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Formins: linking cytoskeleton and endomembranes in plant cells.

Cvrčková F, Oulehlová D, Žárský V - Int J Mol Sci (2014)

Bottom Line: Moreover, some plant formins contain transmembrane domains and participate in anchoring cytoskeletal structures to the plasmalemma, and possibly to other membranes.Here we summarize the available evidence suggesting that formins participate in membrane trafficking and endomembrane, especially ER, organization also in plants.We propose that, despite some methodological pitfalls inherent to in vivo studies based on (over)expression of truncated and/or tagged proteins, formins are beginning to emerge as candidates for the so far somewhat elusive link between the plant cytoskeleton and the endomembrane system.

View Article: PubMed Central - PubMed

Affiliation: Department of Experimental Plant Biology, Faculty of Sciences, Charles University, Viničná 5, 128 43 Prague 2, Czech Republic. fatima@natur.cuni.cz.

ABSTRACT
The cytoskeleton plays a central part in spatial organization of the plant cytoplasm, including the endomebrane system. However, the mechanisms involved are so far only partially understood. Formins (FH2 proteins), a family of evolutionarily conserved proteins sharing the FH2 domain whose dimer can nucleate actin, mediate the co-ordination between actin and microtubule cytoskeletons in multiple eukaryotic lineages including plants. Moreover, some plant formins contain transmembrane domains and participate in anchoring cytoskeletal structures to the plasmalemma, and possibly to other membranes. Direct or indirect membrane association is well documented even for some fungal and metazoan formins lacking membrane insertion motifs, and FH2 proteins have been shown to associate with endomembranes and modulate their dynamics in both fungi and metazoans. Here we summarize the available evidence suggesting that formins participate in membrane trafficking and endomembrane, especially ER, organization also in plants. We propose that, despite some methodological pitfalls inherent to in vivo studies based on (over)expression of truncated and/or tagged proteins, formins are beginning to emerge as candidates for the so far somewhat elusive link between the plant cytoskeleton and the endomembrane system.

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Arabidopsis Class I formin AtFH5 (At5g54650) can associate with the nuclear membrane and ER in the epidermis of N. benthamiana leaves after Agrobacterium-mediated transient transformation with a plasmid carrying full length AtFH5 fused to the C end of GFP under the control of the 35S promoter. (a) Maximum projection of a stack of confocal images of epidermal cells expressing GFP:AtFH5, 5 days post-transformation; (b) Control cells expressing free GFP showing cytoplasmic and nuclear localization, 6 days post-transformation (maximum projection); (c) Detail of a cell expressing GFP:AtFH5, 4 days post transformation (maximum projection); and (d) Two optical sections of the cell presented in (c), showing localization in the nuclear membrane (top) and in the sub-cortical ER (bottom).
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ijms-16-00001-f002: Arabidopsis Class I formin AtFH5 (At5g54650) can associate with the nuclear membrane and ER in the epidermis of N. benthamiana leaves after Agrobacterium-mediated transient transformation with a plasmid carrying full length AtFH5 fused to the C end of GFP under the control of the 35S promoter. (a) Maximum projection of a stack of confocal images of epidermal cells expressing GFP:AtFH5, 5 days post-transformation; (b) Control cells expressing free GFP showing cytoplasmic and nuclear localization, 6 days post-transformation (maximum projection); (c) Detail of a cell expressing GFP:AtFH5, 4 days post transformation (maximum projection); and (d) Two optical sections of the cell presented in (c), showing localization in the nuclear membrane (top) and in the sub-cortical ER (bottom).

Mentions: Indeed, AtFH1, reported to accumulate in tobacco pollen tube plasmalemma upon ectopic heterologous overexpression, decorates also some intracytoplasmic structures under these conditions [83]. Remarkably, Arabidopsis mutants lacking AtFH1 exhibit impaired endocytosis, suggesting a direct or indirect participation of this formin in membrane trafficking [84]. AtFH5, which is naturally expressed in pollen, localizes both inside growing pollen tube tips and in their cortex when C-terminally GFP-tagged [85], and overexpression of GFP-tagged derivatives of the related pollen formin AtFH3 also resulted in a cytoplasmic signal [37]. Such observations suggest a possible association of at least a subpopulation of Class I formins with secretory or endocytotic pathway compartments. Indeed, fluorescent protein-tagged AtFH4 was upon closer observation found to localize to the cortical ER and participate in its co-alignment with microtubules [45], while AtFH8 was observed predominantly at the cell plates of dividing root cortex cells and at the nuclear envelope, with weaker signals either in the cytoplasm or the ER, although the quality of the published images does not allow distinguishing between these locations [47]. Localization to the nuclear membrane, and, to a lesser extent, the cortical ER, was also seen in Nicotiana benthamiana leaf epidermis transiently transformed using the p19 enhancer system [86] with constructs expressing N-terminally GFP-tagged AtFH5, i.e., a derivative of this formin that should not enter the secretory pathway ([87]; Figure 2). In this case, the fluorescent protein may become localized through interactions with other membrane proteins, including possibly dimerization with related endogenous formins.


