Transcriptomic Profile Of Tobacco In Response To Alternaria Longipes And Alternaria Alternata Infections

Tobacco brown spot caused by Alternaria fungal species is one of the most damaging diseases,and results in significant yield losses.However,little is known about the systematic response of tobacco to this fungal infection,Therefore,it is undoubtedly that has a great significance to systematically study the changes of gene expression for tobacco undergoing brown spot.In this paper,tobacco cultivars V2(N.tabacum L.cv.V2)and NC89(N.tabacum L.cv.NC89)were examined after the inoculation of either Alternaria longipes(AL)or Alternaria alternata(AA).Though de novo assembling the tobacco leaf transcriptome,the difference of gene expression profile of tobacco were determined,which infected by different Alternaria species for different time points.First,the conidial suspensions of A.longipes and A.alternata were used to inoculate the leaf from the aseptic seedlings of V2 and NC89.Two cultivars and two Alternaria strains yield four cultivar-pathogen combinations:V2-AL,V2-AA,NC89-AL and NC89-AA.Every combination was harvested at three time points,that is,6,24,and 72 hours post inoculation,respectively.Leaf tissues from healthy aseptic tobacco seed-ling were the controls for the experiment.Total RNA was isolated from each sample and was sequencing after cDNA library preparation.The tobacco reference transcriptome was obtained after assembling the RNA-Seq data.We studied the gene expression profile of each cultivar-pathogen combination comparing with control,and identified a large number of differentially expressed genes,gene ontology enrichment analysis of the differentially expressed genes revealed key components during the fungal infection,which included regulation of gene expression(GO:0010468),regulation of RNA metabolic process(GO:0051252),tetrapyrrole binding(G0:0046906)and external encapsulating structure(G0:0030312).Meanwhile,eight differentially expressed genes shared among all combinations were identified,which may relate with basic defenses of tobacco.Further analyses of the continuously up-/down-regulated genes,the NBS resistance genes and WRKY transcript factor genes demonstrated that the gene expression profile upon fungal infection was contingent on the specific cultivar and pathogen.Most of genes related with plant-pathogen interaction pathway were up-regulated expressed in tobacco after inoculation with Alternaria fungi,but there were some differences for different cultivars-pathogen combinations.And two sets gene expression profile maybe related to different Alternaria species or different tobacco cultivars using weighted gene co-expression network analysis(WGCNA)analysis.This study systematically studied the gene expression profile of tobacco responsed to A.longipes and A.alternata infections,and the results preliminarily showed the interaction between Alternaria fungi and tobacco cultivars.In conclusion,this study provides a solid foundation for the investigation of plant-pathogen interaction.It will not only assist in the discovery and annotation of important genes in plant defense response,physiology and metabolism,but also is of great importance for disease prevention and molecular breeding.