Rpd3S Histone Deacetylase Complex Research Articles

Identification and characterization of FpRco1 in regulating vegetative growth and pathogenicity based on T-DNA insertion in Fusarium pseudograminearum

Fusarium pseudograminearum is a devastating pathogen that causes Fusarium crown rot (FCR) in wheat and poses a significant threat to wheat production in terms of grain yield and quality. However, the mechanism by which F. pseudograminearum infects wheat remains unclear. In this study, we aimed to elucidate these mechanisms by constructing a T-DNA insertion mutant library for the highly virulent strain WZ-8A of F. pseudograminearum. By screening this mutant library, we identified nine independent mutants that displayed impaired pathogenesis in barley leaves. Among these mutants, one possessed a disruption in the gene FpRCO1 that is an ortholog of Saccharomyces cerevisiae RCO1, encoding essential component of the Rpd3S histone deacetylase complex in F. pseudograminearum. To further investigate the role of FpRCO1 in F. pseudograminearum, we employed a split-marker approach to knock out FpRCO1 in F. pseudograminearum WZ-8A. FpRCO1 deletion mutants exhibit reduced vegetative growth, conidium production, and virulence in wheat coleoptiles and barley leaves, whereas the complementary strain restores these phenotypes. Moreover, under stress conditions, the FpRCO1 deletion mutants exhibited increased sensitivity to NaCl, sorbitol, and SDS, but possessed reduced sensitivity to H2O2 compared to these characteristics in the wild-type strain. RNA-seq analysis revealed that deletion of FpRCO1 affected gene expression (particularly the downregulation of TRI gene expression), thus resulting in significantly reduced deoxynivalenol (DON) production. In summary, our findings highlight the pivotal role of FpRCO1 in regulating vegetative growth and development, asexual reproduction, DON production, and pathogenicity of F. pseudograminearum. This study provides valuable insights into the molecular mechanisms underlying F. pseudograminearum infection in wheat and may pave the way for the development of novel strategies to combat this devastating disease.

Structural basis of nucleosome deacetylation and DNA linker tightening by Rpd3S histone deacetylase complex.

In Saccharomyces cerevisiae, cryptic transcription at the coding region is prevented by the activity of Sin3 histone deacetylase (HDAC) complex Rpd3S, which is carried by the transcribing RNA polymerase II (RNAPII) to deacetylate and stabilize chromatin. Despite its fundamental importance, the mechanisms by which Rpd3S deacetylates nucleosomes and regulates chromatin dynamics remain elusive. Here, we determined several cryo-EM structures of Rpd3S in complex with nucleosome core particles (NCPs), including the H3/H4 deacetylation states, the alternative deacetylation state, the linker tightening state, and a state in which Rpd3S co-exists with the Hho1 linker histone on NCP. These structures suggest that Rpd3S utilizes a conserved Sin3 basic surface to navigate through the nucleosomal DNA, guided by its interactions with H3K36 methylation and the extra-nucleosomal DNA linkers, to target acetylated H3K9 and sample other histone tails. Furthermore, our structures illustrate that Rpd3S reconfigures the DNA linkers and acts in concert with Hho1 to engage the NCP, potentially unraveling how Rpd3S and Hho1 work in tandem for gene silencing.

Biochemical Characterization of the TINTIN Module of the NuA4 Complex Reveals Allosteric Regulation of Nucleosome Interaction.

Trimer Independent of NuA4 involved in Transcription Interactions with Nucleosomes (TINTIN) is an integral module of the essential yeast lysine acetyltransferase complex NuA4 that plays key roles in transcription regulation and DNA repair. Composed of Eaf3, Eaf5, and Eaf7, TINTIN mediates targeting of NuA4 to chromatin through the chromodomain-containing subunit Eaf3 that is shared with the Rpd3S histone deacetylase complex. How Eaf3 mediates chromatin interaction in the context of TINTIN and how is it different from what has been observed in Rpd3S is unclear. Here, we reconstituted recombinant TINTIN and its subassemblies and characterized their biochemical and structural properties. Our coimmunoprecipitation, AlphaFold2 modeling, and hydrogen deuterium exchange mass spectrometry (HDX-MS) analyses revealed that the Eaf3 MRG domain contacts Eaf7 and this binding induces conformational changes throughout Eaf3. Nucleosome-binding assays showed that Eaf3 and TINTIN interact non-specifically with the DNA on nucleosomes. Furthermore, integration into TINTIN enhances the affinity of Eaf3 toward nucleosomes and this improvement is a result of allosteric activation of the Eaf3 chromodomain. Negative stain electron microscopy (EM) analysis revealed that TINTIN binds to the edge of nucleosomes with increased specificity in the presence of H3K36me3. Collectively, our work provides insights into the dynamics of TINTIN and the mechanism by which its interactions with chromatin are regulated.

