Abstract
The formation of plant flower buds is regulated by various genes occurring upstream in floral induction pathways. However, the precise regulatory roles and underlying molecular mechanisms of these pathways in Camellia flower bud formation remain unclear. This study investigated the annual periodicity pattern of flower bud formation in two Camellia species exhibiting distinct flowering phenotypes: Camellia azalea, which initiates flower buds continuously throughout the year, and Camellia japonica, which forms buds only between May and July. C. azalea helps address the lack of summer-flowering representatives within the Camellia genus. Elucidating its unique molecular mechanism of flowering regulation provides valuable guidance for breeding new cultivars with summer blooming traits. Comparative transcriptome analysis of mature leaves sampled annually from the two Camellia species revealed the highest number of differentially expressed genes (DEGs) in C. azalea between May and December, whereas in C. japonica, the peak number of DEGs occurred between June and December. Gene ontology analysis indicated that the most enriched category in the transcriptomes of both species was oxidoreductase activity, which was followed by cofactor binding in C. azalea, whereas in C. japonica, it was cellular amino acid metabolic process. Flowering-related genes were identified from the transcriptome database, yielding 248 transcripts in C. azalea and 257 in C. japonica. The transcriptome analysis also revealed that C. azalea lacks certain floral inhibitory pathways that are present in C. japonica, such as the photoperiod pathway genes including GI2, FKF1, and COL14 and the thermosensitive pathway gene SVP. The reliability of the transcriptome results was further validated by quantitative real-time PCR (qRT-PCR) analysis. These results suggest that differences in upstream regulatory mechanisms within the floral induction pathways of C. azalea and C. japonica may underlie the species-specific patterns in the annual distribution of flower bud formation.