Transcriptional Profiling Implicates Novel Interactions between Abiotic Stress and Hormonal Responses in Thellungiella, a Close Relative of Arabidopsis  

Abstract

Thellungiella, an Arabidopsis (Arabidopsis thaliana)-related halophyte, is an emerging model species for studies designed to elucidate molecular mechanisms of abiotic stress tolerance. Using a cDNA microarray containing 3,628 unique sequences derived from previously described libraries of stress-induced cDNAs of the Yukon ecotype of Thellungiella salsuginea, we obtained transcript profiles of its response to cold, salinity, simulated drought, and rewatering after simulated drought. A total of 154 transcripts were differentially regulated under the conditions studied. Only six of these genes responded to all three stresses of drought, cold, and salinity, indicating a divergence among the end responses triggered by each of these stresses. Unlike in Arabidopsis, there were relatively few transcript changes in response to high salinity in this halophyte. Furthermore, the gene products represented among drought-responsive transcripts in Thellungiella associate a down-regulation of defenserelated transcripts with exposure to water deficits. This antagonistic interaction between drought and biotic stress response may demonstrate Thellungiella's ability to respond precisely to environmental stresses, thereby conserving energy and resources and maximizing its survival potential. Intriguingly, changes of transcript abundance in response to cold implicate the involvement of jasmonic acid. While transcripts associated with photosynthetic processes were repressed by cold, physiological responses in plants developed at low temperature suggest a novel mechanism for photosynthetic acclimation. Taken together, our results provide useful starting points for more in-depth analyses of Thellungiella's extreme stress tolerance.

Linking the Salt Transcriptome with Physiological Responses of a Salt-Resistant Populus Species as a Strategy to Identify Genes Important for Stress Acclimation

“…However, not all of the eight Arabidopsis genes showed the same responses to salt, drought, or osmotic stress as poplar genes, pointing to differences in stress regulation. Comparative analysis of salt cress and Arabidopsis transcriptomes also supported the idea that the regulation of some key genes may be different in salt-tolerant and salt-sensitive species (Gong et al, 2005;Wong et al, 2006), and our study is strong experimental evidence for this suggestion.…”

“…This probably reflects an accommodation for decreases in assimilation. Notably, similar responses have also been found in salt cress in response to excess salinity (Wong et al, 2006). Comparisons of stress transcriptomes of Arabidopsis also support the notion that down-regulated clusters mainly contain genes for developmental processes and metabolic adjustment (Ma and Bohnert, 2007).…”

“…Upon sudden salt exposure, both species activated genes involved in ribosomal functions, photosynthesis, cell growth, osmolyte production, and transport activities (Gong et al, 2005), whereas in salt-acclimated T. halophila plants, only a few genes were differentially regulated (Wong et al, 2006).…”

The Association Among Gene Expression Responses to Nine Abiotic Stress Treatments in Arabidopsis thaliana

“…Two defense-related genes were exclusively downregulated among all nine abiotic stress treatments (At3g57260 and At2g43600). Such downregulation could arise from stress-induced elevations of ABA phytohormone, which has been found to promote the downregulation of defense-related genes (Anderson et al 2004) and may therefore account for downregulation of defense-related genes under abiotic stress treatments (e.g., see Wong et al 2006). Given that the stress-general genes highlighted above have been identified on the basis of microarray data alone, it should be emphasized that the present analysis represents only a first step toward confirming and understanding their role in stress regulatory pathways.…”

“…The second approach accounted for variability in duplicate gene expression measures and identified genes for which the effects of stress treatments were large relative to variability associated with duplicate expression measurements (differential expression analysis). These two approaches correspond to criteria that have been used in previous studies to identify genes exhibiting expression responses to multiple stress treatments (e.g., Seki et al 2001Seki et al , 2002Seki et al , 2004Kreps et al 2002;Hazen et al 2003;Rensink et al 2005;Wong et al 2006).…”