| Drought is one of the major environmental factors that affect the growth of plant and account for significant reduction in the yields of crops. An effective approach to solve this problem is to produce drought-tolerant crops. Therefore, comparative functional genomics studies are required to identify key genes responsible for dehydration and drought stress tolerance as well as candidate genes for genetic engineering of drought stress tolerance in crop plants. Grimmia pilifera, as a common drought tolerant moss, grows in habitats of rocky outcrops, having a high ability in resisting drought stress. Grimmia pilifera may serve as a rich genetic resource for the identification of novel genes associated with environmental stress and dehydration toleranceTo further understand the mechanisms of Grimmia pilifera responding to drought stress, we constructed a cDNA library from the gametophyte of Grimmia pilifera, and the titer of the library was 2.8×105 pfu/mL. PCR amplification revealed that the insert cDNA fragments ranged mostly from 500 to 2000bp, with an average length of 800 bp, and the percentage of recombinants was 91.7%. A total of 1045 clones were randomly picked and subjected to 5'end single-pass sequencing from the library. After trimming of vector/adaptor sequences and discarding of low quality or short clones,996 high-quality ESTs were generated with GenBank accession numbers from GR307103 to GR308098. The total 996 ESTs represented 875 non-redundant unique transcripts, including 62 contigs and 813 singletons. Among them,625 Unigenes showed similarities to gene sequences in the non-redundant (Nr) GenBank database, and the other 250 had no similarities. The database-matched Unigene were further grouped into 16 functions according to GO assignments, i.e, physiological process(21.17%), cellular process(14.60%), cell(13.63%), catalytic activity(13.14%), binding(10.71%), organelle(10.46%), protein complex(7.54%), structural molecule activity(3.41%), response to stimulus(1.95%), transporter activity(1.22%), antioxidant activity(0.97%), translation regulator activity(0.24%), enzyme regulator activity(0.24%), motor activity(0.24%), transcription regulator activity(0.24%), and regulation of biological process(0.24%).In total,68 Unigenes involved in signal transduction, reactive oxygen scavengers, protection and repair of photosynthesis system, protein synthesis and degradation, metabolism, materials transport and ionic equilibrium, cell wall and cell defense, and tress response were identified.Real-time quantitative PCR was used for identification of expression profiles of 9 drought stress induced genes from Grimmia pilifera. The results showed that the expressions of the 9 genes were all induced by dehydration or rehydration, and the expression patterns of those genes were different.Four genes including ascorbate peroxidase, copper/zinc-superoxide dismutase, glutathione S-transferase and cysperoxiredoxin were obtained, and named GpAPX,GpSOD,GpGST and GpCysPrx. They were submitted to the GenBank databases with accession numbers from GU989311 to GU989314. Protein analysis was performed using bioinformatics software, and QRT-PCR was used to study the expression profile during dehydration and rehydration.The identification of the drought-resistance genes provided genetic resources for plant breeding and genetic engineering of crop plants. This work represented an important step in understanding the molecular mechanism of drought tolerance in Grimmia pilifera.
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