Cytokinin plant hormones have been shown to play an important role in plant response to abiotic stresses. Herein, we expand upon the findings of Pospíšilová et al. [30] regarding preparation of novel transgenic barley lines overexpressing cytokinin dehydrogenase 1 gene from Arabidopsis under the control of mild root-specific promotor of maize β-glycosidase. These lines showed drought-tolerant phenotype mainly due to alteration of root architecture and stronger lignification of root tissue. A detailed transcriptomic analysis of roots of transgenic plants subjected to revitalization after drought stress revealed attenuated response through the HvHK3 cytokinin receptor and up-regulation of two transcription factors implicated in stress responses and abscisic acid sensitivity. Increased expression of several genes involved in the phenylpropanoid pathway as well as of genes encoding arogenate dehydratase/lyase participating in phenylalanine synthesis was found in roots during revitalization. Although more precursors of lignin synthesis were present in roots after drought stress, final lignin accumulation did not change compared to that in plants grown under optimal conditions. Changes in transcriptome indicated a higher auxin turnover in transgenic roots. The same analysis in leaves revealed that genes encoding putative enzymes responsible for production of jasmonates and other volatile compounds were up-regulated. Although transgenic barley leaves showed lower chlorophyll content and down-regulation of genes encoding proteins involved in photosynthesis than did wild-type plants when cultivated under optimal conditions, they did show a tendency to return to initial photochemical activities faster than did wild-type leaves when re-watered after severe drought stress. In contrast to optimal conditions, comparative transcriptomic analysis of revitalized leaves displayed up-regulation of genes encoding enzymes and proteins involved in photosynthesis, and especially those encoded by the chloroplast genome. Taken together, our results indicate that the partial cytokinin insensitivity induced in barley overexpressing cytokinin dehydrogenase contributes to tolerance to drought stress.

Department of Biophysics Centre of the Region Haná for Biotechnological and Agricultural Research Faculty of Science Palacký University in Olomouc Šlechtitelů 27 783 71 Olomouc Czech Republic

Department of Chemical Biology and Genetics Centre of the Region Haná for Biotechnological and Agricultural Research Faculty of Science Palacký University in Olomouc Šlechtitelů 27 783 71 Olomouc Czech Republic

Department of Molecular Biology Centre of the Region Haná for Biotechnological and Agricultural Research Faculty of Science Palacký University in Olomouc Šlechtitelů 27 783 71 Olomouc Czech Republic

Department of Molecular Biology Centre of the Region Haná for Biotechnological and Agricultural Research Faculty of Science Palacký University in Olomouc Šlechtitelů 27 783 71 Olomouc Czech Republic; Institute of Molecular and Translational Medicine Faculty of Medicine and Dentistry Palacký University in Olomouc Hněvotínská 1333 5 779 00 Olomouc Czech Republic

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