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.

Identification of natural allelic variation in TTL1 controlling thermotolerance and grain size by a rice super pan-genome∞

Continuously increasing global temperatures present great challenges to food security.Grain size,one of the critical components determining grain yield in rice(Oryza sativa L.),is a prime target for genetic breeding.Thus,there is an immediate need for genetic improvement in rice to maintain grain yield under heat stress.However,quantitative trait loci(QTLs)endowing heat stress tolerance and grain size in rice are extremely rare.Here,we identified a novel negative regulator with pleiotropic effects,Thermo‐Tolerance and grain Length 1(TTL1),from the super pan‐genomic and transcriptomic data.Loss‐of‐function mutations in TTL1 enhanced heat tolerance,and caused an increase in grain size by coordinating cell expansion and proliferation.TTL1 was shown to function as a transcriptional regulator and localized to the nucleus and cell membrane.Furthermore,haplotype analysis showed that hapL and hapS of TTL1 were obviously correlated with variations of thermotolerance and grain size in a core collection of cultivars.Genome evolution analysis of available rice germplasms suggested that TTL1 was selected during domestication of the indica and japonica rice subspecies,but still had much breeding potential for increasing grain length and thermotolerance.These findings provide insights into TTL1 as a novel potential target for the development of high‐yield and thermotolerant rice varieties.

A domesticated Harbinger transposase forms a complex with HDA6 and promotes histone H3 deacetylation at genes but not TEs in Arabidopsis

In eukaryotes,histone acetylation is a major modification on histone N-terminal tails that is tightly connected to transcriptional activation.HDA6 is a histone deacetylase involved in the transcriptional regulation of genes and transposable elements(TEs)in Arabidopsis thaliana.HDA6 has been shown to participate in several complexes in plants,including a conserved SIN3 complex.Here,we uncover a novel protein complex containing HDA6,several Harbinger transposon-derived proteins(HHP1,SANT1,SANT2,SANT3,and SANT4),and MBD domain-containing proteins(MBD1,MBD2,and MBD4).We show that mutations of all four SANT genes in the sant-null mutant cause increased expression of the flowering repressors FLC,MAF4,and MAF5,resulting in a late flowering phenotype.Transcriptome deep sequencing reveals that while the SANT proteins and HDA6 regulate the expression of largely overlapping sets of genes,TE silencing is unaffected in sant-null mutants.Our global histone H3 acetylation profiling shows that SANT proteins and HDA6 modulate gene expression through deacetylation.Collectively,our findings suggest that Harbinger transposon-derived SANT domain-containing proteins are required for histone deacetylation and flowering time control in plants.