Flavonoids are the main medicinal ingredients in Camellia nitidissima, but the regulatory mechanism of flavonoid biosynthesis in flowers is unclear; therefore, the flavonoids in C. nitidissima have not been effectively used. The present study performed full-length transcriptome sequencing of C. nitidissima flower. Furthermore, the reported RNA-sequencing data of C. nitidissima petals were reanalyzed using the full-length transcriptome as a reference, and the regulatory mechanism of flavonoid synthesis in petals was elucidated. The analysis identified 43,350 isoforms annotated in non-redundant protein (Nr), Kyoto Encyclopedia of Genes and Genomes (KEGG), EuKaryotic Orthologous Groups (KOG), and Swiss-Prot databases, among which 34,602 aligned to Camellia sinensis genes. A total of 11,857 differentially expressed genes (DEGs), including 112 related to flavonoid synthesis, were identified by pairwise comparison. Subsequently, analysis of the phylogeny and the conserved motifs of R2R3-MYB using the proteins sequences identified three R2R3-MYB transcription factors that regulated flavonoid biosynthesis. Weighted gene co-expression network analysis (WGCNA) identified phenylalanine ammonia-lyase (PAL) and 4-coumarate: CoA ligase(4CL) as the hub genes and showed that bHLH79 interacted with PAL. Finally, validated the expression of seven DEGs involved in flavonoid biosynthesis using real-time quantitative PCR (qRT-PCR). Thus, the present study generated and used the full-length transcriptome as the reference to analyze the transcriptome of petals and proposed a possible regulatory mechanism of flavonoid synthesis in C. nitidissima. The study's findings unravel the genetic mechanisms underlying flavonoid synthesis and suggest candidate genes for the genetic improvement of C. nitidissima.

The mitochondrial genome of Camellia nitidissima was sequenced by Illumina and Pacbio sequencing. The results of sequences showed that a total length was 949,915 bp, and the GC content was 45.7% in assembled mitochondrial genome of C. nitidissima. 71 unigenes had been found, including 36 coding proteins and 35 non-coding proteins. Subsequently, the phylogenetic tree was built on 24 plants with the maximum-likelihood method, which had high bootstrap value and fited to the angiosperm phylogeny group classification (APG IV). The study's findings unravel the taxonomic status of C. nitidissima and benefit the evolution study.

Camellia nitidissima Chi is a popular ornamental plant because of its golden flowers, which contain flavonoids and carotenoids. To understand the regulatory mechanism of golden color formation, the metabolites of C. nitidissima petals at five different developmental stages were detected, a proteome map of petals was first constructed via tandem mass tag (TMT) analysis, and the accuracy of the sequencing data was validated via parallel reaction monitoring (PRM). Nineteen color components were detected, and most of these components were carotenoids that gradually accumulated, while some metabolites were flavonoids that were gradually depleted. A total of 97,647 spectra were obtained, and 6,789 quantifiable proteins were identified. Then, 1,319 differentially expressed proteins (DEPs) were found, 55 of which belong to the flavonoid and carotenoid pathways, as revealed by pairwise comparisons of protein expression levels across the five developmental stages. Notably, most DEPs involved in the synthesis of flavonoids, such as phenylalanine ammonium lyase and 4-coumarate-CoA ligase, were downregulated during petal development, whereas DEPs involved in carotenoid synthesis, such as phytoene synthase, 1-deoxy-D-xylulose-5-phosphate synthase, and β-cyclase, tended to be upregulated. Furthermore, protein‒protein interaction (PPI) network analysis revealed that these 55 DEPs formed two distinct PPI networks closely tied to the flavonoid and carotenoid synthesis pathways. Phytoene synthase and chalcone synthase exhibited extensive interactions with numerous other proteins and displayed high connectivity within the PPI networks, suggesting their pivotal biological functions in flavonoid and carotenoid biosynthesis. Proteomic data on the flavonoid and carotenoid biosynthesis pathways were obtained, and the regulatory roles of the DEPs were analyzed, which provided a theoretical basis for further understanding the golden color formation mechanism of C. nitidissima. The online version contains supplementary material available at 10.1186/s12870-024-05737-7.

Background: PAL genes are crucial for plant growth and stress response, yet studies on the PAL gene family in Camellia nitidissima are sparse. Methods: The PAL gene family was screened from the entire genome of C. nitidissima, and their physicochemical properties, chromosomal locations, intraspecific and interspecific collinearity, conserved motifs, phylogenetic trees, cis-acting elements, and gene structures were analyzed. The expression patterns of the CnPAL genes were compared across different tissues, and the highly expressed CnPAL1 gene was expressed in prokaryotes, and its enzyme activity was validated using UPLC-MS technology. Results: The results revealed that six CnPALs were identified in the C. nitidissima genome, distributed unevenly across six chromosomes. The CnPAL proteins shared similar physicochemical properties, with highly conserved motifs and gene structures. Promoter analysis showed multiple cis-acting elements in the CnPALs genes. Intra-species collinearity analysis revealed that all CnPALs were collinear with multiple PAL genes in C. nitidissima, while inter-species collinearity analysis indicated that CnPALs were collinear with the PAL genes in Camellia oleifera and Camellia sinensis. Furthermore, the transcriptomic data of C. nitidissima demonstrated tissue-specific expression of the CnPALs, although qRT-PCR validation showed some discrepancies with the sequencing result. The qRT-PCR revealed varied expression patterns among the six CnPALs, with the CnPAL1 gene showing relatively higher expression levels. Subsequently, cloning, prokaryotic expression, and enzyme activity analysis confirmed the effective catalytic activity of the CnPAL1 protein. Conclusions: This study lays the foundation for understanding the functions of CnPAL genes and offers insights for genetic improvement of C. nitidissima.