Suppressor mutations that make the essential transcription factor Spn1/Iws1 dispensable in Saccharomyces cerevisiae.

Spn1/Iws1 is an essential eukaryotic transcription elongation factor that is conserved from yeast to humans as an integral member of the RNA polymerase II elongation complex. Several studies have shown that Spn1 functions as a histone chaperone to control transcription, RNA splicing, genome stability, and histone modifications. However, the precise role of Spn1 is not understood, and there is little understanding of why it is essential for viability. To address these issues, we have isolated 8 suppressor mutations that bypass the essential requirement for Spn1 in Saccharomyces cerevisiae. Unexpectedly, the suppressors identify several functionally distinct complexes and activities, including the histone chaperone FACT, the histone methyltransferase Set2, the Rpd3S histone deacetylase complex, the histone acetyltransferase Rtt109, the nucleosome remodeler Chd1, and a member of the SAGA coactivator complex, Sgf73. The identification of these distinct groups suggests that there are multiple ways in which Spn1 bypass can occur, including changes in histone acetylation and alterations in other histone chaperones. Thus, Spn1 may function to overcome repressive chromatin by multiple mechanisms during transcription. Our results suggest that bypassing a subset of these functions allows viability in the absence of Spn1.

Combinatorial Genetic Control of Rpd3S Through Histone H3K4 and H3K36 Methylation in Budding Yeast

Much of euchromatin regulation occurs through reversible methylation of histone H3 lysine-4 and lysine-36 (H3K4me and H3K36me). Using the budding yeast Saccharomyces cerevisiae, we previously found that levels of H3K4me modulated temperature sensitive alleles of the transcriptional elongation complex Spt6-Spn1 through an unknown H3K4me effector pathway. Here we identify the Rpd3S histone deacetylase complex as the H3K4me effector underlying these Spt6-Spn1 genetic interactions. Exploiting these Spt6-Spn1 genetic interactions, we show that H3K4me and H3K36me collaboratively impact Rpd3S function in an opposing manner. H3K36me is deposited by the histone methyltransferase Set2 and is known to promote Rpd3S function at RNA PolII transcribed open reading frames. Using genetic epistasis experiments, we find that mutations perturbing the Set2-H3K36me-Rpd3S pathway suppress the growth defects caused by temperature sensitive alleles of SPT6 and SPN1, illuminating that this pathway antagonizes Spt6-Spn1. Using these sensitive genetic assays, we also identify a role for H3K4me in antagonizing Rpd3S that functions through the Rpd3S subunit Rco1, which is known to bind H3 N-terminal tails in a manner that is prevented by H3K4me. Further genetic experiments reveal that the H3K4 and H3K36 demethylases JHD2 and RPH1 mediate this combinatorial control of Rpd3S. Finally, our studies also show that the Rpd3L complex, which acts at promoter-proximal regions of PolII transcribed genes, counters Rpd3S for genetic modulation of Spt6-Spn1, and that these two Rpd3 complexes balance the activities of each other. Our findings present the first evidence that H3K4me and H3K36me act combinatorially to control Rpd3S.

