Abstract:

We constructed a cDNA library from the leaf of cucumber (Cucumis sativus L.) line JIN5-508 with high powdery mildew resistance based on the SMART technology，and checked the quality of this library. The recombinant rate of present library was 95.3%，the titer was 1.02 × 106 pfu · mL-1，and the average size of inserted cDNA fragments were about 0.5 kb. It indicated that one high quality cDNA library of cucumber was successfully constructed. Subsequently，8 352 clones were chosen randomly from this library，and 8 035 valid expressed sequence tags were generated from the 5′ end sequencing. The average length of ESTs were 838 bp. Bioinformatics analysis of EST data indicated the low redundancy of this library with a score of 56.9%，in which 3 467 unigenes including 953 contigs and 2 514 singletons were assembled. Genes that expressed with low abundance occupied 72.5% of total unigenes，indicating the good complexity of gene expression in this library. One thousand nine hundred and ninty-one unigenes could be assigned functional description. Among the unigenes with molecular function classification，bindingactivity and catalytic acitivity related proteins took up to 41.34% and 38.72%，respectively. Three unigenes with high homology to Arabidopsis thaliana powdery mildew resistance locus were also identified，which suggested this library could be useful for further identification and expression analysis of powdery mildew resistance genes in cucumber.

Key words: cucumber, powdery mildew, cDNA library, EST