Fetter Karolina, Van Wilder Valérie, Moshelion Menachem, Chaumont François
Unité de Biochimie Physiologique, Institut des Science de la Vie, Université Catholique de Louvain, Croix du Sud 2-20, B-1348 Louvain-la-Neuve, Belgium.
Plant Cell. 2004 Jan;16(1):215-28. doi: 10.1105/tpc.017194. Epub 2003 Dec 11.
Plant plasma membrane intrinsic proteins (PIPs) cluster in two evolutionary subgroups, PIP1 and PIP2, with different aquaporin activities when expressed in Xenopus oocytes. Maize ZmPIP1;1 and ZmPIP1;2 do not increase the osmotic water permeability coefficient (Pf), whereas ZmPIP2;1, ZmPIP2;4, and ZmPIP2;5 do. Here, we show that coexpression of the nonfunctional ZmPIP1;2 and the functional ZmPIP2;1, ZmPIP2;4, or ZmPIP2;5 resulted in an increase in Pf that was dependent on the amount of injected ZmPIP1;2 complementary RNA. Confocal analysis of oocytes expressing ZmPIP1;2-green fluorescent protein (GFP) alone or ZmPIP1;2-GFP plus ZmPIP2;5 showed that the amount of ZmPIP1;2-GFP present in the plasma membrane was significantly greater in coexpressing cells. Nickel affinity chromatography purification of ZmPIP2;1 fused to a His tag coeluted with ZmPIP1;2-GFP demonstrated physical interaction and heteromerization of both isoforms. Interestingly, coexpression of ZmPIP1;1 and ZmPIP2;5 did not result in a greater increase in Pf than did the expression of ZmPIP2;5 alone, but coexpression of the ZmPIP1;1 and ZmPIP1;2 isoforms induced a Pf increase, indicating that PIP1 isoform heteromerization is required for both of them to act as functional water channels. Mutational analysis demonstrated the important role of the C-terminal part of loop E in PIP interaction and water channel activity induction. This study has revealed a new mechanism of plant aquaporin regulation that might be important in plant water relations.
植物质膜内在蛋白（PIPs）可分为两个进化亚组，即PIP1和PIP2，当它们在非洲爪蟾卵母细胞中表达时，具有不同的水通道蛋白活性。玉米ZmPIP1;1和ZmPIP1;2不会增加渗透水通透系数（Pf），而ZmPIP2;1、ZmPIP2;4和ZmPIP2;5会增加。在此，我们表明，无功能的ZmPIP1;2与有功能的ZmPIP2;1、ZmPIP2;4或ZmPIP2;5共表达会导致Pf增加，且这种增加依赖于注射的ZmPIP1;2互补RNA的量。对单独表达ZmPIP1;2 - 绿色荧光蛋白（GFP）或ZmPIP1;2 - GFP加ZmPIP2;5的卵母细胞进行共聚焦分析表明，共表达细胞中质膜上存在的ZmPIP1;2 - GFP量显著更多。镍亲和层析纯化与His标签融合的ZmPIP2;1时，它与ZmPIP1;2 - GFP共洗脱，证明了这两种亚型之间存在物理相互作用和异源二聚化。有趣的是，ZmPIP1;1和ZmPIP2;5共表达导致的Pf增加并不比单独表达ZmPIP2;5时更大，但ZmPIP1;1和ZmPIP1;2亚型共表达会诱导Pf增加，这表明PIP1亚型异源二聚化是它们两者作为功能性水通道发挥作用所必需的。突变分析表明，环E的C末端部分在PIP相互作用和水通道活性诱导中起重要作用。这项研究揭示了一种新的植物水通道蛋白调节机制，这可能对植物水分关系很重要。
