Centre de Recherche Public-Santé, L-1526 Luxembourg, Luxembourg.
Plant Cell. 2010 Sep;22(9):3034-52. doi: 10.1105/tpc.110.075960. Epub 2010 Sep 3.
Recently, a number of two LIM-domain containing proteins (LIMs) have been reported to trigger the formation of actin bundles, a major higher-order cytoskeletal assembly. Here, we analyzed the six Arabidopsis thaliana LIM proteins. Promoter-β-glucuronidase reporter studies revealed that WLIM1, WLIM2a, and WLIM2b are widely expressed, whereas PLIM2a, PLIM2b, and PLIM2c are predominantly expressed in pollen. LIM-green fluorescent protein (GFP) fusions all decorated the actin cytoskeleton and increased actin bundle thickness in transgenic plants and in vitro, although with different affinities and efficiencies. Remarkably, the activities of WLIMs were calcium and pH independent, whereas those of PLIMs were inhibited by high pH and, in the case of PLIM2c, by high [Ca(2+)]. Domain analysis showed that the C-terminal domain is key for the responsiveness of PLIM2c to pH and calcium. Regulation of LIM by pH was further analyzed in vivo by tracking GFP-WLIM1 and GFP-PLIM2c during intracellular pH modifications. Cytoplasmic alkalinization specifically promoted release of GFP-PLIM2c but not GFP-WLIM1, from filamentous actin. Consistent with these data, GFP-PLIM2c decorated long actin bundles in the pollen tube shank, a region of relatively low pH. Together, our data support a prominent role of Arabidopsis LIM proteins in the regulation of actin cytoskeleton organization and dynamics in sporophytic tissues and pollen.
最近，有一些双 LIM 结构域蛋白（LIMs）被报道可以触发肌动蛋白束的形成，这是一种主要的高级细胞骨架组装。在这里，我们分析了六个拟南芥的 LIM 蛋白。启动子-β-葡萄糖醛酸酶报告基因研究表明，WLIM1、WLIM2a 和 WLIM2b 广泛表达，而 PLIM2a、PLIM2b 和 PLIM2c 主要在花粉中表达。LIM-绿色荧光蛋白（GFP）融合蛋白都在转基因植物和体外中装饰肌动蛋白细胞骨架并增加肌动蛋白束的厚度，尽管亲和力和效率不同。值得注意的是，WLIMs 的活性不受钙和 pH 的影响，而 PLIMs 的活性受高 pH 抑制，PLIM2c 的活性还受高[Ca(2+)]抑制。结构域分析表明，C 端结构域是 PLIM2c 对 pH 和钙响应的关键。通过在细胞内 pH 变化过程中跟踪 GFP-WLIM1 和 GFP-PLIM2c，进一步在体内分析了 LIM 的调节。细胞质碱化特异性促进 GFP-PLIM2c 从丝状肌动蛋白中释放，但 GFP-WLIM1 不会释放。与这些数据一致的是，GFP-PLIM2c 装饰花粉管柄中的长肌动蛋白束，花粉管柄是一个 pH 值相对较低的区域。总的来说，我们的数据支持拟南芥 LIM 蛋白在调节孢子组织和花粉中肌动蛋白细胞骨架组织和动力学中的重要作用。
