Vertical Comparison of Stress-Related Transcription Factors in the Genus Oryza

The genus Oryza, which includes the Asian (O. sativa) and African (O. glaberrima) cultivated rices and all of their 21 wild relatives, represents 15 million years of evolution. We compared the regulation of putative orthologous groups of stress related transcription factors (TFs) as an initial effort to address the question of functional conservation, and to dissect a continuum of stress response genetic network complexities that might have emerged during the closely spaced Oryza speciation and domestication events. Eight groups of putative orthologous TFs, including six DREB/CBF, one Myb4, and one bZIP-TGA10 were compared among cultivated and wild species representing most of the known diploid genomes (AA, BB, CC, EE, FF), in terms of expression patterns across a battery of stress regimes (cold, heat, salinity, rapid dehydration) and regulatory information content of upstream regions of each gene. Two important trends had emerged from these studies. First, for most of the genes, extensive differences in expression pattern and regulatory information content were evident even among the orthologs of species (cultivated or wild) within the AA genome-group. Second, for few of the genes, patterns of regulatory conservation are evident even between species that belong to distantly related genomes. These trends suggest both functional conservation and specialization of orthologous stress-related TFs, perhaps indicative of the regulatory changes required for the specific ecological niches of each species. The potential implications of these patterns to stress adaptation capacity will be discussed within the context of the available physiological data.