Identification and characterization of differentially expressed genes during incompatible interaction between the foliar rust Melampsora larici-populina and poplar.

Poplars are extensively cultivated worldwide, and their susceptibility to the foliar rust fungus leads to considerable damages in plantations. To better understand the molecular basis of poplar responses to the foliar rust, suppression subtractive hybridization was used to identify the potential important or novel genes involved in the Populus szechuanica infection by Melampsora larici-populina. A total of 515 expressed sequence tags (ESTs) with high quality were obtained and clustered into 66 contigs and 75 singletons to give a set of 141 uniESTs. The nucleotide Basic Local Alignment Search Tool (BLASTn) program was used to search for homologous sequences of the uniESTs in the GenBank database. Among them, 92.9% showed homology to the poplar genome, and 2% showed similarity to the rust fungus genome. In addition, homology to known genes was analyzed by the BLASTx algorithm, and approximately 50% of the uniESTs were significantly homologous to genes encoding proteins with known functions. Based on a reverse transcription-polymerase chain reaction (PCR) and quantitative PCR approach, five uniESTs were analyzed, and the results showed that the expression level of the thaumatin-like gene was highest at 72 h post-inoculation, and the pathogenesis-related protein 1 gene was highest at 48 h post-inoculation. The information generated in this study provides new clues to aid in the understanding of incompatibility between poplar and the foliar rust.