Characterization, stress responses and protein-protein interactions of the Paulownia BBX transcription factor

The BBX transcription factor family plays a crucial role in light-mediated growth and development, including seed germination, photomorphogenesis, and stress responses. This study identified 37 PfBBX proteins in the Paulownia genome, classified into five subfamilies. We analyzed the bioinformatics characteristics and expression patterns of these proteins under drought and high salt stress. The PfBBX transcription factor family includes 34 acidic proteins, 37 hydrophilic proteins, and 26 nucleoproteins. This gene family is distributed across 16 chromosomes. The promoter regions contain 40 cis-acting elements, including light-responsive and stress-responsive elements. Transcriptome analysis revealed that 11 PfBBX genes, including PfBBX1 , respond to drought stress. Additionally, 9 genes, including PfBBX18, respond to salt stress. Notably, PfBBX13 and PfBBX14 exhibit dual responsiveness to drought and salt stress, highlighting their critical roles in abiotic stress adaptation. In addition to drought and salt stress, 17 PfBBX genes, including PfBBX1 , respond to phytoplasma stress. Yeast two-hybrid analysis demonstrated that PfBBX2, PfBBX17, PfBBX20, and PfBBX33 exhibit transcriptional activation activity. Furthermore, PfBBX2, PfBBX20, and PfBBX17 interact with PfHY5–2, while PfBBX20 and PfBBX2 interact with PfHY5–1. PfBBX29 forms heterodimers with PfBBX17, PfBBX2, and PfBBX33, with hydrogen bonding being the primary interaction mechanism. This study provides a foundation for understanding the biological functions of PfBBX genes in Paulownia and offers insights for developing stress-resistant tree species and promoting sustainable forestry. • Study identified 37 BBX proteins in Paulownia , grouped into five subfamilies, including 34 acidic, 37 hydrophilic, and 26 nucleoproteins. • Transcriptome analysis showed 11 PfBBX genes respond to drought, 9 to salt stress, and 17 to phytoplasma, with PfBBX13 and PfBBX14 responsive to both drought and salt. • PfBBX proteins form heterodimers via hydrogen bonds, with PfBBX29 specifically interacting with PfBBX17, PfBBX2, and PfBBX33.