Construction of a full-length cDNA library of Shatangju and cloning of pathogenesis-related protein gene

To better understand the molecular mechanisms underlying metabolism，development，disease resistance and quality of citrus，we constructed a full-length cDNA library from Citrus Shatangju（seedless）by using SMART™ technology. This high quality cDNA library featured as a storage capacity of 1.36 × 106 with more than 95% recombinant，containing a wide range of insert size from 0.6-2 kb. 224 clones were randomly picked up from the library and sequenced，36% of the clones were full length cDNAs. One of them，pathogenesis-related protein gene was submitted to GenBank with accesses number KJ000019. Bioinformatics analysis found that the full-length of pathogenesis-related protein cDNA was 707 bp，with a CDS of 459 bp，a 43 bp 5′UTR and a 235 bp 3′UTR，encoding a protein with 143 amino acid residues，the corresponding genomic sequence contained one intron with 193 bp. The molecular weight of the protein was 15.4 ku，with isoelectric point（pI）value of 6.96. The pathogenesis-related protein was predicted to have a signal peptide with 22 amino acid residences，which guided the protein to secreted to the outside of cell，and a Barwin domain，which responsed to fungi and bacteria with chitinase activity. The results indicated that， construction of this high quality cDNA library would be valuable to clone candidate genes，enhancing our understanding to the physiological metabolic processes of citrus，the obtained pathogenesis-related protein was valuable to diseaseresistant engineering.