Combinatorial Histone Readout by the Dual Plant Homeodomain (PHD) Fingers of Rco1 Mediates Rpd3S Chromatin Recruitment and the Maintenance of Transcriptional Fidelity

The plant homeodomain (PHD) finger is found in many chromatin-associated proteins and functions to recruit effector proteins to chromatin through its ability to bind both methylated and unmethylated histone residues. Here, we show that the dual PHD fingers of Rco1, a member of the Rpd3S histone deacetylase complex recruited to transcribing genes, operate in a combinatorial manner in targeting the Rpd3S complex to histone H3 in chromatin. Although mutations in either the first or second PHD finger allow for Rpd3S complex formation, the assembled complexes from these mutants cannot recognize nucleosomes or function to maintain chromatin structure and prevent cryptic transcriptional initiation from within transcribed regions. Taken together, our findings establish a critical role of combinatorial readout in maintaining chromatin organization and in enforcing the transcriptional fidelity of genes.

A novel CRE recombinase assay for quantification of GAL10-non coding RNA suppression on transcriptional leakage

Eukaryotic promoters are tightly regulated and often securely repressed. However, recent reports indicated that transcripts originating from the strictly regulated GAL1-10 promoter can be detected by single-yeast cell imaging under repressive conditions. Such leaky, noisy transcription events were suppressed by a long non-coding RNA (GAL10-ncRNA) transcribed within the GAL1-10 locus. It was further suggested that GAL10-ncRNA repression of GAL1-10 promoter leakage tunes the bimodal expression pattern of the GAL network. Independent evidence has indicated that GAL10-ncRNA transcription establishes a repressive chromatin structure through the Set2 histone methyl-transferase and the Rpd3s histone deacetylase complex. In this report we set up a novel, simple genetic Cre recombinase assay in order to readily quantify transcriptional leakage from tightly repressed promoters. By applying this method we demonstrate that GAL10-ncRNA, Set2p and Rpd3p all suppress leaky GAL1-10 driven transcription. However, GAL10-ncRNA repression is not mediated by Set2p or Rpd3p. Moreover, as opposed to GAL10-ncRNA transcription, Set2 and Rpd3 do not influence the bimodal expression of GAL genes, despite their effect on GAL1-10 promoter leakage. We suggest that GAL10-ncRNA tunes the expression of GAL genes by additional mechanisms besides suppressing leaky transcription from the GAL1-10 promoter.

Homodimeric PHD Domain-containing Rco1 Subunit Constitutes a Critical Interaction Hub within the Rpd3S Histone Deacetylase Complex

Recognition of histone post-translational modifications is pivotal for directing chromatin-modifying enzymes to specific genomic regions and regulating their activities. Emerging evidence suggests that other structural features of nucleosomes also contribute to precise targeting of downstream chromatin complexes, such as linker DNA, the histone globular domain, and nucleosome spacing. However, how chromatin complexes coordinate individual interactions to achieve high affinity and specificity remains unclear. The Rpd3S histone deacetylase utilizes the chromodomain-containing Eaf3 subunit and the PHD domain-containing Rco1 subunit to recognize nucleosomes that are methylated at lysine 36 of histone H3 (H3K36me). We showed previously that the binding of Eaf3 to H3K36me can be allosterically activated by Rco1. To investigate how this chromatin recognition module is regulated in the context of the Rpd3S complex, we first determined the subunit interaction network of Rpd3S. Interestingly, we found that Rpd3S contains two copies of the essential subunit Rco1, and both copies of Rco1 are required for full functionality of Rpd3S. Our functional dissection of Rco1 revealed that besides its known chromatin-recognition interfaces, other regions of Rco1 are also critical for Rpd3S to recognize its nucleosomal substrates and functionin vivo. This unexpected result uncovered an important and understudied aspect of chromatin recognition. It suggests that precisely reading modified chromatin may not only need the combined actions of reader domains but also require an internal signaling circuit that coordinates the individual actions in a productive way.

Histone H3K36 trimethylation is essential for multiple silencing mechanisms in fission yeast.

