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Overexpression of AtBMI1C, a polycomb group protein gene, accelerates flowering in Arabidopsis.

Li W, Wang Z, Li J, Yang H, Cui S, Wang X, Ma L - PLoS ONE (2011)

Bottom Line: No change in the H3K27me3 level in FLC chromatin was detected in an AtBMI1C-overexpressing line.Our results suggest that AtBMI1C participates in flowering time control by regulating the expression of FLC; moreover, the repression of FLC by AtBMI1C is not due to the activity of PRC2.Instead, it is likely the result of PRC1 activity, into which AtBMI1C is integrated.

View Article: PubMed Central - PubMed

Affiliation: Hebei Key Laboratory of Molecular Cell Biology, College of Biological Sciences, Hebei Normal University, Shijiazhuang, Hebei, China.

ABSTRACT
Polycomb group protein (PcG)-mediated gene silencing is emerging as an essential developmental regulatory mechanism in eukaryotic organisms. PcGs inactivate or maintain the silenced state of their target chromatin by forming complexes, including Polycomb Repressive Complex 1 (PRC1) and 2 (PRC2). Three PRC2 complexes have been identified and characterized in Arabidopsis; of these, the EMF and VRN complexes suppress flowering by catalyzing the trimethylation of lysine 27 on histone H3 of FLOWER LOCUS T (FT) and FLOWER LOCUS C (FLC). However, little is known about the role of PRC1 in regulating the floral transition, although AtRING1A, AtRING1B, AtBMI1A, and AtBMI1B are believed to regulate shoot apical meristem and embryonic development as components of PRC1. Moreover, among the five RING finger PcGs in the Arabidopsis genome, four have been characterized. Here, we report that the fifth, AtBMI1C, is a novel, ubiquitously expressed nuclear PcG protein and part of PRC1, which is evolutionarily conserved with Psc and BMI1. Overexpression of AtBMI1C caused increased H2A monoubiquitination and flowering defects in Arabidopsis. Both the suppression of FLC and activation of FT were observed in AtBMI1C-overexpressing lines, resulting in early flowering. No change in the H3K27me3 level in FLC chromatin was detected in an AtBMI1C-overexpressing line. Our results suggest that AtBMI1C participates in flowering time control by regulating the expression of FLC; moreover, the repression of FLC by AtBMI1C is not due to the activity of PRC2. Instead, it is likely the result of PRC1 activity, into which AtBMI1C is integrated.

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Expression of FLC and FT in AtBMI1C-overexpressing lines.(A) Expression of FLC in AtBMI1C-overexpressing lines harboring p35S::ATBMI1C-YFP as determined by quantitative real-time RT-PCR. (B) FT expression in AtBMI1C-overexpressing lines harboring p35S::AtBMI1C-YFP as determined by quantitative real-time RT-PCR. (C) FLC expression in transgenic lines harboring pAP1::AtBMI1C-GFP as determined by quantitative real-time RT-PCR. (D) FT expression in transgenic lines harboring pAP1::AtBMI1C-GFP as determined by quantitative RT-PCR. Total RNA was isolated from ten-day-old transgenic or wild-type seedlings. FLC or FT expression was measured by quantitative real-time RT-PCR using ACTIN2/7 as an endogenous control. The values are the mean ± SD of three independent experiments.
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pone-0021364-g007: Expression of FLC and FT in AtBMI1C-overexpressing lines.(A) Expression of FLC in AtBMI1C-overexpressing lines harboring p35S::ATBMI1C-YFP as determined by quantitative real-time RT-PCR. (B) FT expression in AtBMI1C-overexpressing lines harboring p35S::AtBMI1C-YFP as determined by quantitative real-time RT-PCR. (C) FLC expression in transgenic lines harboring pAP1::AtBMI1C-GFP as determined by quantitative real-time RT-PCR. (D) FT expression in transgenic lines harboring pAP1::AtBMI1C-GFP as determined by quantitative RT-PCR. Total RNA was isolated from ten-day-old transgenic or wild-type seedlings. FLC or FT expression was measured by quantitative real-time RT-PCR using ACTIN2/7 as an endogenous control. The values are the mean ± SD of three independent experiments.

Mentions: To explore the molecular mechanisms responsible for the change in flowering time in our AtBMI1C-overexpressing lines, FLC and FT expression was examined by quantitative RT-PCR. The expression of FLC in lines 35S-14 and 35S-27 was 2.5 times lower than that in wild type (Figure 7A). As a result of the down-regulation of FLC, the expression of FT in lines 35S-14 and 35S-27 was about five times higher than that in wild type (Figure 7B). Similarly, the repression of FLC in lines A-9, A-13, and A-14 was also observed (Figure 7C). An increase in FT expression of 3-4.5 times in lines A-9, A-13, and A-14 was detected (Figure 7D). These results suggest that AtBMI1C overexpression promotes flowering by repressing FLC expression and activating FT expression.


