Analysis of Camellia oleifera transcriptome reveals key pathways and hub genes involved during different photoperiods

Camellia oleifera Abel. (C. oleifera) is an important traditional woody species in China that produces edible oil. However, the current literature lacks a proper understanding of C. oleifera's ability to adapt to different photoperiods.Our results indicate that the photoperiod can significantly impact flowering time in C. oleifera. We grew a total of nine samples under the short day condition (SD), middle day condition (MD) and long day condition (LD). Transcriptome analysis yielded 66.94 Gb of high-quality clean reads, with an average of over 6.73 Gb of reads for per sample. Following assembly, a total of 120,080 transcripts were obtained and 94,979 unigenes annotated. A total of 3475 differentially expressed genes (DEGs) were identified between the SD_MD, SD_LD, and MD_LD gene sets. Moreover, WGCNA identified ten gene modules. Genes in pink module (92 genes) were positively correlated with SD, and negatively correlated with both MD and LD. Genes in the magenta module (42 genes) were positively correlated with MD and negatively correlated with both LD and SD. Finally, genes in the yellow module (1758 genes) were positively correlated with both SD and MD, but negatively correlated with LD. KEGG enrichment analysis revealed that genes in the pink, magenta, and yellow modules were involved in flavonoid biosynthesis, amino sugar and nucleotide sugar metabolism and circadian rhythm pathways. Additionally, eight hub genes (GI, AP2, WRKY65, SCR, SHR, PHR1, ERF106, and SCL3) were obtained through network analysis. The hub genes had high connectivity with other photoperiod-sensitive DEGs. The expression levels of hub genes were verified by qRT-PCR analysis.An increase in light duration promotes earlier flowering of C. oleifera. Flavonoid biosynthesis, amino sugar and nucleotide sugar metabolism, and circadian rhythm pathways may function in the photoperiodic flowering pathway of C. oleifera. We also identified eight hub genes that may play a role in this pathway. Ultimately, this work contributes to our understanding of the photoperiodic flowering pathway of C. oleifera and further informs molecular breeding programs on the plant's photoperiodic sensitivity.