In budding yeast, Set2 catalyzes di- and trimethylation of H3K36 (H3K36me2 and H3K36me3) via an interaction between its Set2–Rpb1 interaction (SRI) domain and C-terminal repeats of RNA polymerase II (Pol2) phosphorylated at Ser2 and Ser5 (CTD-S2,5-P). H3K36me2 is sufficient for recruitment of the Rpd3S histone deacetylase complex to repress cryptic transcription from transcribed regions. In fission yeast, Set2 is also responsible for H3K36 methylation, which represses a subset of RNAs including heterochromatic and subtelomeric RNAs, at least in part via recruitment of Clr6 complex II, a homolog of Rpd3S. Here, we show that CTD-S2P-dependent interaction of fission yeast Set2 with Pol2 via the SRI domain is required for formation of H3K36me3, but not H3K36me2. H3K36me3 silenced heterochromatic and subtelomeric transcripts mainly through post-transcriptional and transcriptional mechanisms, respectively, whereas H3K36me2 was not enough for silencing. Clr6 complex II appeared not to be responsible for heterochromatic silencing by H3K36me3. Our results demonstrate that H3K36 methylation has multiple outputs in fission yeast; these findings provide insights into the distinct roles of H3K36 methylation in metazoans, which have different enzymes for synthesis of H3K36me1/2 and H3K36me3.

Nucleosome Contact Triggers Conformational Changes of Rpd3S Driving High-Affinity H3K36me Nucleosome Engagement

The Rpd3S histone deacetylase complex utilizes two subunits, Eaf3 and Rco1, to recognize nucleosomes methylated at H3K36 (H3K36me) with high affinity and strong specificity. However, the chromobarrel domain of Eaf3 (CHD) that is responsible for H3K36me recognition only binds weakly and with little specificity to histone peptides. Here, using deuterium exchange mass spectrometry (DXMS), we detected conformational changes of Rpd3S upon its contact with chromatin. Interestingly, we found that the Sin3-interacting domain of Rco1 (SID) allosterically stimulates preferential binding of Eaf3 to H3K36-methylated peptides. This activation is tightly regulated by an autoinhibitory mechanism to ensure optimal multivalent engagement of Rpd3S with nucleosomes. Lastly, we identified mutations at the interface between SID and Eaf3 that do not disrupt complex integrity but severely compromise Rpd3S functions in vitro and in vivo, suggesting that the nucleosome-induced conformational changes are essential for chromatin recognition.

Chromatin Remodelers Fine-Tune H3K36me-Directed Deacetylation of Neighbor Nucleosomes by Rpd3S

Chromatin remodelers have been implicated in the regulation of histone-modifying complexes. However, the underlying mechanism remains poorly understood. The Rpd3S histone deacetylase complex is recruited by elongating RNA polymerase II to remove histone acetylation at coding regions in a manner that is dependent on methylation of lysine 36 on histone 3 (H3K36me), and Rpd3S prefers dinucleosomes. Here, we show that the binding of Rpd3S to dinucleosomes and its catalytic activity are sensitive to the length of nucleosomal linker in a nonlinear fashion. Intriguingly, we found that H3K36me on one nucleosome stimulates Rpd3S to deacetylate the neighboring nucleosomes when those two nucleosomes are within an optimal distance. Finally, we demonstrate that chromatin remodelers enhance Rpd3S activity by altering nucleosomal spacing, suggesting that chromatin remodelers prime chromatin configuration to fine-tune subsequent histone modification reactions. This mechanism is important for accurate temporal control of chromatin dynamics during the transcription elongation cycle.

Set2 methylation of histone H3 lysine 36 suppresses histone exchange on transcribed genes

Set2-mediated methylation of histone H3 at Lys 36 (H3K36me) is a co-transcriptional event that is necessary for the activation of the Rpd3S histone deacetylase complex, thereby maintaining the coding region of genes in a hypoacetylated state. In the absence of Set2, H3K36 or Rpd3S acetylated histones accumulate on open reading frames (ORFs), leading to transcription initiation from cryptic promoters within ORFs. Although the co-transcriptional deacetylation pathway is well characterized, the factors responsible for acetylation are as yet unknown. Here we show that, in yeast, co-transcriptional acetylation is achieved in part by histone exchange over ORFs. In addition to its function of targeting and activating the Rpd3S complex, H3K36 methylation suppresses the interaction of H3 with histone chaperones, histone exchange over coding regions and the incorporation of new acetylated histones. Thus, Set2 functions both to suppress the incorporation of acetylated histones and to signal for the deacetylation of these histones in transcribed genes. By suppressing spurious cryptic transcripts from initiating within ORFs, this pathway is essential to maintain the accuracy of transcription by RNA polymerase II.

