Genome wide expression analysis of WRKY genes in tomato (Solanum lycopersicum) under drought stress

Regulatory genes play vital roles in survival of plants during environmental stress. WRKY transcription factors are major contributors among them. In tomato, WRKY transcription factor family contains 83 members. We have classified all tomato WRKY genes following well established classification of WRKY transcription factors in plant kingdom. Phylogenetic analysis of all these WRKY genes showed perfect correlation with this classification where proteins of each group formed a single clade. qPCR expression analysis of selected 62 WRKY genes was carried out under drought stress. The expression profiles revealed significant up-regulation of nine major WRKY genes in tomato. These nine genes were further investigated for the presence of specific cis-acting elements at the promoter region. Besides W-box and defense related elements, their promoter region was flanked frequently by abiotic stress responsive elements like ABRE, HSE and MBS. 5′UTR Py-rich stretch, known to promote high transcription levels, was also spotted at the promoter region of these genes. Drastic up-regulation was detected in SlWRKY58 (125 folds) and SlWRKY72 (36 folds) which portrays them as ideal targets for genetic manipulation to enhance drought tolerance.