Drought is an important environmental factor limiting the productivity of various crops worldwide. The development of crop cultivars with improved adaptation to drought is a major goal in many crop breeding programs. In addition to classical breeding approaches, genetic transformation to introduce candidate genes into plants for better tolerance to water deficit has been successfully developed. Pathogenesis-related proteins (PR proteins) are defined as plant proteins induced in response to pathogen attack. However, it is known that these proteins may also be involved in response to abiotic stresses. The objective of this study was to transform tobacco plants (as plant model for subsequent analysis of cultivated plant such as citrus) with a PR-4b protein from Theobroma cacao (TcPR-4b) and to select and test the tolerance of such transformed plants to water/osmotic stress. First, an in silico analysis of the TcPR-4b using the BLAST, Pfam,InterProScan, ORF-Finder programs, as well as a search on Cocoa GenDB databank were performed. The TcPR-4b belongs to a small family of PR-4 proteins whose members were mainly located on the chromosomes 5 (five genes) and 10 (one gene). The complete TcPR-4b sequence is 802 bp in length and contains two exons (171 and 258 bp), and one intron (82 bp); the corresponding protein is 142 amino acids in length. For plant transformation experiment, the TcPR-4b cDNA (from cacao-M. perniciosa interaction library) was cloned into the pGem- T Easy vector then subcloned on the pCambia binary vector 1390. Then, Agrobacterium tumefaciens strain EHA 105 was transformed with the35S::TcPR-4b::pCambia construction, and the transformed A. tumefaciens used for Nicotiana tabacum cv.Havana transformation by co-cultivation of leaf segments in selection medium. Transformed shoots from three transformation events are under selection for subsequent in vitro water/osmotic stress, using, among others, mannitol and NaCl. Funding Agency: FAPESB, CNPq, CAPES, EMBRAP