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-b-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.
Tight regulation of plant actin cytoskeleton organization and dynamics is crucial for numerous cellular processes including cell division, expansion and intracellular trafficking. Among the various actin regulatory proteins, actin-bundling proteins trigger the formation of bundles composed of several parallel actin filaments closely packed together. Actin bundles are present in virtually all plant cells, but their biological roles have rarely been addressed directly. However, decades of research in the plant cytoskeleton field yielded a bulk of data from which an overall picture of the functions supplied by actin bundles in plant cells emerges. Although plants lack several equivalents of animal actin-bundling proteins, they do possess major bundler classes including fimbrins, villins and formins. The existence of additional players is not excluded as exemplified by the recent characterization of plant LIM proteins, which trigger the formation of actin bundles both in vitro and in vivo. This apparent functional redundancy likely reflects the need for plant cells to engineer different types of bundles that act at different sub-cellular locations and exhibit specific function-related properties. By surveying information regarding the properties of plant actin bundles and their associated bundling proteins, the present review aims at clarifying why and how plants make actin bundles. Cell Motil. Cytoskeleton 66: 940-957, 2009. '
Background:Elongator is an acetylase complex that regulates cell migration. Results: DERP6 (ELP5) and C3ORF75 (ELP6) are characterized as Elongator subunits that control cell motility and tumorigenicity of melanoma cells. ELP5 ensures Elongator integrity by connecting ELP3 to ELP4. Conclusion: ELP5 and ELP6 are new players for migration and tumorigenicity of transformed cells. Significance: Elongator may be involved in both tumor initiation and progression.
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