Gibbon B C, Zonia L E, Kovar D R, Hussey P J, Staiger C J
Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
Plant Cell. 1998 Jun;10(6):981-93. doi: 10.1105/tpc.10.6.981.
The actin binding protein profilin has dramatic effects on actin polymerization in vitro and in living cells. Plants have large multigene families encoding profilins, and many cells or tissues can express multiple profilin isoforms. Recently, we characterized several profilin isoforms from maize pollen for their ability to alter cytoarchitecture when microinjected into living plant cells and for their association with poly-L-proline and monomeric actin from maize pollen. In this study, we characterize a new profilin isoform from maize, which has been designated ZmPRO4, that is expressed predominantly in endosperm but is also found at low levels in all tissues examined, including mature and germinated pollen. The affinity of ZmPRO4 for monomeric actin, which was measured by two independent methods, is similar to that of the three profilin isoforms previously identified in pollen. In contrast, the affinity of ZmPRO4 for poly-L-proline is nearly twofold higher than that of native pollen profilin and the other recombinant profilin isoforms. When ZmPRO4 was microinjected into plant cells, the effect on actin-dependent nuclear position was significantly more rapid than that of another pollen profilin isoform, ZmPRO1. A gain-of-function mutant (ZmPRO1-Y6F) was created and found to enhance poly-L-proline binding activity and to disrupt cytoarchitecture as effectively as ZmPRO4. In this study, we demonstrate that profilin isoforms expressed in a single cell can have different effects on actin in living cells and that the poly-L-proline binding function of profilin may have important consequences for the regulation of actin cytoskeletal dynamics in plant cells.
肌动蛋白结合蛋白切丝蛋白在体外和活细胞中对肌动蛋白聚合具有显著影响。植物拥有编码切丝蛋白的大型多基因家族，许多细胞或组织能够表达多种切丝蛋白异构体。最近，我们对来自玉米花粉的几种切丝蛋白异构体进行了表征，检测了它们显微注射到活植物细胞中时改变细胞结构的能力，以及它们与来自玉米花粉的聚-L-脯氨酸和单体肌动蛋白的结合情况。在本研究中，我们表征了一种来自玉米的新切丝蛋白异构体，命名为ZmPRO4，它主要在胚乳中表达，但在所有检测的组织中也有低水平表达，包括成熟花粉和萌发花粉。通过两种独立方法测定，ZmPRO4对单体肌动蛋白的亲和力与之前在花粉中鉴定出的三种切丝蛋白异构体相似。相比之下，ZmPRO4对聚-L-脯氨酸的亲和力比天然花粉切丝蛋白和其他重组切丝蛋白异构体高出近两倍。当将ZmPRO4显微注射到植物细胞中时，对肌动蛋白依赖性核位置的影响比另一种花粉切丝蛋白异构体ZmPRO1显著更快。构建了一个功能获得性突变体（ZmPRO1-Y6F），发现其增强了聚-L-脯氨酸结合活性，并与ZmPRO4一样有效地破坏细胞结构。在本研究中，我们证明在单个细胞中表达的切丝蛋白异构体对活细胞中的肌动蛋白可能有不同影响，并且切丝蛋白的聚-L-脯氨酸结合功能可能对植物细胞中肌动蛋白细胞骨架动力学的调节具有重要意义。
