Methyl recycling activities are co-ordinately regulated during plant development

Pereira, Luiz Alfredo Rodrigues; Todorova, Margarita; Cai, Xing; Makaroff, Christopher A.; Emery, R. J. Neil; Moffatt, Barbara A.

doi:10.1093/jxb/erl275

Cited by 40 publications

(33 citation statements)

References 54 publications

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“…The induction of AtSAHH1, AtADK1 and cytosine DNA methyltransferase genes by cytokinin is consistent with a recent report that methyl recycling activities are coordinately regulated (Pereira et al 2007). Cytosine DNA methyltransferases (MTase) transfer the methyl group from SAM to double-strand DNA.…”

Section: Discussionsupporting

confidence: 91%

Down-regulation of S-adenosyl-l-homocysteine hydrolase reveals a role of cytokinin in promoting transmethylation reactions

Jiang

et al. 2008

Planta

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S-adenosyl-L: -homocysteine hydrolase (SAHH) is a key enzyme for maintenance of cellular transmethylation potential. Although a cytokinin-binding activity had been hypothesized for SAHH, the relation between cytokinin and transmethylation reactions has not been elucidated. Here we show that, of the two Arabidopsis thaliana SAHH genes, AtSAHH1 has a much higher expression level than AtSAHH2. A T-DNA insertion mutant of AtSAHH1 (sahh1-1) and the RNA interference (RNAi) plants (dsAtSAHH2) accumulated a higher level of cytokinins, exhibited phenotypic changes similar to those of cytokinin-overproducers, and their global DNA methylation status was reduced. On the other hand, cytokinins positively regulate the transmethylation pathway genes, including AtSAHH1, AtADK1 (for adenosine kinase), and this regulation involves the cytokinin activity. Furthermore, expression of three cytosine DNA methyltransferase genes examined was inducible by cytokinin treatment. Unlike adenine and adenosine which are SAHH inhibitors, the adenine-type cytokinins have no effect on SAHH activity at protein level. Changing of endogenous cytokinin levels by transgene expression resulted in alterations of DNA methylation status in the sahh1-1 background, suggesting that cytokinins promote DNA methylation, at least under transmethylation stringent conditions. These data demonstrate that the phytohormone cytokinin plays a role in promoting transmethylation reactions, including DNA methylation.

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Section: Discussionsupporting

confidence: 91%

Down-regulation of S-adenosyl-l-homocysteine hydrolase reveals a role of cytokinin in promoting transmethylation reactions

Jiang

et al. 2008

Planta

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“…SAHH reversibly hydrolyzes SAH to homocysteine and adenosine, and removal of adenosine is necessary to shift the equilibrium in favor of hydrolysis (40,41). In plant species including Arabidopsis thaliana, Spinacia oleracea, and Beta vulgaris, ADK is primarily responsible for adenosine salvage and methyl cycle maintenance at all stages of development and also in inflorescence tissues (21,(42)(43)(44). This is consistent with earlier work which showed that L2 expression and ADK inhibition cause TGS reversal in both vegetative and reproductive Arabidopsis plants (24).…”

Section: Discussionsupporting

confidence: 87%

Analysis of Geminivirus AL2 and L2 Proteins Reveals a Novel AL2 Silencing Suppressor Activity

