Silencing of the HvCKX1 gene decreases the cytokinin oxidase/dehydrogenase level in barley and leads to higher plant productivity

Stable RNA interference-based technology was used to silence the expression of the HvCKX1 gene in barley and the TaCKX1 gene in wheat and triticale. The silencing cassettes containing the fragments of these genes in the sense and antisense orientations were cloned into the pMCG161 binary vector and used for Agrobacterium-based transformation. Out of the five cultivars representing the three studied species, transgenic plants were obtained from one barley cultivar Golden Promise, one wheat cultivar Kontesa, and one triticale cultivar Wanad. Almost 80% of 52 regenerated lines of Golden Promise exhibited significantly decreased cytokinin oxidase/dehydrogenase (CKX) enzyme activity in bulked samples of their T-1 roots. There was a positive correlation between the enzyme activity and the plant productivity, expressed as the yield, the number of seeds per plant, and the 1000 grain weight. Additionally, these traits were associated with a greater root mass. Lower CKX activity led to a higher plant yield and root weight. This higher plant productivity and altered plant architecture were maintained in a population of segregating T-1 plants. The levels of HvCKX1 transcript accumulation were measured in various tissues of Golden Promise and Scarlett non-transgenic barley plants in order to choose the most appropriate plant organs to study the expression and/or silencing of the gene in those transgenic lines. The highest levels of the HvCKX1 transcript were detected in spikes 0 days after pollination (0 DAP), 7 DAP, and 14 DAP, and in the seedling roots. The analysis of HvCKX1 gene expression and CKX enzyme activity and the evaluation of the phenotype were performed in the progeny of seven selected transgenic T-1 lines. The relative expression of HvCKX1 measured in the spikes 0 DAP and 14 DAP, respectively, ranged from 0.52 +/- 0.04 to 1.15 +/- 0.26 and from 0.47 +/- 0.07 to 0.89 +/- 0.15. The lowest relative values were obtained for the enzyme activity in the spikes at 0 DAP, which ranged from 0.15 +/- 0.02 to 1.05 +/- 0.14 per single progeny plant. Based on these three values, the coefficient of HvCKX1 silencing in the spikes was estimated. Possible mechanisms leading to higher plant productivity via the silencing of HvCKX1 and a decrease in CKX enzyme activity are discussed.