Differential accumulation mechanisms of purine alkaloids and catechins in Camellia ptilophylla,a natural theobromine-rich tea

Tea is consumed worldwide due to its charming flavor and the refreshing effects conferred by caffeine.Caffeine however has undesirable side effects,such as sleep disturbance.Camellia ptilophylla is known for its low caffeine content,and the biosynthesis of purine alkaloids in this species has become a hot topic.In this study,the accumulation of purine alkaloids in a natural C.ptilophylla population(32 plants)was analyzed,and the results showed that 81.25%of this population were caffeine-free,containing only theobromine(TB),while six plants contained both theobromine and caffeine(CAF).RNA-seq analysis of two C.ptilophylla plants with contrasting purine alkaloid contents(TB and CAF)revealed that xanthosine synthesis genes of the SAM cycle and AMP pathway were significantly related to the differential accumulation of purine alkaloids between TB and CAF.The high theobromine content in TB was attributed to the significantly higher expression of TCS-2,TCS-3 and MXMTs and downregulation of the xanthosine degradation pathway in comparison to CAF.Additionally,CsMYB184 was significantly upregulated in TB,opposing the expression pattern of TCS1,but consistent with that of other TCSs and MXMTs.Furthermore,the upregulated expression of catechin biosynthesis genes,F3'H,F3'5'H and SCPLs in TB corresponded to a higher gallocatechin gallate(GCG)content.Overall,these findings provide new insights into the accumulation of theobromine and GCG,which may facilitate the development of tea plant cultivars with low-caffeine or high GCG to meet the diverse demands of consumers.

Coexpression network analysis reveals an MYB transcriptional activator involved in capsaicinoid biosynthesis in hot peppers

Plant biosynthesis involves numerous specialized metabolites with diverse chemical natures and biological activities.The biosynthesis of metabolites often exclusively occurs in response to tissue-specific combinatorial developmental cues that are controlled at the transcriptional level.Capsaicinoids are a group of specialized metabolites that confer a pungent flavor to pepper fruits.Capsaicinoid biosynthesis occurs in the fruit placenta and combines its developmental cues.Although the capsaicinoid biosynthetic pathway has been largely characterized,the regulatory mechanisms that control capsaicinoid metabolism have not been fully elucidated.In this study,we combined fruit placenta transcriptome data with weighted gene coexpression network analysis(WGCNA)to generate coexpression networks.A capsaicinoid-related gene module was identified in which the MYB transcription factor CaMYB48 plays a critical role in regulating capsaicinoid in pepper.Capsaicinoid biosynthetic gene(CBG)and CaMYB48 expression primarily occurs in the placenta and is consistent with capsaicinoid biosynthesis.CaMYB48 encodes a nucleus-localized protein that primarily functions as a transcriptional activator through its C-terminal activation motif.CaMYB48 regulates capsaicinoid biosynthesis by directly regulating the expression of CBGs,including AT3a and KasIa.Taken together,the results of this study indicate ways to generate robust networks optimized for the mining of CBG-related regulators,establishing a foundation for future research elucidating capsaicinoid regulation.