Induced Expression Profiling Of Potato Genes Associated With Quantitative Resistance To Late Blight And Preliminary Exploring Of Quantitative Resistance Mechanism

On a global scale, potato (Solarium tuberosum L.) is the fourth largest crop species grown as a food source. However, late blight, caused by the oomycete pathogen Phytophthora infestans, is one of the world agriculture's most destructive plant diseases and has turned up throughout the world. Therefore, it is extensively concerned to prevent and cure this disease. Quantitative resistance is controlled by many interacting genes that can slow down the development of the pathogen at individual infection sites on the plant, and hence, lasts longer. Consequently, it has become an inevitable trend to improve the genetic resistance to P. infestans in breeding new quantitative cultivars of potato. Up to now, a number of quantitative trait loci (QTLs) for late blight have been mapped in many experimental populations of potato, and numerous differentially expressed genes associated with quantitative resistance have been identified. Nonetheless, very little is known about the dynamic expression patterns of these genes during P. infestans infection, the defense metabolism pathways and the signal transduction network associated with quantitative resistance to late blight. Therefore, based on 1009 differentially regulated expressed sequence tags (ESTs) associated with quantitative resistance to P. infestans, a comprehensive transcriptional analysis was performed under different treatments of P. infestans and abiotic factors with the cDNA microarray technology. In addition, the expression patterns of these ESTs in different potato cultivars (clone) were compared by microarray analysis. The purposes of this reseach are to elucidate the molecular basis of potato quantitative resistance, and provide a clue of valid application of this resistance and development of new strategy of controlling late blight. The main results are as follows:(1) The dynamic expression patterns of 1009 ESTs in the leaves of quantitative resistance potato clone (QR; CIP Code: 386209.10) were analyzed during P. infestans infection. Based on the criteria of a normalized expression ratio over 2.2-fold between the inoculated and control samples, a total of 669 significantly differentially expressed ESTs were identified. All the 669 ESTs were sequenced and used to search by BLASTn and BLASTx. After merging the repeated ones, 348 singleton ESTs were identified. Among these ESTs, 234 had significant matches with the functional genes or ESTs, whereas the rest (32.8%) were regarded as unknown-function genes because of their low sequence similarity. The ESTs with known function were classified into 13 categories, namely, cell defense, primary metabolism, secondary metabolism, energy metabolism, signal transduction, transcription, protein synthesis, protein fate, cellular transportation, cellular organization, protein with binding function, systemic response, and development. According to the expression paterns of identified potato genes, we discriminated distinct stages of potato defense against P. infestans, which not only unfolded the natural process of the pathogen infection but also revealed the timing of the events and the genes participating in each stage. Expression-profiling information would serve as a platform...