Overexpression of AtBMI1C, a polycomb group protein gene, accelerates flowering in Arabidopsis.

Li W, Wang Z, Li J, Yang H, Cui S, Wang X, Ma L - PLoS ONE (2011)

Expression of FLC and FT in AtBMI1C-overexpressing lines.(A) Expression of FLC in AtBMI1C-overexpressing lines harboring p35S::ATBMI1C-YFP as determined by quantitative real-time RT-PCR. (B) FT expression in AtBMI1C-overexpressing lines harboring p35S::AtBMI1C-YFP as determined by quantitative real-time RT-PCR. (C) FLC expression in transgenic lines harboring pAP1::AtBMI1C-GFP as determined by quantitative real-time RT-PCR. (D) FT expression in transgenic lines harboring pAP1::AtBMI1C-GFP as determined by quantitative RT-PCR. Total RNA was isolated from ten-day-old transgenic or wild-type seedlings. FLC or FT expression was measured by quantitative real-time RT-PCR using ACTIN2/7 as an endogenous control. The values are the mean ± SD of three independent experiments.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3119047&req=5

pone-0021364-g007: Expression of FLC and FT in AtBMI1C-overexpressing lines.(A) Expression of FLC in AtBMI1C-overexpressing lines harboring p35S::ATBMI1C-YFP as determined by quantitative real-time RT-PCR. (B) FT expression in AtBMI1C-overexpressing lines harboring p35S::AtBMI1C-YFP as determined by quantitative real-time RT-PCR. (C) FLC expression in transgenic lines harboring pAP1::AtBMI1C-GFP as determined by quantitative real-time RT-PCR. (D) FT expression in transgenic lines harboring pAP1::AtBMI1C-GFP as determined by quantitative RT-PCR. Total RNA was isolated from ten-day-old transgenic or wild-type seedlings. FLC or FT expression was measured by quantitative real-time RT-PCR using ACTIN2/7 as an endogenous control. The values are the mean ± SD of three independent experiments.
Mentions: To explore the molecular mechanisms responsible for the change in flowering time in our AtBMI1C-overexpressing lines, FLC and FT expression was examined by quantitative RT-PCR. The expression of FLC in lines 35S-14 and 35S-27 was 2.5 times lower than that in wild type (Figure 7A). As a result of the down-regulation of FLC, the expression of FT in lines 35S-14 and 35S-27 was about five times higher than that in wild type (Figure 7B). Similarly, the repression of FLC in lines A-9, A-13, and A-14 was also observed (Figure 7C). An increase in FT expression of 3-4.5 times in lines A-9, A-13, and A-14 was detected (Figure 7D). These results suggest that AtBMI1C overexpression promotes flowering by repressing FLC expression and activating FT expression.

Bottom Line: No change in the H3K27me3 level in FLC chromatin was detected in an AtBMI1C-overexpressing line.Our results suggest that AtBMI1C participates in flowering time control by regulating the expression of FLC; moreover, the repression of FLC by AtBMI1C is not due to the activity of PRC2.Instead, it is likely the result of PRC1 activity, into which AtBMI1C is integrated.

View Article: PubMed Central - PubMed

Affiliation: Hebei Key Laboratory of Molecular Cell Biology, College of Biological Sciences, Hebei Normal University, Shijiazhuang, Hebei, China.

ABSTRACT
Polycomb group protein (PcG)-mediated gene silencing is emerging as an essential developmental regulatory mechanism in eukaryotic organisms. PcGs inactivate or maintain the silenced state of their target chromatin by forming complexes, including Polycomb Repressive Complex 1 (PRC1) and 2 (PRC2). Three PRC2 complexes have been identified and characterized in Arabidopsis; of these, the EMF and VRN complexes suppress flowering by catalyzing the trimethylation of lysine 27 on histone H3 of FLOWER LOCUS T (FT) and FLOWER LOCUS C (FLC). However, little is known about the role of PRC1 in regulating the floral transition, although AtRING1A, AtRING1B, AtBMI1A, and AtBMI1B are believed to regulate shoot apical meristem and embryonic development as components of PRC1. Moreover, among the five RING finger PcGs in the Arabidopsis genome, four have been characterized. Here, we report that the fifth, AtBMI1C, is a novel, ubiquitously expressed nuclear PcG protein and part of PRC1, which is evolutionarily conserved with Psc and BMI1. Overexpression of AtBMI1C caused increased H2A monoubiquitination and flowering defects in Arabidopsis. Both the suppression of FLC and activation of FT were observed in AtBMI1C-overexpressing lines, resulting in early flowering. No change in the H3K27me3 level in FLC chromatin was detected in an AtBMI1C-overexpressing line. Our results suggest that AtBMI1C participates in flowering time control by regulating the expression of FLC; moreover, the repression of FLC by AtBMI1C is not due to the activity of PRC2. Instead, it is likely the result of PRC1 activity, into which AtBMI1C is integrated.

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Related in: MedlinePlus