Abiotic stresses such as cold, salinity, drought, wounding, and heavy metal contamination adversely affect crop productivity throughout the world. Prosopis juliflora is a phreatophyte that can tolerate severe adverse environmental conditions such as drought, salinity, and heavy metal contamination. As a first step towards the characterization of genes that contribute to combating abiotic stress, construction and analysis of a cDNA library of P. juliflora genes is reported here. Random expressed sequence tag (EST) sequencing of 1750 clones produced 1467 high-quality reads. These clones were classified into functional categories, and BLAST comparisons revealed that 114 clones were homologous to genes implicated in stress response(s) and included heat shock proteins, metallothioneins, lipid transfer proteins, and late embryogenesis abundant proteins. Of the ESTs analyzed, 26% showed homology to previously uncharacterized genes in the databases. Fifty-two clones from this category were selected for reverse Northern analysis: 21 were shown to be upregulated and 16 downregulated. The results obtained by reverse Northern analysis were confirmed by Northern analysis. Clustering of the 1467 ESTs produced a total of 295 contigs encompassing 790 ESTs, resulting in a 54.2% redundancy. Two of the abundant genes coding for a nonspecific lipid transfer protein and late embryogenesis abundant protein were sequenced completely. Northern analysis (after polyethylene glycol stress) of the 2 genes was carried out. The implications of the analyzed genes in abiotic stress tolerance are also discussed.

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Abiotic stress is the principal cause of crop failure worldwide. Prosopis juliflora is a hardy plant reported to be tolerant to drought, salinity, extremes of soil pH, and heavy metal stress. Here, we report the characterization of a cDNA clone for a putative nonspecific lipid transfer protein (Pj LTP1) found abundantly in a drought stressed leaf cDNA library of P. juliflora and its promoter. A multiple sequence analysis of Pj LTP1 with wellestablished and officially designated nonspecific lipid transfer proteins allergens revealed high similarity at the amino acid level. Northern analysis of Pj LTP1 in P. juliflora leaves under oxidative stress revealed steady upregulation at the time points analyzed. A 929-bp fragment was isolated from the 5′ end of Pj LTP1, and transient reporter gene expression studies revealed it to be a functional promoter. Several cis-acting elements previously reported to function in stress response were found in this promoter. The possible reasons for changes in gene expression during stress in relation to the host plant's stress tolerance mechanisms are discussed.

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