Decoding PHR-Orchestrated Stress Adaptation: A Genome-Wide Integrative Analysis of Transcriptional Regulation Under Abiotic Stress in Eucalyptus grandis

The phosphate starvation response (PHR) transcription factor family play central regulatory roles in nutrient signaling, but its relationship with other abiotic stress remains elusive. In the woody plant <i>Eucalyptus grandis</i>, we characterized 12 EgPHRs, which were phylogenetically divided into three groups, with group I exhibiting conserved structural features (e.g., unique motif composition and exon number). Notably, a protein-protein interaction network analysis revealed that EgPHR had a species-specific protein-protein interaction network: EgPHR6 interacted with SPX proteins of multiple species, while <i>Eucalyptus</i> and poplar PHR uniquely bound to TRARAC-kinesin ATPase, suggesting functional differences between woody and herbaceous plants. A promoter sequence analysis revealed a regulatory network of 59 transcription factors (TFs, e.g., BPC, MYBs, ERFs and WUS), mainly associated with tissue differentiation, abiotic stress, and hormonal responses that regulated <i>EgPHRs'</i> expression. Transcriptomics and RT-qPCR gene expression analyses showed that all <i>EgPHRs</i> dynamically responded to phosphate (Pi) starvation, with the expression of <i>EgPHR2</i> and <i>EgPHR6</i> exhibiting sustained induction, and were also regulated by salt, cold, jasmonic acid, and boron deficiency. Strikingly, nitrogen starvation suppressed most <i>EgPHRs</i>, highlighting crosstalk between nutrient signaling pathways. These findings revealed the multifaceted regulatory role of <i>EgPHRs</i> in adaptation to abiotic stresses and provided insights into their unique evolutionary and functional characteristics in woody plants.