Reference-guided transcriptomics resolves CoHMGR family composition and expression diversification during postharvest...

Camellia oleifera is an important woody oil crop whose seed kernels contain squalene and other bioactive oil constituents. Although short-term postharvest conditioning is commonly used in oil-tea processing, the molecular behavior of the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) system during this early postharvest window remains poorly characterized. Here, mature C. oleifera seed kernels were subjected to controlled warm conditioning at 35 °C and 95% relative humidity for 12-24 h to characterize HMGR-related biochemical responses, gene-family features, and transcriptomic changes associated with squalene accumulation.

Warm conditioning was associated with a rapid increase in squalene content, rising from 177.58 ± 8.2 µg/g FW at T-0 to 314.30 ± 9.7 µg/g FW at T-12 and remaining elevated at T-24. An ELISA-based estimate of HMGR activity showed a similar early increase. Transcriptome-guided curation resolved five HMGR-related loci, including four canonical CoHMGR genes with conserved class I HMGR-domain support and one truncated HMGR-like locus, LOC_00050219. Integrated phylogenetic, structural, domain-architecture, localization-prediction, and collinearity evidence supported this curated four-member canonical CoHMGR set. Reference-guided RNA-seq and RT-qPCR revealed divergent expression trajectories among canonical members, with HMGR2 showing the strongest warm-conditioning-associated response. NetPhos analysis further prioritized candidate phosphorylation sites in a representative CoHMGR protein, and global transcriptome profiling placed the CoHMGR response within a staged program involving stress signaling, protein homeostasis, and carbon/lipid metabolic reallocation.

This study establishes a reference-guided framework for resolving CoHMGR family composition and interpreting HMGR-associated responses during postharvest warm conditioning in C. oleifera seed kernels. The findings identify prioritized CoHMGR isoforms, candidate phosphorylation sites, and transcriptomic contexts for future protein-level validation and functional studies of postharvest squalene regulation. Importantly, the current evidence supports candidate prioritization rather than direct mechanistic proof, and causal links among candidate kinases or phosphatases, HMGR protein regulation, and squalene biosynthesis remain to be experimentally established.