Root-transcriptome Responses to Water Deficit and Salt Stress During Early Barley Development

Global agricultural production suffers from yield losses due to extreme climate. Among these harsh conditions, water shortage and high soil salinity are the most prominent abiotic stress factors. To ensure survival, plants implement gene expression changes, which in turn lead to adaptive changes in physiological processes and pathways. The root system is the first plant organ that encounters such stresses. This study investigated changes in the transcriptome of seminal roots of barley seedlings exposed to abiotic drought and high salinity stress and a combination of both after six and 24 hours of treatment. Based on RNA-Seq analyses, differentially expressed genes (DEG) were identified and GO term analyses were performed. In total, more than 5,000 and 9,000 genes were declared as DEG after six and 24 hours, respectively. Comparison of these genes revealed, that more than 60% of the DEGs per treatment, that showed a response to long-term stress, were also responsive to short term stress. A combination of stresses resulted in the highest number of DEGs at both time points. Short-term combined stress resulted in over 3,000 DEGs that were unique for this treatment. Long-term stress response showed a substantial overlap with the drought and the combined treatment. In general, drought stress had a stronger impact on changes in gene expression than salt treatment. The direction of regulation depended on treatment-type and duration. A GO enrichment analysis identified 65 up-regulated and 123 down-regulated terms that were enriched in at least one treatment. Several up-regulated terms including ‘transcription factor activity’ and ‘regulation of metabolic processes’ were conserved among all treatments, indicating a general role in water deficit response. The term ‘catalytic activity’ was down regulated throughout all treatments. This study provides novel insights into stress-responsive genes in young barley roots and provides a resource for further genetic analyses and breeding approaches.