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A cytoplasm-specific activity encoded by the Trithorax-like ATX1 gene.

Ndamukong I, Lapko H, Cerny RL, Avramova Z - Nucleic Acids Res. (2011)

Bottom Line: It is encoded from an internal promoter in the ATX1 locus as an isoform containing only the SET domain (soloSET).It is located exclusively in the cytoplasm and its substrate is the elongation factor 1A (EF1A).Loss of SET, but not of the histone modifying ATX1-SET activity, affects cytoskeletal actin bundling illustrating that the two isoforms have distinct functions in Arabidopsis cells.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, USA.

ABSTRACT
Eukaryotes produce multiple products from a single gene locus by alternative splicing, translation or promoter usage as mechanisms expanding the complexity of their proteome. Trithorax proteins, including the Arabidopsis Trithorax-like protein ATX1, are histone modifiers regulating gene activity. Here, we report that a novel member of the Trithorax family has a role unrelated to chromatin. It is encoded from an internal promoter in the ATX1 locus as an isoform containing only the SET domain (soloSET). It is located exclusively in the cytoplasm and its substrate is the elongation factor 1A (EF1A). Loss of SET, but not of the histone modifying ATX1-SET activity, affects cytoskeletal actin bundling illustrating that the two isoforms have distinct functions in Arabidopsis cells.

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Cytoplasmic localization of soloSET and transgenic plants expressing RNAi-SET. (a) Transiently expressed GFP-soloSET fusion protein in tobacco leaf cells is detected only in cytoplasm. Arrows point to perinuclearly localized green signal. (b) Nuclearly localized full-size ATX1-GFP fusion protein is shown for comparison. Chloroplasts are shown in red (chlorophyll autoflorescence). Bars are 20 µm. (c) transgenic Arabidopsis plants expressing RNAi-SET showing precocious flowering (at the stage of only four true leaves), chlorosis in sepals and inflorescences, and a flower with abnormal short stamen (arrowhead) and asymmetric petals (arrows).
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Figure 2: Cytoplasmic localization of soloSET and transgenic plants expressing RNAi-SET. (a) Transiently expressed GFP-soloSET fusion protein in tobacco leaf cells is detected only in cytoplasm. Arrows point to perinuclearly localized green signal. (b) Nuclearly localized full-size ATX1-GFP fusion protein is shown for comparison. Chloroplasts are shown in red (chlorophyll autoflorescence). Bars are 20 µm. (c) transgenic Arabidopsis plants expressing RNAi-SET showing precocious flowering (at the stage of only four true leaves), chlorosis in sepals and inflorescences, and a flower with abnormal short stamen (arrowhead) and asymmetric petals (arrows).

Mentions: Transient expression of a soloSET-GFP fusion protein in tobacco leaf cells revealed that it was present only in the cytoplasm (Figure 2a). This is in contrast to ATX1-GFP, which localizes in the nucleus (Figure 2b) but dynamically shifts between the nucleus and the cytoplasm in response to signals (27). To asses a possible role of soloSET, we constructed transgenic lines expressing RNAi-SET. Transgenic plants displayed strong phenotypes: precocious flowering (occurring at a stage with only four true leaves), asymmetric rosettes (note different sizes of leaves 3 and 4), aberrant flowers and chlorosis (Figure 2c). Aberrant flowers and precocious flowering were displayed also by atx1 mutants (5), although never as early as at a four-leaf stage. Also, we have not observed chlorosis under normal watering and long day conditions in atx1 mutants. Despite these perceived differences, however, we concluded that the visible phenotypes, alone, could not be reliable indicates of soloSET function. Consequently, we focused on determining its role at the cellular and molecular levels.Figure 2.


A cytoplasm-specific activity encoded by the Trithorax-like ATX1 gene.

Ndamukong I, Lapko H, Cerny RL, Avramova Z - Nucleic Acids Res. (2011)

Cytoplasmic localization of soloSET and transgenic plants expressing RNAi-SET. (a) Transiently expressed GFP-soloSET fusion protein in tobacco leaf cells is detected only in cytoplasm. Arrows point to perinuclearly localized green signal. (b) Nuclearly localized full-size ATX1-GFP fusion protein is shown for comparison. Chloroplasts are shown in red (chlorophyll autoflorescence). Bars are 20 µm. (c) transgenic Arabidopsis plants expressing RNAi-SET showing precocious flowering (at the stage of only four true leaves), chlorosis in sepals and inflorescences, and a flower with abnormal short stamen (arrowhead) and asymmetric petals (arrows).
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3113559&req=5

Figure 2: Cytoplasmic localization of soloSET and transgenic plants expressing RNAi-SET. (a) Transiently expressed GFP-soloSET fusion protein in tobacco leaf cells is detected only in cytoplasm. Arrows point to perinuclearly localized green signal. (b) Nuclearly localized full-size ATX1-GFP fusion protein is shown for comparison. Chloroplasts are shown in red (chlorophyll autoflorescence). Bars are 20 µm. (c) transgenic Arabidopsis plants expressing RNAi-SET showing precocious flowering (at the stage of only four true leaves), chlorosis in sepals and inflorescences, and a flower with abnormal short stamen (arrowhead) and asymmetric petals (arrows).
Mentions: Transient expression of a soloSET-GFP fusion protein in tobacco leaf cells revealed that it was present only in the cytoplasm (Figure 2a). This is in contrast to ATX1-GFP, which localizes in the nucleus (Figure 2b) but dynamically shifts between the nucleus and the cytoplasm in response to signals (27). To asses a possible role of soloSET, we constructed transgenic lines expressing RNAi-SET. Transgenic plants displayed strong phenotypes: precocious flowering (occurring at a stage with only four true leaves), asymmetric rosettes (note different sizes of leaves 3 and 4), aberrant flowers and chlorosis (Figure 2c). Aberrant flowers and precocious flowering were displayed also by atx1 mutants (5), although never as early as at a four-leaf stage. Also, we have not observed chlorosis under normal watering and long day conditions in atx1 mutants. Despite these perceived differences, however, we concluded that the visible phenotypes, alone, could not be reliable indicates of soloSET function. Consequently, we focused on determining its role at the cellular and molecular levels.Figure 2.

Bottom Line: It is encoded from an internal promoter in the ATX1 locus as an isoform containing only the SET domain (soloSET).It is located exclusively in the cytoplasm and its substrate is the elongation factor 1A (EF1A).Loss of SET, but not of the histone modifying ATX1-SET activity, affects cytoskeletal actin bundling illustrating that the two isoforms have distinct functions in Arabidopsis cells.

View Article: PubMed Central - PubMed

Affiliation: School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, USA.

ABSTRACT
Eukaryotes produce multiple products from a single gene locus by alternative splicing, translation or promoter usage as mechanisms expanding the complexity of their proteome. Trithorax proteins, including the Arabidopsis Trithorax-like protein ATX1, are histone modifiers regulating gene activity. Here, we report that a novel member of the Trithorax family has a role unrelated to chromatin. It is encoded from an internal promoter in the ATX1 locus as an isoform containing only the SET domain (soloSET). It is located exclusively in the cytoplasm and its substrate is the elongation factor 1A (EF1A). Loss of SET, but not of the histone modifying ATX1-SET activity, affects cytoskeletal actin bundling illustrating that the two isoforms have distinct functions in Arabidopsis cells.

Show MeSH
Related in: MedlinePlus