Systems responses to progressive water stress in durum wheat

Durum wheat is susceptible to terminal drought which can greatly decrease grain yield. Breeding to improve crop yield is hampered by inadequate knowledge of how the physiological and metabolic changes caused by drought are related to gene expression. To gain better insight into mechanisms defining resistance to water stress we studied the physiological and transcriptome responses of three durum breeding lines varying for yield stability under drought. Parents of a mapping population (Lahn x Cham1) and a recombinant inbred line (RIL2219) showed lowered flag leaf relative water content, water potential and photosynthesis when subjected to controlled water stress time transient experiments over a six-day period. RIL2219 lost less water and showed constitutively higher stomatal conductance, photosynthesis, transpiration, abscisic acid content and enhanced osmotic adjustment at equivalent leaf water compared to parents, thus defining a physiological strategy for high yield stability under water stress. Parallel analysis of the flag leaf transcriptome under stress uncovered global trends of early changes in regulatory pathways, reconfiguration of primary and secondary metabolism and lowered expression of transcripts in photosynthesis in all three lines. Differences in the number of genes, magnitude and profile of their expression response were also established amongst the lines with a high number belonging to regulatory pathways. In addition, we documented a large number of genes showing constitutive differences in leaf transcript expression between the genotypes at control non-stress conditions. Principal Coordinates Analysis uncovered a high level of structure in the transcriptome response to water stress in each wheat line suggesting genome-wide co-ordination of transcription. Utilising a systems-based approach of analysing the integrated wheat's response to water stress, in terms of biological robustness theory, the findings suggest that each durum line transcriptome responded to water stress in a genome-specific manner which contributes to an overall different strategy of resistance to water stress

Proteome changes in wild and modern wheat leaves upon drought stress by two-dimensional electrophoresis and nanoLC-ESI-MS/MS

To elucidate differentially expressed proteins and to further understand post-translational modifications of transcripts, full leaf proteome profiles of two wild emmer (Triticum turgidum ssp. dicoccoides TR39477 and TTD22) and one modern durum wheat (Triticum turgidum ssp. durum cv. KA +/- zA +/- ltan) genotypes were compared upon 9-day drought stress using two-dimensional gel electrophoresis and nano-scale liquid chromatographic electrospray ionization tandem mass spectrometry methods. The three genotypes compared exhibit distinctive physiological responses to drought as previously shown by our group. Results demonstrated that many of the proteins were common in both wild emmer and modern wheat proteomes; of which, 75 were detected as differentially expressed proteins. Several proteins identified in all proteomes exhibited drought regulated patterns of expression. A number of proteins were observed with higher expression levels in response to drought in wild genotypes compared to their modern relative. Eleven protein spots with low peptide matches were identified as candidate unique drought responsive proteins. Of the differentially expressed proteins, four were selected and further analyzed by quantitative real-time PCR at the transcriptome level to compare with the proteomic data. The present study provides protein level differences in response to drought in modern and wild genotypes of wheat that may account for the differences of the overall responses of these genotypes to drought. Such comparative proteomics analyses may aid in the better understanding of complex drought response and may suggest candidate genes for molecular breeding studies to improve tolerance against drought stress and, thus, to enhance yields