Identification of salt-induced genes from Salicornia brachiata, an extreme halophyte through expressed sequence tags analysis

Salinity severely affects plant growth and development causing crop loss worldwide. We have isolated a large number of salt-induced genes as well as unknown and hypothetical genes from Salicornia brachiata Roxb. (Amaranthaceae). This is the first description of identification of genes in response to salinity stress in this extreme halophyte plant. Salicornia accumulates salt in its pith and survives even at 2 M NaCl under field conditions. For isolating salt responsive genes, cDNA subtractive hybridization was performed between control and 500 mM NaCl treated plants. Out of the 1200 recombinant clones, 930 sequences were submitted to the NCBI database (GenBank accession: EB484528 to EB485289 and EC906125 to EC906292). 789 ESTs showed matching with different genes in NCBI database. 4.8% ESTs belonged to stress-tolerant gene category and approximately 29% ESTs showed no homology with known functional gene sequences, thus classified as unknown or hypothetical. The detection of a large number of ESTs with unknown putative function in this species makes it an interesting contribution. The 90 unknown and hypothetical genes were selected to study their differential regulation by reverse Northern analysis for identifying their role in salinity tolerance. Interestingly, both up and down regulation at 500 mM NaCl were observed (21 and 10 genes, respectively). Northern analysis of two important salt tolerant genes, ASR1 (Abscisic acid stress ripening gene) and plasma membrane H(+)ATPase, showed the basal level of transcripts in control condition and an increase with NaCl treatment. ASR1 gene is made full length using 5' RACE and its potential role in imparting salt tolerance is being studied.