Molecular cloning of a novel water channel from rice: its products expression in Xenopus oocytes and involvement in chilling tolerance.

Water channel proteins, aquaporins, play a fundamental role in transmembrane water movements in plants. We isolated rice cDNA, rwc1, by screening a rice (Oryza sativa cv. Josaeng Tongil) cDNA library using a conserved motif of aquaporins. Like other aquaporin genes, rwc1 encodes a 290-residue protein with six putative transmembrane domains. The derived amino acid sequence of RWC1 shows high homology with PIP1 (plasma membrane intrinsic protein 1) subfamily members, which suggest it is localized in the plasma membrane. Injection of its cRNA into Xenopus oocytes increased the osmotic water permeability of the oocytes 2-3 times. Northern analysis showed that rice aquaporin genes are expressed in rice seedling leaves and roots, but that it disappeared from the root 6 h after osmotic stress began and that the transcript level remained low for about 24 h, then recovered. The time course of rice aquaporin gene-expression under osmotic stress was correlated with time course of turgor transition in plant. On the other hand, the levels of rice aquaporin gene-transcripts in leaves under chilling and recovery temperature depend on the pretreatment of mannitol for short time. This variation of the transcripts shown that rice aquaporin genes may play an important role in response to water stress-induced chilling tolerance.