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.

Cytological and transcriptional insights of late-acting selfincompatibility in tea plants(Camellia sinensis)

Self-incompatibility(SI)is a kind of plant fertilization obstacle,which can prevent the harmful effects of inbreeding decline,but it hinders the breeding of inbred lines.Tea plants have SI and long-term cross-pollination,which limits the progress of genetic research and variety improvement.However,the mechanism of SI in tea plants is still a mystery.Herein,microscopic observation showed that the pollen tube could pass through the base of style and enter the ovary cavity after 48 h of self-pollination at different flowering stages,and the SI intensity at bud stage and full bloom stage was lower than initial bloom stage.RNA-seq analysis showed that 1,463 and 1,409 differentially expressed genes(DEGs)were associated with low SI at bud stage and full bloom stage,respectively,and 507 DEGs were associated with SI at initial bloom stage.The results of qRT-PCR validation of 20 DEGs were consistent with the RNA-seq data.Furthermore,CsRNS,CsSRKL5 and CsSRKL8 specifically expressed in style,which may be related to the low SI at bud stage,and three CsACC genes may be related to the low SI at full bloom stage.The results provide useful information for understanding the mechanism of SI in tea plants.

Mycorrhiza improves plant growth and photosynthetic characteristics of tea plants in response to drought stress

Tea plants are sensitive to soil moisture deficit,with the level of soil water being a critical factor affecting their growth and quality.Arbuscular mycorrhizal fungi(AMF)can improve water and nutrient absorption,but it is not clear whether AMF can improve the photosynthetic characteristics of tea plants.A potted study was conducted to determine the effects of Claroideoglomus etunicatum on plant growth,leaf water status,pigment content,gas exchange,and chlorophyll fluorescence parameters in Camellia sinensis cv.Fuding Dabaicha under well-watered(WW)and drought stress(DS)conditions.Root mycorrhizal colonization and soil hyphal length were significantly reduced by the eightweek DS treatment.AMF inoculation displayed a significant increase in shoot and root biomass production.The relative water content,leaf water potential,nitrogen balance index,pigment content,maximum photometric effect(Fv/Fm,QY_max),and steady-state photometric effect Y(II)(QY_Lss)decreased dramatically,while the leaf water saturation deficit and steady-state non-photochemical fluorescence quenching(NPQ_Lss)generally increased under DS conditions.Mycorrhizal treatment induced significantly higher relative water content,leaf water potential,nitrogen balance index,pigment(chlorophyll,flavonoid,and anthocyanin)content,net photosynthesis rate,transpiration rate,stomatal conductance,intercellular CO_(2)concentration,QY_max,and QY_Lss;however,it resulted in a lower leaf water saturation deficit and NPQ_Lss under both WW and DS conditions,as compared with nonmycorrhizal plants.These results imply that AMF promoted tea plant growth and alleviated negative effects of DS by promoting gas exchange,regulating the water status of leaves,and regulating photosynthetic parameters.

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.