Floral stem cells produce a defined number of floral organs before ceasing to be maintained as stem cells. Therefore, floral stem cells offer an ideal model to study the temporal control of stem cell maintenance within a developmental context. AGAMOUS (AG), a MADS domain transcription factor essential for the termination of floral stem cell fate, has long been thought to repress the stem cell maintenance gene WUSCHEL (WUS) indirectly. Here, we uncover a role of Polycomb Group (PcG) genes in the temporally precise repression of WUS expression and termination of floral stem cell fate. We show that AG directly represses WUS expression by binding to the WUS locus and recruiting, directly or indirectly, PcG that methylates histone H3 Lys-27 at WUS. We also show that PcG acts downstream of AG and probably in parallel with the known AG target KNUCKLES to terminate floral stem cell fate. Our studies identify core components of the network governing the temporal program of floral stem cells.

BACKGROUND & AIMS Chronic hepatitis C virus infection activates an intrahepatic immune response, leading to increased expression of interferon (IFN)-stimulated genes and activation of natural killer (NK) cells—the most prevalent innate immune cell in the liver. We investigated whether the elimination of HCV with direct-acting antiviral agents normalizes expression of IFN-stimulated genes and NK cell function. METHODS We used multicolor flow cytometry to analyze NK cells from liver and blood of 13 HCV-infected patients who did not respond to treatment with pegylated interferon and ribavirin. Samples were collected before and during IFN-free treatment with daclatasvir and asunaprevir therapy and compared with those from blood of 13 healthy individuals (controls). Serum levels of CXCL10 and CXCL11 were measured by ELISA. RESULTS Before treatment, all patients had increased levels of CXCL10 or CXCL11 and a different NK cell phenotype from controls, characterized by increased expression of HLA-DR, NKp46, NKG2A, CD85j, pSTAT1, STAT1, and TNF-related apoptosis-inducing ligand (TRAIL). NK cells from patients also had increased degranulation and decreased production of IFNγ and TNFα compared with NK cells from controls. Nine patients had an end-of-treatment response (undetectable virus) and 4 had virologic breakthrough between weeks 4 and 12 of therapy. A rapid decrease in viremia and level of inflammatory cytokines in all patients was associated with decreased activation of intrahepatic and blood NK cells; it was followed by restoration of a normal NK cell phenotype and function by week 8 in patients with undetectable viremia. This normalized NK cell phenotype was maintained until week 24 (EOT). CONCLUSIONS DAA-mediated clearance of HCV is associated with loss of intrahepatic immune activation by IFNα, indicated by decreased levels of CXCL10 and CXCL11 and normalization of NK cell phenotype and function.

The rational construction and operation of an ideal helical spring has been investigated. The infinite helices, [Ag(Py 2 O)]X (Py 2 O ) 3,3′-oxybispyridine; X -) NO 3 -, BF 4 -, ClO 4 -, and PF 6 -), have been constructed in high yield via cooperative effects of the skewed conformer of Py 2 O and the potential linear geometry of the N-Ag(I)-N bond. Crystallographic characterization reveals that the polymer framework is an ideal cationic cylindrical helix and that its counteranions are pinched in two columns inside the helix. The four anions have been exchanged for each other in an aqueous solution without destruction of the helical skeleton. In particular, [Ag(Py 2 O)]NO 3 prepared by the counteranion exchange can be isolated as crystals suitable for X-ray crystallography in water. The helical pitch is reversibly stretched via the counteranion exchange from 7.430(2) to 9.621(2) Å, and is exactly proportional to the volume of the anion guests. This pitch-tuning is attributed to subtle change in the nonrigid dihedral angles between two pyridyl groups around O and Ag atoms that act as hinges within the helical subunit. Thermal analyses indicate that the helical compounds are stable up to 231-332 °C in the solid state.

Mediator is a conserved multi-subunit complex known to promote the transcription of protein-coding genes by RNA polymerase II (Pol II) in eukaryotes. It has been increasingly realized that Pol II transcribes a large number of intergenic loci to generate noncoding RNAs, but the role of Mediator in Pol II-mediated noncoding RNA production has been largely unexplored. The role of Mediator in noncoding RNA production in plants is particularly intriguing given that plants have evolved from Pol II two additional polymerases, Pol IV and Pol V, to specialize in noncoding RNA production and transcriptional gene silencing at heterochromatic loci. Here, we show that Mediator is required for microRNA (miRNA) biogenesis by recruiting Pol II to promoters of miRNA genes. We also show that several well-characterized heterochromatic loci are de-repressed in Mediator mutants and that Mediator promotes Pol II-mediated production of long noncoding scaffold RNAs, which serve to recruit Pol V to these loci. This study expands the function of Mediator to include Pol II-mediated intergenic transcription and implicates a role of Mediator in genome stability.

