| Bacterial fruit blotch(BFB)caused by the Gram-negative bacterium Acidovoraxcitrulli is considered as one of the most severeseed-borne devastating and quarantine disease worldwide,severely a ects the marketability of cucurbits includingboth watermelon and melon.Since the first report in 1998,it has been spread fast in China and the incidence is rising across the country in recent years.BFB has caused millions of dollars in losses inmany watermelon/melon-producing and regions of China.A.citrulli strains have been divided into two distinct groups based ongreat genetic diversity: group I(pslb65)strainshave been mainly isolated from melon hosts and the virulent on melon and watermelon are similar,while group II(AAC00-1)have been generally isolated from and are highly virulenton watermelon and the mean BFB severity forgroup II strains(AAC00-1)on watermelon wassignificantlygreater than group I.In contrast,The mean BFB severity forgroup II strains(AAC00-1)on melon was not significantly greater than group I.In this study,the transcriptional profiles of melon and watermelon seedlings infected with different strains were analysed at three different time points using RNA-squencing(RNA-Seq)technique.The metabolic pathways related to disease resistance including plant-pathogen interaction,phenylpropanoid biosynthesis and photosynthesis antenna proteins were identified,as well as the defense-related genes in these pathways were excavated,which reveal different pathogenicity of two different subgroup strains,the results will contribute to the data support for the mechanism of the host response to two different subgroup strains.The preliminary results are summarized as follows:1.The susceptible melon “IVF667” and watermelon “Hua xin 182” were used to analyze the gene expression profiling of plant at 6 h,12 h and 72 h post inoculationfortranscriptomic analysis.Melon and watermelon samples infected with pslb65 were obtained 670,727,398 clean reads and samples infected with AAC00-1 were obtained 695,501,790 clean reads.About 90% total mapped reads were matched to Cucumis melo and Citrullus lanatusreference genome.2.The expression genes of the interaction between pslb65/AAC00-1 and watermelon/melon were significantly different,and significantly down-regulated genes were more than up-regulated genes after the infection with A.citrulli.The analysis of differentially expressed genes(DEGs)showed thatsignificantly down-regulated genes accounted for 65.50%,62.30% and 68.33%in melon seedlingsafter infected with pslb65 at 6 h(MP6),12 h(MP12)and 72 h(MP72)post inoculation.While 49.74%,68.57% and 65.47%genes were significantly down-regulated in watermelon seedlingsafter infected with pslb65 at 6 h(WP6),12 h(WP12)and 72 h(WP72)post inoculation.The percentage of significantly down-regulatedgenes were 54.47%,52.10% and 62.77%in melon seedlings with the infection of AAC00-1at 6 h(MA6),12 h(MA12)and 72 h(MA72)post inoculation.While 53.42%,53.75%and 48.93%significantly down-regulatedgenes were identified in watermelon seedlings with the infection of AAC00-1at 6 h(WA6),12 h(WA12)and 72 h(WA72)post inoculation.The significant difference between the number of DEGs and the proportion of down regulated genes in watermelon/melon in response to different strains reflected the difference of pathogenicitycaused by corresponding pathogens.3.GO functional enrichment analysis was used to understand the specific biological functions of DEGs after the infection with pslb65/AAC00-1 inwatermelon/melon.Unigenes in Gene Ontology(GO)function showed that the significantly enrichedfunction is cellular metabolic process,localization,transport and the thylakoid and photosynthetic membrane in Cellular Component and the transcription factor activity,oxidoreductase activity,coenzyme binding,catalytic activity in molecular function.KEGG pathway analysis showed that thedifferential expressed genes were involved in resistance related metabolic pathways of plant-pathogen interaction,phenylpropanoid biosynthesis and photosynthesis antenna proteins.Genes related to three pathways were up-regulated or down regulated in order to response two strains after inoculated with A.citrulli pslb65 and AAC00-1.While genes related to three pathways in melon seedlings were almost down-regulated along with enhanced stresses caused by pslb65 infection,indicating that three pathways were suppressed.While genes involved in three pathways were up-regulated to enhance the defense of watermelon to pslb65.The suppressed effects of genes involved in three pathways in the AAC00-1 infection of melon were lower than the pslb65 infection.These genes were almost up-regulated after the AAC00-1 infection of watermelon seedlings,suggesting that these up-regulated genes may play an important role in the resistance to AAC00-1 in watermelon plant.Through the above analysis,some genes related with plant-pathogen,phenylpropanoid biosynthesisand photosynthesis antenna proteins pathway were identified and the pathogenicity difference ofcaused by pslb65/AAC00-1according tothe expression patterns of DEGsin melon or watermelon.4.Twelve geneswere subjected toqRT-PCR and the results validatedthe Illumina sequencingconclusions,indicatingthat thedatafrom RNA-Seqwas accurateandreliable. |
