Genome-wide characterization of two-component system elements in barley enables the identification of grain-specific...

The two-component system (TCS) serves as a common intracellular signal transduction pathway implicated in various processes of plant development and response to abiotic stress. With regard to the important cereal crop barley, only partial information about the occurrence of TCS signaling elements in the genome and putative functions is available.

In this study, we identified a total of 67 non-redundant TCS genes from all subgroups of the phosphorelay in the latest barley reference genome. Functional annotation and phylogenetic characterization was combined with a comprehensive gene expression analysis of the signaling components. Expression profiles hint at potential functions in vegetative and reproductive organs and tissue types as well as diverse stress responses. Apparently, a distinct subset of TCS genes revealed a stringent grain-specificity not being expressed elsewhere in the plant. By using laser capture microdissection (LCM)-based transcript analysis of barley grain tissues, we refined expression profiles of selected TCS genes and attributed them to individual cell types within the grain. Distinct TCS elements are exclusively expressed in the different maternal and filial cell types, particularly in the endosperm transfer cell (ETC) region. These genes are deemed to be selected in the domestication process of modern cultivars. Moreover, barley plants transformed with a synthetic sensor (TCSn::GFP) showed a high and specific activity in the ETC region of grains monitoring transcriptional output of the signaling system.

The results provide comprehensive insights into the TCS gene family in the temperate cereal crop barley and indicate implications in various agronomic traits. The dataset is valuable for future research in different aspects of plant development and will be indispensable not only for barley, but also for other crops of the Poaceae.