Formins: linking cytoskeleton and endomembranes in plant cells.

Cvrčková F, Oulehlová D, Žárský V - Int J Mol Sci (2014)

Arabidopsis Class I formin AtFH5 (At5g54650) can associate with the nuclear membrane and ER in the epidermis of N. benthamiana leaves after Agrobacterium-mediated transient transformation with a plasmid carrying full length AtFH5 fused to the C end of GFP under the control of the 35S promoter. (a) Maximum projection of a stack of confocal images of epidermal cells expressing GFP:AtFH5, 5 days post-transformation; (b) Control cells expressing free GFP showing cytoplasmic and nuclear localization, 6 days post-transformation (maximum projection); (c) Detail of a cell expressing GFP:AtFH5, 4 days post transformation (maximum projection); and (d) Two optical sections of the cell presented in (c), showing localization in the nuclear membrane (top) and in the sub-cortical ER (bottom).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4307232&req=5

ijms-16-00001-f002: Arabidopsis Class I formin AtFH5 (At5g54650) can associate with the nuclear membrane and ER in the epidermis of N. benthamiana leaves after Agrobacterium-mediated transient transformation with a plasmid carrying full length AtFH5 fused to the C end of GFP under the control of the 35S promoter. (a) Maximum projection of a stack of confocal images of epidermal cells expressing GFP:AtFH5, 5 days post-transformation; (b) Control cells expressing free GFP showing cytoplasmic and nuclear localization, 6 days post-transformation (maximum projection); (c) Detail of a cell expressing GFP:AtFH5, 4 days post transformation (maximum projection); and (d) Two optical sections of the cell presented in (c), showing localization in the nuclear membrane (top) and in the sub-cortical ER (bottom).
Mentions: Indeed, AtFH1, reported to accumulate in tobacco pollen tube plasmalemma upon ectopic heterologous overexpression, decorates also some intracytoplasmic structures under these conditions [83]. Remarkably, Arabidopsis mutants lacking AtFH1 exhibit impaired endocytosis, suggesting a direct or indirect participation of this formin in membrane trafficking [84]. AtFH5, which is naturally expressed in pollen, localizes both inside growing pollen tube tips and in their cortex when C-terminally GFP-tagged [85], and overexpression of GFP-tagged derivatives of the related pollen formin AtFH3 also resulted in a cytoplasmic signal [37]. Such observations suggest a possible association of at least a subpopulation of Class I formins with secretory or endocytotic pathway compartments. Indeed, fluorescent protein-tagged AtFH4 was upon closer observation found to localize to the cortical ER and participate in its co-alignment with microtubules [45], while AtFH8 was observed predominantly at the cell plates of dividing root cortex cells and at the nuclear envelope, with weaker signals either in the cytoplasm or the ER, although the quality of the published images does not allow distinguishing between these locations [47]. Localization to the nuclear membrane, and, to a lesser extent, the cortical ER, was also seen in Nicotiana benthamiana leaf epidermis transiently transformed using the p19 enhancer system [86] with constructs expressing N-terminally GFP-tagged AtFH5, i.e., a derivative of this formin that should not enter the secretory pathway ([87]; Figure 2). In this case, the fluorescent protein may become localized through interactions with other membrane proteins, including possibly dimerization with related endogenous formins.

Bottom Line: Moreover, some plant formins contain transmembrane domains and participate in anchoring cytoskeletal structures to the plasmalemma, and possibly to other membranes.Here we summarize the available evidence suggesting that formins participate in membrane trafficking and endomembrane, especially ER, organization also in plants.We propose that, despite some methodological pitfalls inherent to in vivo studies based on (over)expression of truncated and/or tagged proteins, formins are beginning to emerge as candidates for the so far somewhat elusive link between the plant cytoskeleton and the endomembrane system.

View Article: PubMed Central - PubMed

Affiliation: Department of Experimental Plant Biology, Faculty of Sciences, Charles University, Viničná 5, 128 43 Prague 2, Czech Republic. fatima@natur.cuni.cz.

ABSTRACT
The cytoskeleton plays a central part in spatial organization of the plant cytoplasm, including the endomebrane system. However, the mechanisms involved are so far only partially understood. Formins (FH2 proteins), a family of evolutionarily conserved proteins sharing the FH2 domain whose dimer can nucleate actin, mediate the co-ordination between actin and microtubule cytoskeletons in multiple eukaryotic lineages including plants. Moreover, some plant formins contain transmembrane domains and participate in anchoring cytoskeletal structures to the plasmalemma, and possibly to other membranes. Direct or indirect membrane association is well documented even for some fungal and metazoan formins lacking membrane insertion motifs, and FH2 proteins have been shown to associate with endomembranes and modulate their dynamics in both fungi and metazoans. Here we summarize the available evidence suggesting that formins participate in membrane trafficking and endomembrane, especially ER, organization also in plants. We propose that, despite some methodological pitfalls inherent to in vivo studies based on (over)expression of truncated and/or tagged proteins, formins are beginning to emerge as candidates for the so far somewhat elusive link between the plant cytoskeleton and the endomembrane system.

Show MeSH
Related in: MedlinePlus