No Time to Waste: Transcriptome Study Reveals that Drought Tolerance in Barley May Be Attributed to Stressed-Like Expression Patterns that Exist before the Occurrence of Stress

Abstract

Plant survival in adverse environmental conditions requires a substantial change in the metabolism, which is reflected by the extensive transcriptome rebuilding upon the occurrence of the stress. Therefore, transcriptomic studies offer an insight into the mechanisms of plant stress responses. Here, we present the results of global gene expression profiling of roots and leaves of two barley genotypes with contrasting ability to cope with drought stress. Our analysis suggests that drought tolerance results from a certain level of transcription of stress-influenced genes that is present even before the onset of drought. Genes that predispose the plant to better drought survival play a role in the regulatory network of gene expression, including several transcription factors, translation regulators and structural components of ribosomes. An important group of genes is involved in signaling mechanisms, with significant contribution of hormone signaling pathways and an interplay between ABA, auxin, ethylene and brassinosteroid homeostasis. Signal transduction in a drought tolerant genotype may be more efficient through the expression of genes required for environmental sensing that are active already during normal water availability and are related to actin filaments and LIM domain proteins, which may function as osmotic biosensors. Better survival of drought may also be attributed to more effective processes of energy generation and more efficient chloroplasts biogenesis. Interestingly, our data suggest that several genes involved in a photosynthesis process are required for the establishment of effective drought response not only in leaves, but also in roots of barley. Thus, we propose a hypothesis that root plastids may turn into the anti-oxidative centers protecting root macromolecules from oxidative damage during drought stress. Specific genes and their potential role in building up a drought-tolerant barley phenotype is extensively discussed with special emphasis on processes that take place in barley roots. When possible, the interconnections between particular factors are emphasized to draw a broader picture of the molecular mechanisms of drought tolerance in barley.

Keywords: barley; drought tolerance; root system; stress; transcriptomics.

Figure 1

Hierarchical clustering of microarray data. Cam, CamB genotype; Mar, Maresi genotype; L, leaves; R, roots; c, control conditions; d, drought stress.

Figure 2

Spearman's rank correlation coefficient analysis comparing microarray and qPCR fold change data for selected DEGs. (A) comparison of microarray and qPCR data for genes differentially expressed in roots, (B) comparison of microarray and qPCR data for genes differentially expressed in leaves.

Figure 3

The comparison of a number of differentially expressed genes after drought treatment in CamB and Maresi leaves and roots.

Figure 4

Biological processes significantly enriched after GO analysis of 170 genes differentially expressed exclusively in CamB roots.

Figure 5

Selected genes putatively involved in drought tolerance in barley, that play a role in gene expression regulation processes. H–genes with higher expression in CamB than in Maresi in control conditions, L–genes with lower expression in CamB than in Maresi in control conditions, up–up-regulation of a gene in Maresi after drought treatment, down–down-regulation of a gene in Maresi after drought treatment. Gene description was based on the annotations available in Plaza Monocots database.

Figure 6

Selected genes putatively involved in drought tolerance in barley, that play a role in photosynthesis and energy regulation processes. H–genes with higher expression in CamB than in Maresi in control conditions, L–genes with lower expression in CamB than in Maresi in control conditions, up–up-regulation of a gene in Maresi after drought treatment, down–down-regulation of a gene in Maresi after drought treatment. Gene description was based on the annotations available in Plaza Monocots database.

Figure 7

Selected genes putatively involved in drought tolerance in barley, that play a role in signal transduction, cytoskeleton formation, vesicle transport and drought escape processes. H–genes with higher expression in CamB than in Maresi in control conditions, L–genes with lower expression in CamB than in Maresi in control conditions, up–up-regulation of a gene in Maresi after drought treatment, down–down-regulation of a gene in Maresi after drought treatment. Gene description was based on the annotations available in Plaza Monocots database.