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

Abstract 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 PIP1 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 KNO 3 to previously nitrogen-starved maize plants induced the transcript level of this gene. Furthermore, 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 KNO 3 and during the day–night cycle is discussed in regards to root water permeability changes.