Proteomic responses of tomato plants under drought and salinity stress

Understanding the ways that plants can tolerate drought and salinity is necessary to develop plants that can grow on potential agricultural lands that are otherwise non-productive. The expression of a broad spectrum of genes is thought to be regulated by exposure to environmental salinity and water-deficit stress, the major stresses of plants in arid regions. Plant responses to salt and to drought stress have much in common. Both of these stresses reduce the ability of the plants to take up water and this quickly causes reduction in plant growth rate. The overall goal of this project was to identify proteins involved in response to drought and salinity stress in tomato. Combined proteomic approaches, two dimensional gel electrophoresis (2 DE) and liquid chromatography mass spectrometry (LC-MS/MS), revealed the plasticity of gene expression by protein analysis during environmental stress. Tomato plants were exposed to various concentrations of salt (sodium chloride) and polyethylene glycol induced drought stress. Roots and mature leaves were collected at various time points post-treatments, and these tissues were subjected to two-dimensional gel electrophoresis. A computer image analysis software program, PDQuest (Bio-Rad) was applied to the 2 DE gels for detection of stained proteins, background subtraction and signal matching between treated and control samples. Following completion of the PDQuest analysis, specifically repressed and induced proteins were identified from control and treated tissues using tandem mass spectrometry. The systematic proteomic approaches led to the identification of 150 proteins (induced and repressed) from drought and salt stressed tomato plants. Of the 150 proteins identified, 35 spots/proteins were common to salt and drought stress. These 150 proteins fall into several functional categories that include transcription factors, protein kinases involved in signal transduction, enzymes involved in solute accumulation and water homeostasis, and stress tolerance proteins. Moreover, the induction of several similar proteins during salt and drought stress could indicate some degree of overlap or cross-talk between various signaling pathways during drought and salinity. Identification of a "tomato stress proteome" could lead to enhancement of drought/salinity stress tolerance in tomatoes through genetic manipulation.