Integrated Proteomics and Metabolomics Analysis Reveals Regulatory Mechanisms Underlying Flower Bud Development in...

Camellia drupifera is an economically important woody oil plant rich in edible seed oil. High-quality and well-developed floral buds are key determinants of its yield. However, studies on the regulatory mechanisms underlying its floral bud development remain relatively limited. In this study, proteomics and metabolomics profiles, along with physiological traits, tested during the final three developmental stages of floral buds. The results showed that the contents of indole-3-acetic acid (IAA), abscisic acid (ABA), and 1-aminocyclopropane-1-carboxylic acid (ACC, a precursor of ethylene) decreased significantly in the second (GZII) and third (GZIII) stages. Gibberellin 3 (GA3) maintained a relatively stable content in GZII with a slight decrease, but decreased significantly in GZIII. These changes in hormone contents may promote the growth of stamens and pistils. During the transition among the three floral bud developmental stages, the relative water content, superoxide dismutase (SOD) activity, soluble sugar content, and soluble protein content decreased significantly, accompanied by an increase in hydrogen peroxide (H₂O₂) content. Integration of differentially accumulated metabolites (DAMs) and differentially expressed proteins (DEPs) analysis showed that the upregulated proteins in the energy metabolism pathway, including pyruvate kinase (PK), citrate synthase (CS), succinate dehydrogenase (SDH), aldolase (ALDO), and hexokinase (HK), promoted the production of adenosine triphosphate (ATP)-a critical energy source for the entire floral development process, including plant hormone synthesis. The decreased IAA content might be attributed to the downregulation of enzymes involved in tryptophan metabolism, such as aldehyde dehydrogenase (ALDH), 3-dehydroquinate dehydratase/shikimate dehydrogenase (aroDE), and chorismate mutase/prephenate dehydratase (aroH). The contents of ABA and GA3 were affected by the downregulation of 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (ispH). Furthermore, the contents of anthocyanins (antioxidant metabolites) decreased significantly in GZII and GZIII, which was caused by the downregulation of key enzymes in the anthocyanin synthesis pathway, including 4-coumarate-CoA ligase (4CL), flavonoid 3'-hydroxylase (F3'H), flavanone 3-hydroxylase (F3H), flavonol synthase (FLS), and anthocyanidin synthase (ANS). This study provides a foundation for further investigating the regulatory metabolites and enzymes involved in C. drupifera floral bud development, and lays a theoretical basis for solving the problem of flower abscission in C. drupifera.