Cloning and characterization of ZmPIP1-5b, an aquaporin transporting water and urea

A cDNA, ZmPIP1-5b, isolated from a nitrate-treated maize roots cDNA library has 95.2% sequence identity to ZmPIP1-5. However, sequence divergences are not uniformly distributed, but are mainly observed in 3' and 5' non-coding regions (82.7 and 77.3%, respectively). The coding regions differ by two nucleotides over 864, but ZmPIP1-5b and ZmPIP1-5 encode identical proteins. The deduced ZmPIP1-5 protein is 288 amino acids in length, contains six putative transmembrane domains and the MIP signature NPA. ZmPIP1-5, like other proteins belonging to PIPI subfamily, has a low aquaporin activity when expressed in Xenopus oocytes. However, a special feature of ZmPIP1-5, when compared with other plant PIPs, is its capacity to transport urea. ZmPIP1-5 is preferentially expressed in roots and addition of KNO3 to previously nitrogen-starved maize plants induced the transcript level of this gene. Further-more, ZmPIP1-5 expression oscillated during the day-night cycle. In situ hybridization showed that this regulation is tissue specific. Modulation of ZmPIP1-5 expression by KNO3 and during the day-night cycle is discussed in regards to root water permeability changes, (C) 2003 Elsevier Science Ireland Ltd. All rights reserved.