| Taramix hispida, a halophyte with high capacity of salt tolerance, is an excellent model plantin plant salt tolerance research. Three cDNA libraries were constructed from the root tissues of T.hispida of well-watered and exposed to NaC1 (0.4 M NaCl)for 24 and 48 h, respectively (named ascontrol, 24 and 48 h library, respectively). Average primary titer of the three libraries was 1.0×10~6pfu, 1.4×10~6 pfu, 1.2×10~6 pfu, respectively, with a rate of recombination about 98.％. PCRdetection revealed that their average inserts size was respectively 0.8, 0.9, and 0.85 kb.A total of 7 726 expressed sequence tags(ESTs) were obtained through randomly selectedsequencing process, with the GenBank accession numbers of EG966290-EG974015. The total of 7726 ESTs represented 4 168 non-redundant unique transcripts including 1 142 contigs and 3 026singletons. Total of 4 508 ESTs showed there existed significant similarityto the sequences with thesequences in NCBI Nr database, which were further classfied into 11 functional categories based ontheir putative functions, i.e., protein synthesis (21.4％), Function unknown (15％), Transportfacilitation (12.2％), Metabolism (11.2％), Cell rescue, defense (7.3％), Energy (7.0％), Cellstructure (6.8％), Transcription (5.1％), Protein destination (4.8％), Signal transduction (4.1％) andCell growth, division (3.7％). It should be emphasized that a remarkable variability of number of cellstructure genes was found among the three libraries. The percent of the cell structure genes in 24 hlibrary was three times of the control and 48 h library.Nearly 860 ESTs involved in salt tolerance were found from the 3 cDNA librarilies. Amongthem, scavenging reactive oxygen species was the most aboundant one, accounting for 27％, stressrelated protein and protein synthesis accounted for 16％respectively. Protein synthesis and degrationwas 10％, followed by metabolism and energy, signal transduction and transport. The smallest weretranscription and osmolyte biosynthesis genes, accounting for 3％respectively.EST analysis showed that total 106 unique genes showed different expression patterns afterexposure to NaCl; among them, 34 genes were up-regulated, 27 genes were down-regulated and theother 45 genes were transiently down or up-regulated. Among these differentially regualted genes,H~+-ATPsynthase, ABA stress ripening protein, lipid transfer protein, metallothionein, germin-likeprotein, ERD15 and LEA5 were up-regulated; however, the frequency of ESTs of structural cell wallprotein, including proline-rich protein and xyloglucan endotransglucosylase/hydrolase protein etcwere down-regulated, and EF1αand eIF 5a were transiently down or up-regulated.To explore the differences expression mode between roots and leaves of T. hispida exposed toNaCl, eight unique transcripts of POD and seven unique transcripts of aquaporin were selected forexpression analysis using real-time reverse transcription-polymerase chain reaction (RT-PCR).Theresults showed that gene expression pattems of eight POD genes were similar with each other in roots and leaves of T. hispida after exposing to NaCl for 0, 24 and 48 h, with repressed at 24 h andrecovered at 48 h. The different time course expression patterns of aquapofin appeared between inroots and leaves of T. hispida, seven aquaporin transcripts were up-regulated under NaCl stress inroots, however, they were down-regulated in leaves.Totally, 25 full-length genes were cloned from T hispida. These genes involved in the celldefense, anti-disease, ion homeostasis and transport, water stress related protein, cell structure,protein synthase and degration, and signal transduction.Based on the above, it could be concluded that salt-tolerance mechanism of T. hispida is acomplex system, involving with the cooperation of many pathways, such as scavenging reactiveoxygen, cell wall component, signal tranduction and transcription regulating, transporting of waterand ions, protection of dehydration damage. The studies could be used as a foundation in thefuture comprehensive reseaches of the salt resistance molecular mechanism of T. hispida. Thecloning of stress-tolerance genes may offer some attractive candidate genes for genetic engineeringof trees.
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