Abstract
Hydrotropism is a response by which roots sense moisture gradient and induce a directional growth toward higher moisture area. We have previously identified an ahydrotropic Arabidopsis mutant, miz1, resulting from a point mutation at coding sequence of a gene encoding an uncharacterized protein. To elucidate the molecular function of MIZ1 protein in hydrotropism, we analyzed the localization of MIZ1 in Arabidopsis root cells. Several algorisms for prediction of protein localization indicated that MIZ1 localize to plastid. In addition, hydropathy analysis indicated that MIZ1 is soluble protein. Despite the prediction, the emission of GFP-tagged MIZ1 (MIZ1-GFP) in root cells of a transgenic Arabidopsis plant was not found in plastids. Interestingly, immunoblot analysis showed that MIZ1-GFP was detected not only in soluble protein fraction, but also in membrane fraction. Sucrose density gradient centrifugation method and protease protection assay showed that MIZ1-GFP is associated with the cytosolic side on endoplasmic reticulum membrane, suggesting MIZ1 is involved in a function related to ER. We need further investigation of ER function in hydrotropism to clarify the role of MIZ1.
