Interaction of hormonal and two component signaling pathways - regulatory modules determining differentiation of transfer tissues in barley

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Assimilate supply to reproductive organs has a major impact on yield in cereal crops like barley by affecting grain number and grain size. The development of spikelets/florets and grains is associated with differentiation of vascular bundles in spikes and grains and establishment of distinct transfer tissues for nutrient uptake in filial grain organs, particularly the endosperm. Understanding the molecular basis and regulatory networks triggering differentiation of transfer tissues is a prerequisite for improvement of yield potential. Tissue-specific 454 and Illumina sequencing unexpectedly identified two-component signaling (TCS) phosphorelays as major signal transduction pathway in differentiating endosperm transfer cells (ETCs) of barley. ETC-specific co-expression modules of TCS elements and confirmed protein interactions pinpoint to a participation of signaling elements in distinct phosphorelays. Hormone-dependent transcriptional activation and correlative data revealed a crosstalk of ABA/ethylene and TCS phosphorelays during ETC differentiation. RNAi-lines with strongly reduced histidine kinase (HvHK1) transcript amounts showed poorly differentiated cells in the central ETC region, missing characteristic cell wall ingrowths and smaller grains with strongly reduced starch accumulation. RNA-seq of the developing ETC region is planned to elucidate HvHK1-dependent pathways and regulatory networks. TALEN-induced gene modification of the type-C response regulator HvRR15 and/or gene copies induced a strong endosperm-specific phenotype with a prominent disruption of the central endosperm and abnormal aleurone differentiation in the wing region. Further histological observation and molecular analysis will refine the exciting phenotype. Comprehensive tissue-specific expression analysis revealed further candidate TCS genes preferentially expressed in the vasculature of spikes and grains. Knock-out of candidates by the newly developed CRISPR/CAS9-technology will decipher the function in planta.