Identification And Expression Analysis Of Differently Expressed Genes In Brassica Rapa Response To Plasmodiophora Brassicae Woron Infection

Clubroot disease casued by Plasmodiophora brassicae Wor.is a woldwide disease,which is also one of the main diseases of Brassica rapa.Clubroot disease casued severe damage in crop yield.To date,Clubroot disease is found at 17 provinces,cities and autonomous regions through a nationwide survey.Thous it can be seen that clubroot disease seriously affected the sustainable development of Chinese cabbage.In this study,we analyzed the transcription information of CR BJN3-2 and BJN3-2 inoculated with P.bra.ssicae at four time points,which were 0 hours,12 hours 72 hours and 96 hours after inoculation,in order to realize the dynamic changes of gene transcription of B.rapa under the stress of P.brassicae.Based on the results,we analyzed the signal transduction pathways involved in the interaction between Chinese cabbage and P.brassicae.We also identified 33 chitinase genes and the structure,evolution and chromosome location were analyzed.The response of ehitinase family gene to P.brassicae infection as well as clubroot disease development in susceptible line after chitin oligosaccharides pretreatment were investigated.These studies laid the foundation for further study on the molecular mechanism of resistance to P.brassicae.Main results are as follows:1.Eight pools of mRNA samples,two B.rapa cultivars CR BJN3-2 and BJN3-2 at four time points inoculated with P.brassicae which were 0 hours,12 hours 72 hours and 96 hours after inoculation were used to build libraries for RNA-Seq.A total of 180,185,005 reads were generated by 100-bp paired end sequencing from the eight cDNA libraries,constituting 35.4Gb of cDNA sequence.2.A total of 3812 DEGs were identified between CR BJN3-2 and BJN3-2.DFGs at four time points were 2056,1597,1569 and 1452,respectively.While only 83 genes were up-regulated and 321 weredown-regulated at all four timepoints.Compared with BJN 3-2,987,587,670 and 574 DEGs were up-regulated at four timepoints.Following,P,brassicae inoculation,1069,1010,899 and 878 DEGs were down-regulated at t four timepoints.3355 DEGs were found to have significant in the GO,1034 in the COG,788 in the KEGG.3.The initial step in the defense response of plants to the presence of a pathogen is the conserved PAMPs detected by PRRs.Among the 23 differentially expressed PRRs,14 were induced in BJN3-2.and 9 were induced in CR BJN3-2.4.The NB-LRR containing R gene is a crucial component of ETI,as it detects and binds to pathogen effectors.In our study,of the 15 differentially expressed R proteins between the two NILs,only two genes encoding NBS-LRR proteins were down-regulated in CR BJN3-2 compared with BJN3-2.5.One of the features of the defense response of plants is the production of PR proteins that are induced specifically in pathological or related situations.After inoculation with P.brassicae,18 PR proteins(including 7 PR proteins,5 thaumatin family proteins.and 6 lipid transfer proleins)were differentially regulated between CRBJN3-2 and BJN3-2.All the 18 PR proteins were up-regulated in CR BJN3-2 following inoculation with P.brassicae.6.Plant hormone mediated the signal transduction response to the stress of P.brassicae.After inoculation with P.brassicae,our resluts showed an induced SA signal pathway and repressed JA/ET signal pathway in Resistant NIL.7.Of the 34 genes involved in cell division and expansion identified in the current study,only 11 genes were up-regulated in the clubroot-resistant NIL after inoculation,with the remaining 23 genes being down-regulated.8.In this study.we identified 33 chitinase genes and the structure.evolution and chromosome location were analyzed.Based on multiple sequence alignment and phylogenetic analysis,chitinase proteins cluster into five classes,and the distribution of the chitinase genes on each chromosome were uneven.All 33 chitinase genes contained 1-7 cis-elements related to stress or hormone response.Chitinase genes in the same class shared similar structure,conserved domains and motifs.9.In the present study,during P.brassicae infection(0-20dai),the expression of at least 14 B.rapa chitinases were induced,and all of them rapidly responded to P.brassicae inoculation at initial stage(0,5-ldai).However,they showed different expression patterns in the incompatible/compatible interactions.After chitin treatment,the expression level of selected chitinase genes were increased gradually during early time points(0.5-3dai)in both NILs,then declined to a lower level during the later treatment(3-20dai),still higher than the control sample.