Study On The Interaction Mechanism Between Blumeria Graminis F.sp.tritici And Wheat Carrying Pm40

Blumeria graminis f.sp.tritici(Bgt)is an obligate biotrophic fungus that causes wheat powdery mildew,which is a devastating disease in wheat.Breeding resistant cultivars is an effective way to reduce the adverse impact of wheat powdery mildew.Pm40 offers a broad spectrum of resistance to Bgt,which suggests that it is likely to provide potentially durable resistance.However,little is known about the disease resistance mechanism of Pm40.In addition,the pathogenesis of this fungus and differences in the pathogenesis of the same pathogen at various resistance levels in hosts have not been determined as well.To have a better understanding of the interaction mechanism between wheat and Bgt,leaf tissues of both Pm40-expressing hexaploid wheat line L658 and its Pm40-deficient sister line L958were harvested at 0(without inoculation),6-,12-,24-,48-and 72-hours post-inoculation(hpi)with Bgt race 15 and then subjected to RNA sequencing(RNA-seq).To analyze the different gene expression patterns between compatible interaction and incompatible interaction,clean reads were mapped to the reference genome of Bgt isolate 96224 and wheat reference genome,respectively.In addition,we observed changes in fungal growth morphology at different time points as well as different resistance response between L658and L958 by staining.The differences in the physiological and biochemical levels between L658 and L958 were also analyzed,and the expression of pathogenic-related genes and disease-resistant genes was detected by real-time fluorescence quantitative PCR.The main results are as follows:1.The percentage of mapped reads of Bgt was very low in the two interactions at all time points,which is a common phenomenon in biotrophic fungi.However,there was a high correlation between percentage of reads mapped to the Bgt reference genome and biomass of the fungus within the leaf tissue during the growth process.Further functional annotations indicated that expression levels of genes encoding H~+-transporting ATPase,putative secreted effector proteins(PSEPs)and heat shock proteins(HSPs)were significantly up-regulated in compatible interactions compared with these levels in incompatible interactions,particularly at 72 hpi,which possibly played crucial roles in successfully establishing the pathogenesis of compatible interactions during late stages of inoculation.Moreover,KEGG pathway analysis suggested that genes involved in the endocytosis pathway were also important in compatible interactions2.H2O2 accumulation in L658 was significantly higher than that in L958 at 6 and 48hpi,and the enzymes activity and transcripts expression of peroxidase and catalase were suppressed in L658 compared with L958 as well.The downregulation of POD and CAT gene expression in L658 was likely related to the suppression of enzyme activity,which further led to the increase of H2O2 accumulation.Moreover,the first H2O2 accumulation in L658 during the stage from 6 to 12 hpi was possibly act as a second messenger to promote the second lasting and stronger H2O2 accumulation from 48 to 72 hpi,which further induced the HR reaction.3.The expression of genes involved in photosynthesis was globally inhibited in L658when compared with L958,which paralleled the decrease in photosynthesis parameters and chlorophyll fluorescence parameters in L658.The decrease in photosynthesis in L658 was mainly caused by non-stomatal limitation,and the downregulation of photosynthesis-related genes in L658 likely switched off photosynthesis activity to strengthen the defence reaction.However,only a small part of photosynthesis-related genes in L958 were downregulated,and the decrease of Pn in L958 was primally controlled by stomatal limitation rather than to regulate immune response.4.The expression of the salicylic acid-related genes non-expressor of pathogenesis related genes 1(NPR1),pathogenesis-related 1(PR1),and pathogenesis-related 5(PR5)was upregulated,while the expression of jasmonic acid-and ethylene-related genes was inhibited in L658 compared with in L958.The downregulated expression of JA/ET-related genes indicated that JA/ET levels were also decreased,which could be attributed to increased SA levels in L658.The increased SA and the upregulated expression of NPR1,PR1,and PR5 likely induced the HR in L658.However,the increase in JA/ET level and the high expression of PR10 and PR14 in L958 may act as negative regulators in the defence response to promote the establishment of susceptibility.