Fluorescent reporter lines for auxin and cytokinin signalling in barley ( Hordeum vulgare )

The phytohormones auxin and cytokinin influence the development and maintenance of plant stem cell niches. Although barley ( Hordeum vulgare ) is the fourth most abundant cereal crop plant, the knowledge about these important phytohormones in regard to the root and shoot stem cell niche in barley is still negligible. In this study, we analyse the influence of auxin and cytokinin on the barley root meristem and present reporter lines to describe the auxin and cytokinin signalling output. Application of high concentrations of auxin and cytokinin to barley seedlings had a negative influence on barley root and meristem growth. The expression of the cytokinin reporter TCSn revealed that cytokinin signalling mostly takes place in the stele cells proximal to the QC and in the differentiated root cap cells, but can additionally be activated in the root stem cell niche by cytokinin application. Analysing signalling targets of auxin showed that a homologue of AtPLT1, HvPLT1, is expressed in a similar way as AtPLT1 in Arabidopsis , in particular in the QC and the surrounding cells. Furthermore, a homologue of the auxin PIN transporters PIN1, HvPIN1, was expressed in the root and the shoot meristem and polarly localizes to the plasma membrane. Its expression is regulated by cytokinin and the intracellular localisation is affected by BFA. With this study, we provide a valuable tool set of fluorescent barley reporter lines for auxin and cytokinin.