Abstract
Four full-length cDNAs of plasma membrane intrinsic proteins (PIPs) were systematically isolated, identified and cloned from tulip (Tulipa gesneriana) petals According to the nomenclature of plant aquaporins, these were designated TgPIP1;1, TgPIP1;2, TgPIP2;1 and TgPIP2;2. Of these four homologues, only TgPIP2;2 displayed the significant water channel activity (Wa) in the Xenopus oocytes heterologous expression system. However, in Pichia pastoris expression system, both TgPIP2;1 and TgPIP2;2 showed Wa. The Wa was affected by mercury and inhibitors of protein kinases and protein phosphatases. Site-directed mutagenesis approache and spheroplast bursting assay revealed that Ser-35, Ser-116 and Ser-274 were the putative phosphorylation sites of the TgPIP2;2. Real-time RT-PCR analysis revealed that TgPIP2;2 is ubiquitously expressed in all organs. Collected data suggest that TgPIP2;2 might be modulated by phosphorylation and dephosphorylation for regulating water channel activity, and may play role in transcellular water transport in all tulip organs.
