Gene Expression Analysis In Early Stage Induced By Powdery Mildew In Wheat

Powdery mildew is a serious disease of wheat in China, which is caused by the fungus Erysiphe graminis DC. It can dramatically reduce crop yield and threaten our national food safty. So it is urgent to study the disease-resistant mechanism at the integral level and to improve disease resistance in wheat using the modern molecular biology.In this research, a cDNA library was constructed by suppression subtractive hybridization (SSH) based on the Mardler/Bainong3217 BC5F7 as a tester, one of near-isogenic lines (NILs) of wheat carrying a powdery mildew resistance gene Pm2 and its recurrent parent Bainong3217 as a driver. Our purpose is to identify early expressing genes induced by powdery mildew (Erysiphe graminis DC) in wheat and we hope to elucidate the possible resistant mechanism of wheat.The harvest time points include 0.5, 1, 3, 6, 12, 16, 20 hai (hours after inoculation), which are crucial time-points for the Pm2-mediated hypersensitive response, were determined according to Li et al. (Plant Pathology, 2005, In pressed). Four thousand two hundred twenty four clones were stored and plasmids DNAs were extracted from 864 clones. Six hundred sixty-seven good quality plasmids were subsequent to be sequenced. ESTs similarity analysis via BLASTx and BLASTn software appeared that 373 ESTs matched proteins or genes, including 74 unknown proteins. Moreover, 254 ESTs did not appear homology to sequences with known functions. After redundancy ESTs were removed, 207 uniESTs matching the genes and proteins that involved in pathogen response, energy metabolism, signal transduction, ect. were obtained. As a result, the gene expression profile before 24hai was constructed.Compared with the ESTs in the SSH library constructed with the same material but harvested at 24, 48, 72hai (Luo et al., 2002), more R genes (36.8% of total disease/defense genes) and more genes of the signal transduction pathways (12% of total expressed genes analyzed ) were found in our SSH library before 24 hai. In addition, genes linked to Ca2+ signal and ubiquitin degradation system were considerably caught. Extraordinarily, 26S proteasome and transcription-related genes were exclusively detected. In the SSH library after 24hai, however, only 2 types of R genes out of total disase/defence genes (0.06%) , 6% of signal genes out of total gene expression analyzed and much more SAR (systemic acquired resistance)-related genes and PR(pathogenesis-related protein) genes appeared.According to some published papers, a lot of genes classified into signal transduction, intracellular traffic, transcription and cell structure function in our SSH library were also involved in several kinds of stress responses, which appears to imply the analogous mechanism in the resistance process when plant faces all kinds of environmental stresses. Through the analysis on the gene expression at 0.5-20hai, the possible resistant mechanism of wheat powdery mildew was discussed.