| Powdery mildew caused by Erysiphe graminis DC is a severe wheat disease in China.To breed new varieties with efficient, broadspectrum, stable resistance to the disease, the understanding of resistance mechanism is of great importance. In our research, several techniques were used such as eDNA library construction of suppression subtractive hybridization (SSH), differential hybridization screening by high density dots membrane, EST (express sequence tags) and bioinformatics methods. The objective of the present research was to explore efficient methods to analyse high-thoughout gene expression, and to understand the resistance mechanism against powdery mildew at global transcriptional level. A primary gene expression profiling of the disease resistance in wheat would be obtained, with the matrial infected by E. graminis DC at early stage.The material used in the study was an BC5F4 line of æƒainong 3217 X Mardi er (powdery mildew resistant)?with Bainong 327 as the recurrent parent. The fungus E. gram mis race 15 epidemic in local regions of Beijing was used to inoculate the wheat material. Two kinds of cDNA libraries were constructed. One was a conventional cDNA library from wheat leaf challenged 72 hrs by E. graminis, and the other was a SSH eDNA library from wheat leaf challenged 24 hrs, 48 hrs and 72 hrs by the fungus. Totally 387 and 760 ESTs were acquired from the two libraries, respectively, and the ESTs similarity analysis using BLASTn and BLASTx software was implemented by comparing sequences in nr database of GenBank. By differential hybridization screening of the high-density dots membranes from the two libraries, 15 kinds of disease-resistance-related (DRR) genes were found in the conventional143library, and 65 kinds of DRR genes in SSH library. The primary gene expression profiling of powdery mildew resistance was revealed in wheat at the early stage of infection by E. gram mis.Through the analysis of acquired components in signal transduction, inositol- 1, 4,5-triphosphase signal pathway, salicylic acid pathway, MAP pathway were supposed to be involved in the reaction of powdery mildew resistance. Although the genes conditioning several key enzymes, such as ACC synthetase, ethylene-formingenzyme, I 2-oxophytodienoate reductase, were found in ethylene and jasmonic acid synthesis, to determine whether the two signal pathways take part in the disease resistance needs further study. Systemic acquired resistance (SAR) genes were rich not only in varieties but also in quantity. SAR genes that belong to five kinds of pathogenesisrelated proteins were observed in the present study. There were lots of evidence to support that PAL pathway takes a main part in phytoalexin synthesis in wheat against powdery mildew. There were also several kinds of enzyme genes involved in cell wall modification and suppressor genes related to pathogen growth that were identified in the ESTs obtained. In the study, cell survival system was also supposed to be activated when SAR system is induced to work. Genes for several proteinases mainly including cysteine-like proteinases were found, and these genes also appeared certain redundancy in the gene expression profiling, this phenomena might not be reported in disease resistance research before.In both conventional cDNA library and SSH eDNA library induced by Eryszphe graminis DC, some kinds of induced genes reported in other abiotic-stress selected eDNA libraries were acquired, such as heat shock protein, cold induced protein, aluminum induced4protein, salt stressed protein et al. After BLASTn and BLASTx analysis about ESTs of function unknown, many corresponding homolog were found from other stress selected cDNA libraries, these stresses include pathogen, salt, drought, cold, high temperature, culture144without light, ABA and so on. The result implies us that plant may have same mechanism to resist environmental stress in someway, and this result may also have a practical significance in breeding.The research is a...
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