Plant genetic and molecular responses to water deficit

Plant productivity is severely affected by unfavourable environmental conditions (biotic and abiotic stresses). Among others, water deficit is the plant stress condition which mostly limits the quality and the quantity of plant products. Tolerance to water deficit is a polygenic trait strictly dependent on the coordinated expression of a large set of genes coding for proteins directly involved in stress-induced protection/repair mechanisms (dehydrins, chaperonins, enzymes for the synthesis of osmoprotectants and detoxifying compounds, and others) as well as genes involved in transducing the stress signal and regulating gene expression (transcription factors, kinases, phosphatases). Recently, research activities in the field evolved from the study of single genes directly involved in cellular stress tolerance (functional genes) to the identification and characterization of key regulatory genes involved in stress perception and transduction and able to rapidly and efficiently activate the complex gene network involved in the response to stress. The complexity of the events occurring in response to stress have been recently approached by genomics tools; in fact the analysis of transcriptome, proteome and metabolome of a plant tissue/cell in response to stress already allowed to have a global view of the cellular and molecular events occurring in response to water deficit, by the identification of genes activated and co-regulated by the stress conditions and the characterization of new signalling pathways. Moreover the recent application of forward and reverse genetic approaches, trough mutant collection development, screening and characterization, is giving a tremendous impulse to the identification of gene functions with key role in stress tolerance. The integration of data obtained by high-throughput genomic approaches, by means of powerful informatic tools, is allowing nowadays to rapidly identify of major genes/QTLs involved in stress tolerance, and to develop appropriate strategies to obtain, through genetic engineering or Marker Assisted Breeding (MAS) water stress tolerant plants. In the present review we reported the most recent results obtained, in both model and crop species, in the field of the plant genetics of water stress tolerance with special attention to new insights into the complex gene networks activated in response to water deficit (ABA-dependent and -indipendent pathways), the innovative genetic approaches to determine key gene functions (forward-reverse genetics), and the application of new genetic strategies to obtain tolerant genotypes (genetic engineering, QTL-based MAS).