The AP2/ERF Gene Family in Camphor Tree: Structure, Evolution, and Transcriptional Response to Epicoccum Infection

The AP2/ERF transcription factor family plays pivotal roles in plant growth, stress responses, and defense mechanisms, yet its diversity in camphor trees remains underexplored. This study identified 154 AP2/ERF genes in the Camphora officinarum genome, with over 80% belonging to the ERF subfamily, a distribution consistent with other angiosperms. Synteny analysis revealed that tandem and segmental duplications were key drivers of family expansion, suggesting adaptive diversification under ecological pressures. Structural analysis showed that the majority of ERF/RAV subfamily genes possess a single-exon structure, whereas AP2 subfamily genes display muti-exon structures, indicating divergent evolutionary trajectories and potential functional versatility via alternative splicing. Promoter analyses detected numerous hormone- and stress-responsive elements, linking these genes to abscisic acid, auxin, gibberellin signaling, and pathogen defense. Further expression profiling during stem development showed that approximately 60% of CoAP2/ERF genes were constitutively expressed across 17 expression trends, suggesting roles in basal development and stage-specific processes (e.g., lignification). Under Epicoccum poaceicola infection, 23 CoAP2/ERF genes were differentially expressed. Among them, upregulated ERF homologs related to RAP2.2/2.3 suggested roles in hypoxia and antimicrobial responses, while downregulation of ERF5 homologs indicated a growth-defense trade-off, whereby developmental processes are suppressed to prioritize pathogen resistance. Overall, this study deciphers the genomic architecture and structural diversity of CoAP2/ERF genes, along with expression dynamics of these genes in development and biotic stress adaptation of camphor trees. These findings provide critical insights into transcriptional regulation of development and stress responses in camphor trees and establish a theoretical basis for molecular breeding and biotechnological strategies aimed at improving stress resilience in woody plants.