Stem cells are crucial in morphogenesis in plants and animals. Much is known about the mechanisms that maintain stem cell fates or trigger their terminal differentiation. However, little is known about how developmental time impacts stem cell fates. Using Arabidopsis floral stem cells as a model, we show that stem cells can undergo precise temporal regulation governed by mechanisms that are distinct from, but integrated with, those that specify cell fates. We show that two microRNAs, miR172 and miR165/166, through targeting APETALA2 and type III homeodomain-leucine zipper (HD-Zip) genes, respectively, regulate the temporal program of floral stem cells. In particular, we reveal a role of the type III HD-Zip genes, previously known to specify lateral organ polarity, in stem cell termination. Both reduction in HD-Zip expression by over-expression of miR165/166 and mis-expression of HD-Zip genes by rendering them resistant to miR165/166 lead to prolonged floral stem cell activity, indicating that the expression of HD-Zip genes needs to be precisely controlled to achieve floral stem cell termination. We also show that both the ubiquitously expressed ARGONAUTE1 (AGO1) gene and its homolog AGO10, which exhibits highly restricted spatial expression patterns, are required to maintain the correct temporal program of floral stem cells. We provide evidence that AGO10, like AGO1, associates with miR172 and miR165/166 in vivo and exhibits “slicer” activity in vitro. Despite the common biological functions and similar biochemical activities, AGO1 and AGO10 exert different effects on miR165/166 in vivo. This work establishes a network of microRNAs and transcription factors governing the temporal program of floral stem cells and sheds light on the relationships among different AGO genes, which tend to exist in gene families in multicellular organisms.

Histone acetylation is a major epigenetic control mechanism that is tightly linked to the promotion of gene expression. Histone acetylation levels are balanced through the opposing activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Arabidopsis HDAC genes (AtHDACs) compose a large gene family, and distinct phenotypes among AtHDAC mutants reflect the functional specificity of individual AtHDACs. However, the mechanisms underlying this functional diversity are largely unknown. Here, we show that POWERDRESS (PWR), a SANT (SWI3/DAD2/N-CoR/TFIII-B) domain protein, interacts with HDA9 and promotes histone H3 deacetylation, possibly by facilitating HDA9 function at target regions. The developmental phenotypes of pwr and hda9 mutants were highly similar. Three lysine residues (K9, K14, and K27) of H3 retained hyperacetylation status in both pwr and hda9 mutants. Genome-wide H3K9 and H3K14 acetylation profiling revealed elevated acetylation at largely overlapping sets of target genes in the two mutants. Highly similar gene-expression profiles in the two mutants correlated with the histone H3 acetylation status in the pwr and hda9 mutants. In addition, PWR and HDA9 modulated flowering time by repressing AGAMOUS-LIKE 19 expression through histone H3 deacetylation in the same genetic pathway. Finally, PWR was shown to physically interact with HDA9, and its SANT2 domain, which is homologous to that of subunits in animal HDAC complexes, showed specific binding affinity to acetylated histone H3. We therefore propose that PWR acts as a subunit in a complex with HDA9 to result in lysine deacetylation of histone H3 at specific genomic targets.SANT domain | POWERDRESS | HDA9 | histone deacetylation | AGL19 P osttranslational modifications of histones-including acetylation, methylation, phosphorylation, and ubiquitinationplay important roles in plant development, genome integrity, and stress responses. Histone acetylation/deacetylation, a reversible process, promotes/represses gene expression (1) and occurs at lysine residues within histone N-terminal tails. The histone acetylation status is regulated by counteracting enzymes: histone acetyltransferases (HATs) and histone deacetylases (HDACs). The 18 HDACs identified in Arabidopsis (2) can be categorized into three groups based on phylogenetic analysis: reduced potassium dependency-3/histone deacetylase-1 (RPD3/HDA1), histone deacetylase-2 (HD2), and silent information regulator-2 (SIR2)-like (3). Twelve HDACs belong to the RPD3/HDA1 group (3) and are involved in various biological processes, such as organ development, reproductive processes, hormone signaling, and DNA methylation (4-9). They can be further classified into three classes based on sequence homology (3). The HD2 group is plant-specific and includes four HDACs that act in plant development and stress responses (10-13). The two HDACs encoded by the SIR2 family genes in Arabidopsis, SRT1 and SRT2, regulate mitochondrial energy metabolism and cellular dedifferentiation, respectively (14,15).I...

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We synthesized highly crystalline zinc telluride (ZnTe) nanocrystals with a controlled shape using various growth conditions. The following amines were used as activation agents for the zinc precursor: zinc stearate, octylamine (OA), dodecylamine (DDA), octadecylamine (ODA), and trioctylamine (TOA). Unique 3-D nanoflowers (av size ) 20-120 nm) that consisted of a number of nanodots (av size ) 4-11 nm) were efficiently produced when no amine or TOA was used. Dispersed nanodots were produced when OA, DDA, or ODA were used. These results indicate that the steric effect of alkyl chains plays an important role in the formation of nanoflowers. Furthermore, the shape evolution from nanoflowers to nanorods occurred at higher growth temperatures, and nanoflowers and nanorods eventually evolved into nanodots after incubation.