Construction Of Suppression Subtractive Hybridization Libraries Of Tamarix.Spp. Under Drought Stress And Analysis Of Est

To investigate gene expression of Tamarix sp. under drought stress, cDNA from Tamarix species treated with drought stress as tester and cDNA in normal growth condition as driver, suppression subtractive hybridization (SSH) was employed to construct subtracted cDNA libraries of Tamarix hispida Willd and Tamarix ramosissima Ledeb.The Tamarix hispida Willd root SSH library was analyzed. DNA sequencing was conducted on 192 white clones, and 125 high quality sequences were generated under the accession numbers of CN121095-CN121219 in GenBank. Results of BLASTX search showed that a total of 17 sequences were homologous to known drought resistance genes, which encoded Mn-SOD, myb related protein, zinc finger protein etc.The Tamarix ramosissima Ledeb leaf SSH library was also analyzed. A total of 384 positive clones were sequenced, and 347 high quality sequences were obtained and registered in GenBank (CV794679-CV795025).BLASTX analysis of the EST collection generated from T. ramosissima library indicated that 144 ESTs were homologous to known functions genes, and 24 ESTs were homologous to genes with unknown or hypothetical functions. The rest 179 ESTs matched no sequences in publish database and may represented novel sequences. The 168 sequences matched to known proteins were further grouped into 13 categories based on their annotated functions. Among them, expressed abundant genes mainly fell into the categories of Metabolism and Photosynthesis, responding to 16.7% and 14.9% of all ESTs respectively. A total of 88 ESTs related to drought resistance were obtained which represented 67 unigenes, these ESTs were further classified into 11 categories according to the roles of their encoding proteins in drought tolerance These categories were: photosynthesis, signaling, stress/defense proteins, metabolism, detoxification enzyme, protein degradation, membrance fluidity, protein synthesis, osmoprotectan synthesis, transmembrane transport and transcriptional regulators. Most of these genes were associated with photosynthesis, signal, metabolism, stress protein and detoxification enzyme, representing 11.30%, 8.93%, 7.74%, 7.74% and 7.14% of identified genes respectively, which suggested they may play important roles during drought stress resistance in Tamarix species.Important drought resistance genes we obtained in T.ramosissima include calcium-dependent protein kinase 3, calmodulin, manganese superoxide dismutase, glutathione reductase, dehydration-responsive protein RD22, drought-induced proteinl, eukaryotic translation initiation factor 5A-2, ubiquitin-conjugating protein, malate dehydrogenase and S-adenosylmethionine synthetase, ect.