The high-resolution three-dimensional(3D)chromatin map of the tea plant(Camellia sinensis)

Dear Editor,Tea plant(Camellia sinensis(L.)O.Kuntze)is one of the world’s most important non-alcoholic beverages,with great economic,health,and cultural value.Recently,several genomes of C.sinensis var.assamica(CSA)(Yunkang 10),C.sinensis var.sinensis(CSS)(Shuchazao,Biyun,Longjing 43,Tieguanyin,Huangdan),and ancient tea plant(DASZ)have been deciphered[1-3].

5mC DNA methylation modification-mediated regulation in tissue functional differentiation and important flavor substance synthesis of tea plant (Camellia sinensis L.)

In plants,5mC DNA methylation is an important and conserved epistatic mark involving genomic stability,gene transcriptional regulation,developmental regulation,abiotic stress response,metabolite synthesis,etc.However,the roles of 5mC DNA methylation modification(5mC methylation)in tea plant growth and development(in pre-harvest processing)and flavor substance synthesis in pre-and post-harvest processing are unknown.We therefore conducted a comprehensive methylation analysis of four key pre-harvest tissues(root,leaf,flower,and fruit)and two processed leaves during oolong tea post-harvest processing.We found that differential 5mC methylation among four key tissues is closely related to tissue functional differentiation and that genes expressed tissue-specifically,responsible for tissue-specific functions,maintain relatively low 5mC methylation levels relative to non-tissue-specifically expressed genes.Importantly,hypomethylation modifications of CsAlaDC and TS/GS genes in roots provided the molecular basis for the dominant synthesis of theanine in roots.In addition,integration of 5mC DNA methylationomics,metabolomics,and transcriptomics of post-harvest leaves revealed that content changes in flavor metabolites during oolong tea processing were closely associated with transcription level changes in corresponding metabolite synthesis genes,and changes in transcript levels of these important synthesis genes were strictly regulated by 5mC methylation.We further report that some key genes during processing are regulated by 5mC methylation,which can effectively explain the content changes of important aroma metabolites,includingα-farnesene,nerolidol,lipids,and taste substances such as catechins.Our results not only highlight the key roles of 5mC methylation in important flavor substance synthesis in pre-and post-harvest processing,but also provide epimutation-related gene targets for future improvement of tea quality or breeding of whole-tissue high-theanine varieties.

Combined metabolic phenotypes and gene expression profiles revealed the formation of terpene and ester volatiles during white tea withering process

Withering is a critical process to form the unique aroma of high-quality white tea.To study the mechanism underlying aroma changes during the white withering,we herein conducted volatile metabolomics and transcriptomics of the young leaves from the'Fuding Dahaocha'tea cultivar.As the withering time extended,the content of major aroma components increased significantly,score of sensory evaluation and Owuor's flavor index(OFI)also increased.The aromatic substances that accumulated during white tea withering were mainly volatile terpenes and esters.Their change trends were largely consistent with the gene expression of theα-linolenic acid metabolic pathways,while the correlation between the trends in volatiles and the gene expression of the terpenoid biosynthesis pathways was more complex and induced by the jasmonic acid(JA)signaling pathway.Additionally,we also explored the regulation pattern of key genes in the signaling pathway by related transcription factors.Three coexpression networks strongly correlated to the variation of volatile component content during withering were identified by weighted gene coexpression network analysis(WGCNA).Our results provide a new perspective on the processing mechanism and quality improvement of white tea.

Recent Advances in Assembly of Complex Plant Genomes

Over the past 20 years,tremendous advances in sequencing technologies and computational algorithms have spurred plant genomic research into a thriving era with hundreds of genomes decoded already,ranging from those of nonvascular plants to those of flowering plants.However,complex plant genome assembly is still challenging and remains difficult to fully resolve with conventional sequencing and assembly methods due to high heterozygosity,highly repetitive sequences,or high ploidy characteristics of complex genomes.Herein,we summarize the challenges of and advances in complex plant genome assembly,including feasible experimental strategies,upgrades to sequencing technology,existing assembly methods,and different phasing algorithms.Moreover,we list actual cases of complex genome projects for readers to refer to and draw upon to solve future problems related to complex genomes.Finally,we expect that the accurate,gapless,telomere-totelomere,and fully phased assembly of complex plant genomes could soon become routine.