Jackel

Buchmann

Singhal

et al. 2015

J Virol

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Both posttranscriptional and transcriptional gene silencing (PTGS and TGS, respectively) participate in defense against the DNA-containing geminiviruses. As a countermeasure, members of the genus Begomovirus (e.g., Cabbage leaf curl virus) encode an AL2 protein that is both a transcriptional activator and a silencing suppressor. The related L2 protein of Beet curly top virus (genus Curtovirus) lacks transcription activation activity. Previous studies showed that both AL2 and L2 suppress silencing by a mechanism that correlates with adenosine kinase (ADK) inhibition, while AL2 in addition activates transcription of cellular genes that negatively regulate silencing pathways. The goal of this study was to clarify the general means by which these viral proteins inhibit various aspects of silencing. We confirmed that AL2 inhibits systemic silencing spread by a mechanism that requires transcription activation activity. Surprisingly, we also found that reversal of PTGS and TGS by ADK inactivation depended on whether experiments were conducted in vegetative or reproductive Nicotiana benthamiana plants (i.e., before or after the vegetative-to-reproductive transition). While AL2 was able to reverse silencing in both vegetative and reproductive plants, L2 and ADK inhibition were effective only in vegetative plants. This suggests that silencing maintenance mechanisms can change during development or in response to stress. Remarkably, we also observed that AL2 lacking its transcription activation domain could reverse TGS in reproductive plants, revealing a third, previously unsuspected AL2 suppression mechanism that depends on neither ADK inactivation nor transcription activation. IMPORTANCERNA silencing in plants is a multivalent antiviral defense, and viruses respond by elaborating multiple and sometimes multifunctional proteins that inhibit various aspects of silencing. The studies described here add an additional layer of complexity to this interplay. By examining geminivirus AL2 and L2 suppressor activities, we show that L2 is unable to suppress silencing in Nicotiana benthamiana plants that have undergone the vegetative-to-reproductive transition. As L2 was previously shown to be effective in mature Arabidopsis plants, these results illustrate that silencing mechanisms can change during development or in response to stress in ways that may be species specific. The AL2 and L2 proteins are known to share a suppression mechanism that correlates with the ability of both proteins to inhibit ADK, while AL2 in addition can inhibit silencing by transcriptionally activating cellular genes. Here, we also provide evidence for a third AL2 suppression mechanism that depends on neither transcription activation nor ADK inactivation. In addition to revealing the remarkable versatility of AL2, this work highlights the utility of viral suppressors as probes for the analysis of silencing pathways. V iruses belonging to the Geminiviridae package small, circular single-stranded DNA (ssDNA) genomes in unique double icosahedral parti...

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“…S8). In vivo, plants use SAH hydrolase (EC 3.3.1.1) and adenosine kinase (EC 2.7.1.20) to metabolize SAH, thus circumventing its inhibitory effects and promoting SAM regeneration and methyltransferase activities (35).…”

Section: Resultsmentioning

confidence: 99%

4- O -methylation of glucuronic acid in Arabidopsis glucuronoxylan is catalyzed by a domain of unknown function family 579 protein

Urbanowicz

Peña

Ratnaparkhe

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

154

144

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The hemicellulose 4-O-methyl glucuronoxylan is one of the principle components present in the secondary cell walls of eudicotyledonous plants. However, the biochemical mechanisms leading to the formation of this polysaccharide and the effects of modulating its structure on the physical properties of the cell wall are poorly understood. We have identified and functionally characterized an Arabidopsis glucuronoxylan methyltransferase (GXMT) that catalyzes 4-O-methylation of the glucuronic acid substituents of this polysaccharide. AtGXMT1, which was previously classified as a domain of unknown function (DUF) 579 protein, specifically transfers the methyl group from S-adenosyl-L-methionine to O-4 of α-D-glucopyranosyluronic acid residues that are linked to O-2 of the xylan backbone. Biochemical characterization of the recombinant enzyme indicates that GXMT1 is localized in the Golgi apparatus and requires Co 2+ for optimal activity in vitro. Plants lacking GXMT1 synthesize glucuronoxylan in which the degree of 4-O-methylation is reduced by 75%. This result is correlated to a change in lignin monomer composition and an increase in glucuronoxylan release during hydrothermal treatment of secondary cell walls. We propose that the DUF579 proteins constitute a previously undescribed family of cation-dependent, polysaccharide-specific O-methyl-transferases. This knowledge provides new opportunities to selectively manipulate polysaccharide O-methylation and extends the portfolio of structural targets that can be modified either alone or in combination to modulate biopolymer interactions in the plant cell wall.recalcitrance | biosynthesis

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Methyl recycling activities are co-ordinately regulated during plant development

Cited by 40 publications

References 54 publications

Down-regulation of S-adenosyl-l-homocysteine hydrolase reveals a role of cytokinin in promoting transmethylation reactions

Down-regulation of S-adenosyl-l-homocysteine hydrolase reveals a role of cytokinin in promoting transmethylation reactions

Analysis of Geminivirus AL2 and L2 Proteins Reveals a Novel AL2 Silencing Suppressor Activity

4- O -methylation of glucuronic acid in Arabidopsis glucuronoxylan is catalyzed by a domain of unknown function family 579 protein

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