| Wheat powdery mildew, caused by an obligate biotroph Blumeria graminis f. sp. tritici(Bgt), is one of the common pathogenic diseases of bread wheat worldwide and causing significant loss of yield. As concern, a certain number of pathogen-resistant genes have been transmitted to the susceptible common wheat from its wild relatives through traditional breeding and displayed varying degrees of resistance to different Pm types. Recently, there have been many genomic and transcriptomic studies for unravelling the molecular mechanisms underlying this host-pathogen interaction, but proteomic studies in this regard are almost negligible. Therefore, a proteomic study was conducted to explain the molecular mechanism underlying the powdery mildew resistance response in wheat.A powdery mildew resistance homozygous common wheat line N0308 harboring a resistance gene PmG25 from the cross between wild emmer wheat(T. dicoccoides) accession ‘G25’ and powdery mildew susceptible Chinese elite common wheat line Shaan 253, was used in the study. Following inoculation with Bgt isolate E09, a proteomic profile of wheat leaves was constructed by two-dimensional gel electrophoresis(2-DE) coupled with mass spectrometry analyses. A defensive network mediated by a race-specific resistance gene has been proposed. Proteomic expression of selected genes was validated at transcriptional level by real-time quantitative reverse transcription-polymerase chain reaction(qRT-PCR) analysis. The main findings of the study may be pointed out as follows:1. Using a cut-off of minimum 1.5-fold change and a p-value of < 0.05, eighty seven reproducible protein spots on the 2-DE gels showed significant changes in abundance at 24, 48, and 72 h after inoculation with Bgt, as compared to non-inoculated plants. Among them, 37 spots were decreased in abundance and the rest being increased or induced upon Bgt inoculation. Mass spectrometry analysis using the NCBInr database of Triticum aestivum(48 spots) and closely related species in the Triticum genus(31 spots) allowed the identification of 79 spots. Functional annotation of these proteins revealed that they were putatively involved diverse metabolic pathways including stress and disease resistance(20%), photosynthesis(14%), sugar metabolism(14%), translation and transcription(11%), energy regulation(6%), protein turnover(6%), secondary metabolism(9%), gene expression(4%), and cellular reorganization(3%).2. Up-accumulation of several disease resistance proteins were observed in Bgt-inoculated samples that belong to CC-NBS-LRR type resistant gene family. Importantly, three proteins showed sequence homology to powdery mildew resistance gene Pm3 b, and another was identified as Pm3b-like disease resistance protein 2Q4. The other proteins identified in this class were disease resistance protein CNL2, LRR14 and RPM1. Besides this, two molecular chaperons, two pathogenesis-related proteins and some other defense-related proteins that are well known for generating hypersensitive response and chemical defense against pathogen were also over-expressed.3. As a whole, the present proteomic dataset proposed the interplay of several complex metabolic pathways mediated by the resistance gene Pm3 b in triggering a race-specific resistance response of wheat to Bgt infection. Suppression of major photosynthetic proteins and enhancement of proteins related to sugar metabolism and energy pathways may indicate that elevated energy is required to activate defense responses and maintaining cellular homeostasis at various times during pathogen attack. Differential regulation of secondary metabolites, and transcription and translation regulators indicated their important role in the subsequent molecular events.4. The qRT-PCR data of 17 selected genes showed that the transcriptional expression of six genes were in consistent with the proteomic data. Opposite expression profile between protein and mRNA abundance was observed for one gene. The transcriptional regulation of rest genes was partially in agreement with the proteomic results. The post-transcriptional regulation of protein might be accounted for these discrepancies. This result provides us a vital clue that Bgt might perturb the protein concentration regardless of transcriptional process for certain genes in wheat plant. |
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