Supernumerary (B) chromosomes are widespread in numerous plants, including the Lilium genus. However, their origin remains unclear. This study used traditional and modern cytogenetics to analyze the triploid lily cultivar ‘Eyeliner’ (LAA) to identify the microsporogenesis, fertility, and chromosome composition of its progeny and record a case of potential B chromosome formation. The results indicated anomalous meiosis of LAA in all processes. In microspores, different cells had different numbers of chromosomes and fragments. Moreover, the fluorescence in situ hybridization (FISH) results showed that some fragments contained telomere signals at both ends. The LAA × AA progenies were aneuploid, with one progeny containing a small aberrant chromosome (potential B chromosome). The genomic in situ hybridization (GISH) results showed that the aberrant chromosome originated from the L genome. In contrast, the FISH results showed that the aberrant chromosome contained two telomere signals. This suggests that the anomalous meiosis of the triploid lily forms chromosome bridges, fragments, and small aberrant chromosomes (isochromosome), which eventually form aneuploid gametes containing small aberrant chromosomes passed on to the progeny. This study provides a case in which the potential B chromosomes are derived from the A chromosomes.

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.