Polycomb Group Proteins RING1A and RING1B Regulate the Vegetative Phase Transition in Arabidopsis

Abstract

Polycomb group (PcG) protein-mediated gene silencing is a major regulatory mechanism in higher eukaryotes that affects gene expression at the transcriptional level. Here, we report that two conserved homologous PcG proteins, RING1A and RING1B (RING1A/B), are required for global H2A monoubiquitination (H2Aub) in Arabidopsis. The mutation of RING1A/B increased the expression of members of the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) gene family and caused an early vegetative phase transition. The early vegetative phase transition observed in ring1a ring1b double mutant plants was dependent on an SPL family gene, and the H2Aub status of the chromatin at SPL locus was dependent on RING1A/B. Moreover, mutation in RING1A/B affected the miRNA156a-mediated vegetative phase transition, and RING1A/B and the AGO7-miR390-TAS3 pathway were found to additively regulate this transition in Arabidopsis. Together, our results demonstrate that RING1A/B regulates the vegetative phase transition in Arabidopsis through the repression of SPL family genes.

The Arabidopsis Nodulin Homeobox Factor AtNDX Interacts with AtRING1A/B and Negatively Regulates Abscisic Acid Signaling

“…Because the atring1a atring1b double mutant is sterile, we were unable to test the seed cotyledon greening phenotype on ABAcontaining medium. We then used a weak double mutant, ring1a-2 ring1b-3, in which a T-DNA fragment is inserted in the promoter region of AtRING1A, resulting in reduced expression of AtRING1A compared with the wild type and a more uniform phenotype (Supplemental Figure 6; Li et al, 2017). The atring1a-2 atring1b-3 double mutant was significantly more sensitive to ABA with respect to inhibition of seedling establishment than the wild type, and ear1-1 served as the ABA-hypersensitive control (Figures 4D to 4G).…”

“…As core components of PRC1, AtRING1A/B mediate H2Aub in vitro and in vivo (Bratzel et al, 2010;Li et al, 2017). As AtNDX interacts with AtRING1A/B, we wanted to know whether the H2Aub level would be affected by AtNDX.…”

“…F17T8/TL841 bulb; PHILIPS) with a light intensity of 60 mE m 22 s 21 under 22-h light/2-h dark at 22°C. The mutants used in this study: Atring1a, Atring1b-2 (Shen et al, 2014), Atring1a 2/2 Atring1b 1/2 (Xu and Shen, 2008), ring1a-2 ring1b-3 (Li et al, 2017), eoc1-4 renamed as ndx-4 in this study (Sun et al, 2013), abi1-1 (Kong et al, 2015), snrk2.2/2.3 (Wang et al, 2018, and abi4-1 (Liu et al, 2010) were in the Columbia (Col-0) background; abi2-1, abi3-1 (Wang et al, 2011) were in the Landsberg erecta (Ler) background; and abi5 were in the Wassilewskija (Ws) background. The transgenic plants AtNDX-FLAG (in eoc1-4, ndx-4 in this study) and AtNDX-eGFP (in eoc1-1, ndx-1) renamed as proAtND-X:AtNDX-Flag and proAtNDX:AtNDX-GFP were as described by Sun et al (2013).…”

Chromatin-Based Regulation of Plant Root Development

“…In Arabidopsis, the histone repressive mark H2Aub1 is catalyzed by the PRC1 RING-finger proteins AtRING1a/b and AtBMI1a/b/c (Bratzel et al, 2010 ; Li et al, 2017 ), which function throughout the life cycle and are implicated in regulating seed germination, vegetative maintenance, flowering time control, floral organ identity, and fertility [(Xu et al, 2005 ; Bratzel et al, 2010 ; Chen et al, 2010 ; Yang et al, 2013 ; Chen D. et al, 2016 )]. PRC1 RING-finger proteins inhibit embryonic traits in primary root mainly through repressing the ectopic expression of seed maturation genes ABSCISIC ACID INSENSITIVE3 ( ABI3 ), FUSCA3 ( FUS3 ), LEAFY COTYLEDON2 ( LEC2 ), and LEAFY COTYLEDON1 ( LEC1 ) (Bratzel et al, 2010 ; Chen et al, 2010 ).…”

The Times They Are A-Changin’: Heterochrony in Plant Development and Evolution

“…Both MIR156 and SPL gene families are directly regulated by epigenetic marks: MIR156 is activated by H3K4me3 and H3K4ac, which are promoted by the SWR1-C complex and the chromatin remodeler BRAHMA, and is repressed by H3K27me3, which is promoted by the Polycomb proteins SWINGER and CURLY LEAF and by the chromatin remodeler PICKLE ( Xu M. et al, 2016 ; Xu Y. et al, 2016 ; Xu M. et al, 2018 ). SPL genes are activated by histone acetylation mediated by the SAGA-like complex and repressed by H2AUb mediated by the Polycomb proteins RING1A and RING1B ( Kim et al, 2015 ; Li et al, 2017 ). The study of plants with loss- or gain-of function of SPL genes has also defined an endogenous flowering pathway in which some SPL genes promote the expression of miR172, which in turn promotes flowering by repressing the APETALA2 family flowering repressors ( Wang et al, 2009 ; Wu et al, 2009 ; Huijser and Schmid, 2011 ).…”