Identification and sequencing of ESTs from the halophyte grass Aeluropus littoralis

Aeluropus littoralis (Gouan) Parl. is a C4 perennial halophyte monocotyledonous plant belonging to the same family as wheat. Growing as weed in dry salty areas or marshes, it is salt-secreting, rhizomatous and is used as forage. It is diploid (2n=2X=14) and has a relative small genome of around 342 Mb. A. littoralis is highly salt-tolerant since this plant has the ability to secrete salt. Thus, A. littoralis has the potential to become an important genetic resource for biotechnological strategies to improve salt and drought tolerance in economically important crops such as wheat. We have constructed SSH (Suppression Subtractive Hybridization) cDNA libraries from root (RSD45) and leaf (LSD45) tissues of 45 days old plants grown in the presence of 300 mM NaCl. We have also constructed full-length cDNA library from 15 days old salt stressed (300 mM NaCl) roots (RSTL15). Sequencing revealed 25 and 42 independent transcripts from the RSD45 and LSD45 cDNA libraries respectively, in both cases this was less than 25% of the clones sequenced. In contrast, 425 (60%) of the clones from the RSTL15 library revealed independent transcripts. After comparison with protein databases using BlastX, 335 (68%) ESTs (Expressed Sequence Tag) were classified into putative known functions and unclassified proteins, 59 (12%) have homology only to unidentified homologous sequences. A total of 98 (20%) of the ESTs have no homologies to known sequences in the protein databases which can be considered as novel.