Fine-tuning of catechin accumulation by MYB-mediated functionally divergence of CoLARs in Camellia oleifera fruit shells

Camellia oleifera, a leading global woody oil crop with high-value edible seed oil, faces a critical industrial challenge in the efficient utilization of its abundant fruit shell by-products from oil extraction. The objective of this study was to identify key genes and regulatory mechanisms controlling catechin (CAT) accumulation in C. oleifera fruit shells during ripening. Metabolite quantification, transcriptome sequencing, prokaryotic expression, enzymatic assays, yeast one-hybrid and dual-luciferase assays were conducted in this research. This study analyzed the dynamic trends of CAT accumulation and biosynthesis in C. oleifera cv. ‘HuaShuo’ (HS) fruit shells as the fruit matured. Results show that catechin content drops from 77.53 mg/100 g (FW) to 19.63 mg/100 g (FW) from July to September. Three leucoanthocyanidin reductases (CoLAR1, CoLAR2, and CoLAR3) were demonstrated to possess the ability to catalyze CAT production. CoLAR1 exhibited the highest substrate affinity, while CoLAR3 had the highest catalytic efficiency. Additionally, four CoMYB transcription factors were identified as potentially regulating CAT biosynthesis. Functional assays demonstrated that CoMYB4 acted as an activator of CoLAR1/2/3 , whereas CoMYB123 functioned as a repressor. CoMYB5a and CoMYB6 specifically regulated CoLAR2 , thus forming a sophisticated regulatory network. Coordinated downregulation of CoLARs and MYB regulators directly leads to CAT depletion. This study clarifies the regulatory mechanism of CAT metabolism and provides gene targets for high-value utilization of oil-tea fruit shells.