Members of the ran family of stress-inducible small GTP-binding proteins are differentially regulated in sweetpotato plants

Ran is a small GTP-binding protein that binds and subsequently hydrolyzes GTP. The functions of Ran in nuclear transport and mitotic progression are well conserved in plants and animals. In animal cells, stress treatments cause Ran relocalization and slowing of nuclear transport, but the role of Ran proteins in plant cells exposed to stress is still unclear. We have therefore compared Ran genes from three EST libraries construed from different cell types of sweetpotato and the distribution pattern of Ran ESTs differed according to cell type. We further characterized two IbRan genes. IbRan1 is a specific EST to the suspension cells and leaf libraries, and IbRan2 is specific EST to the root library. IbRan1 showed 94.6 % identity with IbRan2 at the amino acid level, but the C-terminal region of IbRan1 differed from that of IbRan2. These two genes showed tissue-specific differential regulation in wounded tissues. Chilling stress induced a similar expression pattern in both IbRan genes in the leaves and petioles, but they were differently regulated in the roots. Hydrogen peroxide treatment highly stimulated IbRan2 mRNA expression in the leaves and petioles, but had no significant effect on IbRan1 gene expression. These results showed that the transcription of these two IbRan genes responds differentially to abiotic stresses and that they are subjected to tissue-specific regulation. Plant Ran-type small G-proteins are a multigenic family, and the characterization of each Ran genes under various environmental stresses will contribute toward our understanding of the distinctive function of each plant Ran isoform.