Dehydration-responsive nuclear proteome of rice (Oryza sativa L.) illustrates protein network, novel regulators of cellular adaptation, and evolutionary perspective.

Water deficit or dehydration is the most crucial environmental constraint on plant growth and development and crop productivity. It has been postulated that plants respond and adapt to dehydration by altering their cellular metabolism and by activating various defense machineries. The nucleus, the regulatory hub of the eukaryotic cell, is a dynamic system and a repository of various macromolecules that serve as modulators of cell signaling dictating the cell fate decision. To better understand the molecular mechanisms of dehydration-responsive adaptation in plants, we developed a comprehensive nuclear proteome of rice. The proteome was determined using a sequential method of organellar enrichment followed by two-dimensional electrophoresis-based protein identification by LC-ESI-MS/MS. We initially screened several commercial rice varieties and parental lines and established their relative dehydration tolerance. The differential display of nuclear proteins in the tolerant variety under study revealed 150 spots that showed changes in their intensities by more than 2.5-fold. The proteomics analysis led to the identification of 109 differentially regulated proteins presumably involved in a variety of functions, including transcriptional regulation and chromatin remodeling, signaling and gene regulation, cell defense and rescue, and protein degradation. The dehydration-responsive nuclear proteome revealed a coordinated response involving both regulatory and functional proteins, impinging upon the molecular mechanism of dehydration adaptation. Furthermore a comparison between the dehydration-responsive nuclear proteome of rice and that of a legume, the chickpea, showed an evolutionary divergence in dehydration response comprising a few conserved proteins, whereas most of the proteins may be involved in crop-specific adaptation. These results might help in understanding the spectrum of nuclear proteins and the biological processes they control under dehydration as well as having implications for strategies to improve dehydration tolerance in plants.