Transcriptome analysis reveals seasonal dynamics and oil yield associated regulatory networks in Camphora longepaniculata

Camphora longepaniculata is a terpene-rich aromatic tree valued for its cineole-dominant essential oils, but the molecular basis of its seasonal dynamics and variation in oil yield remains unclear. Here, we profiled leaf transcriptomes from high, medium, and low oil lines collected across four seasons and used a multifactor framework to separate the effects of season, oil type, and their interaction on gene expression. High-quality RNA-seq data were obtained from 34 libraries. Global transcriptome analyses showed that season was the primary source of expression variation, whereas oil-yield class contributed a stable but secondary component to transcriptional divergence. Differential expression analysis indicated that differences among oil-yield types were most pronounced in autumn and winter, particularly between the low-oil line and the high- and medium-oil lines, while seasonal transcriptional changes varied among chemotypes. Main-effect analysis identified large sets of genes associated with season and oil type. Clustering of season-responsive genes resolved seven temporal expression modules, including winter-induced, autumn-biased, summer-activated, and spring-preferential patterns, indicating extensive transcriptome reprogramming over the annual cycle. In parallel, oil-type-responsive genes clearly distinguished the low-oil materials from high- and medium-oil materials, supporting a stable transcriptional program linked to oil accumulation. Weighted gene co-expression network analysis identified a trait-associated module that was positively correlated with high oil content and enriched for signaling, membrane-associated, and regulatory functions. Hub candidate genes in this module included ABC transporters, O-methyltransferases, cytochrome P450s, UDP-glycosyltransferases, and a terpene synthase. Consistent with these patterns, multiple genes in the MVA and MEP pathways showed higher expression in the high-oil line, suggesting a possible association with terpene precursor supply. Together, these results indicate that essential-oil accumulation in C. longepaniculata is associated with a stable oil-type-related transcriptional program overlaid with strong seasonal reprogramming, and they provide candidate genes and regulatory modules for future functional studies and molecular breeding of high-oil germplasm.