AUTHOR=Holubová Katarína , Hensel Goetz , Vojta Petr , Tarkowski Petr , Bergougnoux Véronique , Galuszka Petr 

TITLE=Modification of Barley Plant Productivity Through Regulation of Cytokinin Content by Reverse-Genetics Approaches

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 9 - 2018

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01676

DOI=10.3389/fpls.2018.01676

ISSN=1664-462X

ABSTRACT=Barley is one of the most important cereals, which is used for breweries, animal and human feeds. Genetic manipulation of plant hormone cytokinin (CK) levels may influence several physiological processes, besides others stress tolerance, root formation and crop yield. In planta, endogenous CK status is finely regulated by the enzyme cytokinin dehydrogenase (EC 1.5.99.12; CKX), that irreversibly cleaves the N6-side chain of adenine-derived CKs. Increasing grain yield by mean of manipulation of endogenous CK content was assayed by the silencing of the HvCKX1 gene. Moreover, to elucidate the putative role of HvCKX1 gene on grain production, knocked-out Hvckx1 mutant plants were generated using RNA-guided Cas9 system.
Homozygote transgenic plants with silenced HvCKX1 gene and azygous knock-out Hvckx1 mutants have been selected and analysed. Both reduced expression of HvCKX1 gene and CKX activity were measured in different stages of barley grain development. Phenotyping of the transgenic lines revealed reduced root growth, however plants produced more tillers and grains than azygous wild-type controls and the total yield was increased up to 15 per cent. Although plant productivity was increased, biomass of one grain was decreased to 80% of wild-type grains. RNA-seq analysis of knock-down transgenic lines revealed that several important macronutrient transporters were downregulated in stage of massive starch accumulation. It suggests that local accumulation of CKs negatively affected nutrients flow resulting in reduced grain biomass. Obtained results confirmed the key role of HvCKX1 gene for regulation of CK content in barley.