[Construction and sequence analysis of a drought-induced full-length cDNA library from Ammopiptanthus mongolicus]

Ammopiptanthus mongolicus shows very strong resistance to severe environments. To isolate drought-resistant genes and elucidate drought-resistant molecular mechanisms of the plant, we constructed a drought-induced full-length cDNA library using SMART (Switching mechanism at 5'-end of RNA transcript) technique. The phage titer of the unamplified library was 1.6 x 10(7) PFU/mL; the recombination percentage was 97.7%; and the sizes of most cloned cDNA fragments were around 1 kb. Three thousand positive clones were randomly selected and sequenced from their 5' ends, and a total of 1 450 Unigenes were identified. By Blast searches against the Nt, Nr and Swissprot databases, we found that 919 Unigenes (amount to 63.4%) showed significant similarity to the annotated genes, and the remaining 531 Unigenes (amount to 36.6%) represented novel genes without any annotation. Among the functional categories of the GO (Gene Ontology) classification, the terms related to physiological process, cellular process, binding, catalytic activity and cellular components were dominant. The next abundant terms were for organelle, protein complex, transporter activity and structural molecule activity. In addition, there were a significant proportion of the terms involved in stimulus response, gene expression regulation, regulation of physiological and biochemical processes and signal transduction. Many of the annotated Unigenes were found to be related to plant resistance to abiotic stresses, and expression analyses of 6 out of these genes by semi-quantitive RT-PCR confirmed their involvements in the response of A. mongolicus to drought stress. These results laid a foundation for the expression profile analysis and the cloning and characterization of drought-resistant genes from the plant in the future.