regulating plant growth and development as well as responding to external environmental stimuli throughout the Ca²⁺ signaling pathway. However, the CBL gene family in poplar has not been systematically described. In this study, thirteen CBL genes were identified from the Populus trichocarpa genome using bioinformatics methods. Multiple sequence alignment showed that all PtrCBLs contained four conserved EF-hand domains. Promoter cis-acting elements revealed that PtrCBL promoters contained at least one abiotic-related or hormone response element. A protein–protein interaction network revealed that PtrCBLs interacted with various CIPK proteins to participate in growth and development or respond to environmental stimuli in poplar. Transcriptome data demonstrated that numerous PsnCBLs were involved in the response to alkaline stress in Populus simonii × Populus nigra. RT-qPCR and RNA-seq analyses implied that PsnCBLs exhibited complex expression patterns in poplar under alkaline stress at different time points. These results provide comprehensive information for future research on the CBL gene function and lay a research foundation for studying alkaline stress in poplar.