Transcriptomic analysis reveals the gene regulatory networks involved in leaf and root response to osmotic stress in tomato

We performed a transcriptomic analysis on two tomato genotypes, M82 and Tondo, in response to a PEG-mediated osmotic treatment, mimicking water stress. The analysis was conducted separately on leaves and roots to characterize the specific response of these two organs. A total of 6,267 differentially expressed transcripts related to osmotic stress response was detected. The construction of gene co-expression networks defined the metabolic and signaling pathways of the common and specific responses of leaf and root. The common response was characterized by ABA-dependent and ABA-independent signaling pathways, and by the interconnection between ABA and JA signaling. The root specific response concerned genes involved in cell wall metabolism and remodeling, whereas the leaf specific response was principally related to leaf senescence and ethylene signaling. The transcription factors representing the hubs of these regulatory networks were identified. Some of them have not yet characterized and can represent novel candidates for tolerance. Finally, several genes showing a genotype-specific expression regulation in response to the treatment were detected. These genes may be involved in the different sensitivity to the osmotic treatment of the two tomato genotypes. In conclusion, this work shed new light on the regulatory networks occurring in tomato leaf and root under osmotic stress and set the base for an in-depth characterization of novel stress-related genes, that may represent potential candidates for improving tolerance to water stress in tomato.