Expression of Plasma Membrane Water Channel Genes under Water Stress in Nicotiana excelsior

Deduced amino acid sequences encoded by the cDNAs related to the MIP gene family from Nicotiana excelsior were characterized. Phylogenetic characterization of the products of corresponding genes named NeMipl, NeMip2, and NeMip3 strongly suggested that they are water channel proteins localized in the plasma membrane. Organ specificity of the gene expression was examined in leaves, roots, and reproductive organs. NeMipl was expressed in roots and reproductive organs; however, it was hardly detectable in leaves. Two other genes, NeMip2 and NeMip3, were expressed in all of organs examined. mRNA accumulation from the genes was investigated in leaves under salt- and drought-stresses. The results demonstrated that mRNA accumulation from all three genes increased under salt- and drought-stresses within one day. However, they showed different accumulation patterns. In addition to their up-regulation under salt- and drought-stresses, daily changes in NeMip2 and NeMip3 mRNA accumulation was observed under unstressed conditions in leaves.