Identification and Expression Analysis of the SBP Gene Family in Phoebe bournei Under Drought Stress

Phoebe bournei is a rare and economically valuable tree species native to China that plays an important ecological role. In this study, we conducted a genome-wide identification of the SQUAMOSA promoter-binding protein (SBP) transcription factor family in Phoebe bournei and characterized 19 PbSBP genes distributed across 10 chromosomes. Phylogenetic analysis grouped these genes into five distinct subfamilies, each of which showed homology to SBP genes in Arabidopsis thaliana and Oryza sativa, indicating strong evolutionary conservation within the family. All identified PbSBP proteins contain the conserved SBP domain, and some members also harbor additional motifs such as the ANK domain, which may mediate protein–protein interactions. Tissue-specific expression profiling revealed that several PbSBP genes are predominantly expressed in root bark and leaves, suggesting their potential roles in defense responses and developmental regulation. Moreover, qPCR validation showed that PbSBP2, PbSBP9, and PbSBP16 were significantly upregulated under PEG-induced drought stress, implying their involvement in abiotic stress responses. This study provides a foundational understanding of the SBP gene family in P. bournei and highlights candidate genes for future genetic improvement and breeding for stress resistance.