Multivalent di-nucleosome recognition enables the Rpd3S histone deacetylase complex to tolerate decreased H3K36 methylation levels

The Rpd3S histone deacetylase complex represses cryptic transcription initiation within coding regions by maintaining the hypo-acetylated state of transcribed chromatin. Rpd3S recognizes methylation of histone H3 at lysine 36 (H3K36me), which is required for its deacetylation activity. Rpd3S is able to function over a wide range of H3K36me levels, making this a unique system to examine how chromatin regulators tolerate the reduction of their recognition signal. Here, we demonstrated that Rpd3S makes histone modification-independent contacts with nucleosomes, and that Rpd3S prefers di-nucleosome templates since two binding surfaces can be readily accessed simultaneously. Importantly, this multivalent mode of interaction across two linked nucleosomes allows Rpd3S to tolerate a two-fold intramolecular reduction of H3K36me. Our data suggest that chromatin regulators utilize an intrinsic di-nucleosome-recognition mechanism to prevent compromised function when their primary recognition modifications are diluted.

Features of Cryptic Promoters and Their Varied Reliance on Bromodomain-Containing Factors

The Set2-Rpd3S pathway is important for the control of transcription memory. Mutation of components of this pathway results in cryptic transcription initiation within the coding region of approximately 30% of yeast genes. Specifically, deletion of the Set2 histone methyltransferase or Rco1, a component of the Rpd3S histone deacetylase complex leads to hyperacetylation of certain open reading frames (ORFs). We used this mutant as a system to study the role of histone modifications and co-activator recruitment in preinitiation complex (PIC) formation. Specifically, we looked at the dependence of promoters on the bromodomain-containing RSC complex and the Bdf1 protein. We found that the dependence of cryptic promoters for these proteins varied. Overall, our data indicate that cryptic promoters are independently regulated, and their activation is dependent on factors that govern gene activation at canonical promoters.

A Nucleosome Surface Formed by Histone H4, H2A, and H3 Residues Is Needed for Proper Histone H3 Lys36 Methylation, Histone Acetylation, and Repression of Cryptic Transcription

Set2-mediated H3 Lys(36) methylation is a histone modification that has been demonstrated to function in transcriptional elongation by recruiting the Rpd3S histone deacetylase complex to repress intragenic cryptic transcription. Recently, we identified a trans-histone pathway in which the interaction between the N terminus of Set2 and histone H4 Lys(44) is needed to mediate trans-histone H3 Lys(36) di- and trimethylation. In the current study, we demonstrate that mutation of the lysine 44 residue in histone H4 or the Set2 mutant lacking the histone H4 interaction motif leads to intragenic cryptic transcripts, indicating that the Set2 and histone H4 interaction is important to repress intragenic cryptic transcription. We also determine that histone H2A residues (Leu(116) and Leu(117)), which are in close proximity to histone H4 Lys(44), are needed for proper trans-histone H3 Lys(36) methylation. Similar to H4 Lys(44) mutants, histone H2A Leu(116) and Leu(117) mutations exhibited decreased H3 Lys(36) di- and trimethylation, increased histone H4 acetylation, increased resistance to 6-azauracil, and cryptic transcription. Interestingly, the combined histone H4 Lys(44) and H2A mutations have more severe methylation defects and increased H4 acetylation levels. Furthermore, we identify that additional histone H2A and H3 core residues are also needed for H3 Lys(36) di- and trimethylation. Overall, our results show and suggest that multiple H4, H2A, and H3 residues contribute to and form a Set2 docking/recognition site on the nucleosomal surface so that proper Set2-mediated H3 Lys(36) di- and trimethylation, histone acetylation, and transcriptional elongation can occur.

