Pih K T, Kabilan V, Lim J H, Kang S G, Piao H L, Jin J B, Hwang I
Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Chinju, Korea.
Mol Cells. 1999 Feb 28;9(1):84-90.
Aquaporins, small channel proteins, found in a variety of organisms are members of the major intrinsic protein (MIP) superfamily and have been shown to facilitate water transport when expressed in Xenopus oocytes. We isolated two Arabidopsis cDNAs, SIMIP and SITIP, that encode protein homologues of the MIP superfamily. SIMIP exhibits a high degree of sequence homology to PIP3 and MIP1, and thus may belong to the plasmamembrane intrinsic protein (PIP) subfamily, whereas salt-stress inducible tonoplast intrinsic protein (SITIP) is highly homologous to VM23 and gamma-TIP, and therefore may belong to the TIP subfamily. Expression studies revealed that the two genes showed a different expression pattern. The SIMIP gene was expressed in a tissue-specific manner, for example, its highest transcript level is found in flowers, relatively low levels in siliques, and very low level in leaves and roots. In contrast, SITIP was expressed in nearly equal amounts in all the tissues we examined. Also, the expression of SIMIP and SITIP showed a temporal regulation pattern. For example, the highest expression level was at 1 week after germination. In addition, the transcript levels of SIMIP and SMTIP were increased upon NaCl and ABA treatments. The biological function of the 2 genes were investigated using two NaCl stress-sensitive yeast mutant strains. The mutant yeast cells expressing these 2 genes were more resistant to high NaCl conditions. The results suggest that the proteins encoded by these genes may be involved in the osmoregulation in plants under high osmotic stress such as under a high salt condition.
水通道蛋白是一类存在于多种生物体中的小通道蛋白，属于主要内在蛋白（MIP）超家族。研究表明，当在非洲爪蟾卵母细胞中表达时，水通道蛋白能够促进水的运输。我们从拟南芥中分离出两个cDNA，即SIMIP和SITIP，它们编码MIP超家族的蛋白同源物。SIMIP与PIP3和MIP1具有高度的序列同源性，因此可能属于质膜内在蛋白（PIP）亚家族；而盐胁迫诱导的液泡膜内在蛋白（SITIP）与VM23和γ-TIP高度同源，因此可能属于TIP亚家族。表达研究表明，这两个基因呈现出不同的表达模式。SIMIP基因以组织特异性的方式表达，例如，其转录本水平在花中最高，在角果中相对较低，在叶和根中非常低。相比之下，SITIP在我们检测的所有组织中的表达量几乎相等。此外，SIMIP和SITIP的表达呈现出时间调控模式。例如，在萌发后1周时表达水平最高。另外，经NaCl和ABA处理后，SIMIP和SMTIP的转录本水平升高。我们使用两种对NaCl胁迫敏感的酵母突变菌株研究了这两个基因的生物学功能。表达这两个基因的突变酵母细胞对高NaCl条件具有更强的抗性。结果表明，这些基因编码的蛋白质可能参与植物在高渗透胁迫（如高盐条件）下的渗透调节。
