Nuclear Export of Proteins and RNA Merkle, Thomas Merkle Thomas Several nuclear export receptors that facilitate the export of proteins and small RNAs from the nucleus to the cytoplasm have been functionally characterized in Arabidopsis thaliana in the past few years. With the specific cargo molecules they transport, the export receptors supply the cytoplasm with information, resulting in changes in cellular events. In this way, nuclear export receptors contribute to signal transduction that is highlighted in mutants with impaired export activity. In addition, nuclear export of proteins is part of a control layer for gene expression that is unique to eukaryotes, namely nucleocytoplasmic partitioning of regulatory proteins. This is revealed by growing evidence for shuttling proteins that participate in different signaling cascades, including phytohormone signaling. Although a plant mRNA export receptor is still missing in plants, several genes encoding protein factors that function in mRNA export to the cytoplasm were characterized by their mutant phenotypes. These findings show that cold, stress, or phytohormone signaling cascades and the control of flowering are especially sensitive to impaired mRNA biogenesis and export. 14 55-57 55-57 Springer 2009