JA-mediated MYC2/LOX/AOS feedback loop regulates osmotic stress response in tea plant

Osmotic stress caused by low-temperature,drought and salinity was a prevalent abiotic stress in plant that severely inhibited plant development and agricultural yield,particularly in tea plant.Jasmonic acid(JA)is an important phytohormone involving in plant stress.However,underlying molecular mechanisms of JA modulated osmotic stress response remains unclear.In this study,high concentration of mannitol induced JA accumulation and increase of peroxidase activity in tea plant.Integrated transcriptome mined a JA signaling master,MYC2 transcription factor is shown as a hub regulator that induced by mannitol,expression of which positively correlated with JA biosynthetic genes(LOX and AOS)and peroxidase genes(PER).CsMYC2 was determined as a nuclei-localized transcription activator,furthermore,ProteinDNA interaction analysis indicated that CsMYC2 was positive regulator that activated the transcription of CsLOX7,CsAOS2,CsPER1 and CsPER3via bound with their promoters,respectively.Suppression of CsMYC2 expression resulted in a reduced JA content and peroxidase activity and osmotic stress tolerance of tea plant.Overexpression of CsMYC2 in Arabidopsis improved JA content,peroxidase activity and plants tolerance against mannitol stress.Together,we proposed a positive feedback loop mediated by CsMYC2,CsLOX7 and CsAOS2 which constituted to increase the tolerance of osmotic stress through fine-tuning the accumulation of JA levels and increase of POD activity in tea plant.

Duplication and transcriptional divergence of three Kunitz protease inhibitor genes that modulate insect and pathogen defenses in tea plant(Camellia sinensis)

Kunitz protease inhibitors(KPIs)are ubiquitous in plants and act as crucial compounds in defense responses against insect attack and pathogen infection.However,the influence of gene duplication on the postdivergence of the CsKPI genes involved in biotic stresses in tea plant is not well known.Here,we identified three CsKPI genes from tea plant(Camellia sinensis)and characterized their expression and evolutionary patterns among plant species.We found that CsKPI1,CsKPI2,and CsKPI3 diverged from their common ancestor 72.94 million years ago(MYA),and the tandem duplication of CsKPI2 and CsKPI3 occurred 26.78 MYA.An in vitro protein assay showed that the three CsKPI proteins were functional and inhibited the production of p-nitroanilide(PNA)from an artificial substrate.The three CsKPI-GFP fusion proteins localized to the cytoplasm.We showed that salicylic acid(SA)and transcripts of CsKPI2 and CsKPI3 significantly accumulated after infection with Glomerella cingulata.The application of exogenous SA stimulated the high expression of both CsKPI2 and CsKPI3 by activating cis-elements within their promoters.Under Ectropis oblique attack,CsKPI1 expression and jasmonic acid(JA)levels were more abundant in both insect-damaged leaf tissues and undamaged neighboring leaves.The application of jasmonic acid methyl ester elicited high expression levels of CsKPI1,suggesting that CsKPI1 accumulation requires JA production in tea plant.The overall findings suggest that the transcriptional divergence of KPI genes after duplication led to the specialized role of CsKPI1 in the physiological response to insect stress;the functional conservation between CsKPI2 and CsKPI3 confers resistance to pathogen infection in tea plant.

栽培茶树的驯化起源与传播

茶作为世界上最重要的饮品之一,其栽培类型的驯化起源一直是人们关注的热点。本文总结了近年相关研究的进展,讨论了存在的问题,并对未来的研究方向提出建议。长江流域及以南地区分布有众多栽培茶树的野生近缘种,特别集中于云南、贵州、广西等地;一方面南方各族语言中"茶"发音的相似,暗示了茶知识起源的单一性,最可能起源于古代的巴蜀或云南,另一方面遗传分析揭示栽培的茶存在多个起源中心,即使Camellia sinensis(L.)O.Kuntze的几个栽培变种也可能起源于不同的地区;文献记载,茶的栽培中心曾经从西向东再向南迁移,遗传多样性的变化也揭示了这一可能性,但考古发现却提示最早的栽培茶可能出现在长江流域的最东部。我们推测在茶知识及栽培品种的传播过程中,各地野生近缘植物的基因渗入栽培类型中,或各地居民直接用当地野生茶培育出新的栽培茶类型,从而导致遗传上的复杂性和语言上的一致性并存。茶树的祖先类型、起源地点、起源时间以及栽培品种的演变历程都还需要更为明确的证据,未来应该以整个茶组植物为对象,将茶文化、群体遗传学、谱系地理、人类学、气候变化、考古等多学科研究进行整合分析。

The Reference Genome of Tea Plant and Resequencing of 81 Diverse Accessions Provide Insights into Its Genome Evolution and Adaptation

Tea plant is an important economic crop,which is used to produce the world's oldest and most widely consumed tea beverages.Here,we present a high-quality reference genome assembly of the tea plant(Camellia sinensis var.sinensis)consisting of 15 pseudo-chromosomes.LTR retrotransposons(LTR-RTs)account for 70.38%of the genome,and we present evidence that LTR-RTS play critical roles in genome size expansion and the transcriptional diversification of tea plant genes through preferential insertion in promoter regions and introns.Genes,particularly those coding for terpene biosynthesis pro-teins,associated with tea aroma and stress resistance were significantly amplified through recent tandem duplications and exist as gene clusters in tea plant genome.Phylogenetic analysis of the sequences of 81 tea plant accessions with diverse origins revealed three well-differentiated tea plant populations,support-ing the proposition for the southwest origin of the Chinese cultivated tea plant and its later spread to western Asia through introduction.Domestication and modern breeding left significant signatures on hundreds of genes in the tea plant genome,particularly those associated with tea quality and stress resis-tance.The genomic sequences of the reported reference and resequenced tea plant accessions provide valuable resources for future functional genomics study and molecular breeding of improved cul-tivars of tea plants.