NcRNA transcription makes its mark

ncRNA transcription makes its mark

Histone H3 Lysine 36 Dimethylation (H3K36me2) Is Sufficient to Recruit the Rpd3s Histone Deacetylase Complex and to Repress Spurious Transcription

Histone methylation is associated with both transcription activation and repression. However, the functions of different states of methylation remain largely elusive. Here, using methyl-lysine analog technology, we demonstrate that the histone deacetylase complex, Rpd3S, can distinguish the nucleosomes methylated to different extents and that K36me2 is sufficient to target Rpd3S in vitro. Through a genome-wide survey, we identified a few mutants in which the level of K36me3 is significantly reduced, whereas the level of K36me2 is sustained. Transcription analysis and genome-wide histone modification studies on these mutants suggested that K36me2 is sufficient to target Rpd3S in vivo, thereby maintaining a functional Set2-Rpd3S pathway.

Noncoding transcription controls downstream promoters to regulate T-cell receptor α recombination

The T early alpha (TEA) promoter in the murine Tcra locus generates noncoding transcripts that extend across the 65 kb Jalpha array. Here, we have analyzed the significance of TEA transcription for Tcra locus regulation through the targeted introduction of a transcription terminator downstream of the TEA promoter. We demonstrate that noncoding transcription driven by this single promoter can instruct both positively and negatively the activity of downstream Jalpha promoters, and can similarly instruct alterations in Jalpha chromatin structure and Jalpha recombination. TEA transcription activates promoters associated with relatively proximal Jalpha segments and stimulates histone acetylation, histone methylation and chromatin accessibility in this region. In contrast, at more distal locations, TEA transcription inhibits promoter activity through transcriptional interference and suppresses chromatin accessibility. In combination, these effects target initial Valpha-to-Jalpha recombination to TEA-proximal Jalpha segments and promote the ordered usage of the Jalpha array. The ability of TEA transcription to coordinate the activity of multiple downstream promoters maximizes the biological potential of the Jalpha array and diversifies the Tcra repertoire.

Combined Action of PHD and Chromo Domains Directs the Rpd3S HDAC to Transcribed Chromatin

Nucleosomes must be deacetylated behind elongating RNA polymerase II to prevent cryptic initiation of transcription within the coding region. RNA polymerase II signals for deacetylation through the methylation of histone H3 lysine 36 (H3K36), which provides the recruitment signal for the Rpd3S histone deacetylase complex (HDAC). The recognition of methyl H3K36 by Rpd3S requires the chromodomain of its Eaf3 subunit. Paradoxically, Eaf3 is also a subunit of the NuA4 acetyltransferase complex, yet NuA4 does not recognize methyl H3K36 nucleosomes. In Saccharomyces cerevisiae, we found that methyl H3K36 nucleosome recognition by Rpd3S also requires the plant homeobox domain (PHD) of its Rco1 subunit. Thus, the coupled chromo and PHD domains of Rpd3S specify recognition of the methyl H3K36 mark, demonstrating the first combinatorial domain requirement within a protein complex to read a specific histone code.

Histone H3 Lysine 36 Methylation Antagonizes Silencing in Saccharomyces cerevisiae Independently of the Rpd3S Histone Deacetylase Complex

In yeast, methylation of histone H3 on lysine 36 (H3-K36) is catalyzed by the NSD1 leukemia oncoprotein homolog Set2. The histone deacetylase complex Rpd3S is recruited to chromatin via binding of the chromodomain protein Eaf3 to methylated H3-K36 to prevent erroneous transcription initiation. Here we identify a distinct function for H3-K36 methylation. We used random mutagenesis of histones H3 and H4 followed by a reporter-based screen to identify residues necessary to prevent the ectopic spread of silencing from the silent mating-type locus HMRa into flanking euchromatin. Mutations in H3-K36 or deletion of SET2 caused ectopic silencing of a heterochromatin-adjacent reporter. Transcriptional profiling revealed that telomere-proximal genes are enriched for those that display decreased expression in a set2Delta strain. Deletion of SIR4 rescued the expression defect of 26 of 37 telomere-proximal genes with reduced expression in set2Delta cells, implying that H3-K36 methylation prevents the spread of telomeric silencing. Indeed, Sir3 spreads from heterochromatin into neighboring euchromatin in set2Delta cells. Furthermore, genetic experiments demonstrated that cells lacking the Rpd3S-specific subunits Eaf3 or Rco1 did not display the anti-silencing phenotype of mutations in SET2 or H3-K36. Thus, antagonism of silencing is independent of the only known effector of this conserved histone modification.