SET domains are conserved amino acid motifs present in chromosomal proteins that function in epigenetic control of gene expression. These proteins can be divided into four classes as typified by their Drosophila members E(Z), TRX, ASH1 and SU(VAR)3-9. Homologs of all four classes have been identified in yeast and mammals, but not in plants. A BLASTP screening of the Arabidopsis genome identified 37 genes: three E(z) homologs, five trx homologs, four ash1 homologs and 15 genes similar to Su(var)3-9. Seven genes were assigned as trx-related and three as ash1-related. Only four genes have been described previously. Our classification is based on the characteristics of the SET domains, cysteine-rich regions and additional conserved domains, including a novel YGD domain. RT-PCR analysis, cDNA cloning and matching ESTs show that at least 29 of the genes are active in diverse tissues. The high number of SET domain genes, possibly involved in epigenetic control of gene activity during plant development, can partly be explained by extensive genome duplication in Arabidopsis. Additionally, the lack of introns in the coding region of eight SU(VAR)3-9 class genes indicates evolution of new genes by retrotransposition. The identification of putative nuclear localization signals and AT-hooks in many of the proteins supports an anticipated nuclear localization, which was demonstrated for selected proteins.

SU(VAR)3-9 like histone methyltransferases control heterochromatic domains in eukaryotes. In Arabidopsis, 10 SUVH genes encode SU(VAR)3-9 homologues where SUVH1, SUVH2 and SUVH4 (KRYPTONITE) represent distinct subgroups of SUVH genes. Loss of SUVH1 and SUVH4 causes weak reduction of heterochromatic histone H3K9 dimethylation, whereas in SUVH2 null plants monoand dimethyl H3K9, mono-and dimethyl H3K27, and monomethyl H4K20, the histone methylation marks of Arabidopsis heterochromatin are significantly reduced. Like animal SU(VAR)3-9 proteins SUVH2 displays strong dosage-dependent effects. Loss of function suppresses, whereas overexpression enhances, gene silencing, causes ectopic heterochromatization and significant growth defects. Furthermore, modification of transgene silencing by SUVH2 is partially transmitted to the offspring plants. This epigenetic stability correlates with heritable changes in DNA methylation. Mutational dissection of SUVH2 indicates an implication of its N-terminus and YDG domain in directing DNA methylation to target sequences, a prerequisite for consecutive histone methylation. Gene silencing by SUVH2 depends on MET1 and DDM1, but not CMT3. In Arabidopsis, SUVH2 with its histone H3K9 and H4K20 methylation activity has a central role in heterochromatic gene silencing.

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Epigenetic reprogramming is at the base of cancer initiation and progression. Generally, genome-wide reduction in cytosine methylation contrasts with the hypermethylation of control regions of functionally wellestablished tumor suppressor genes and many other genes whose role in cancer biology is not yet clear. While insight into mechanisms that induce aberrant cytosine methylation in cancer cells is just beginning to emerge, the initiating signals for analogous promoter methylation in plants are well documented. In Arabidopsis, the silencing of promoters requires components of the RNA interference machinery and promoter double-stranded RNA (dsRNA) to induce a repressive chromatin state that is characterized by cytosine methylation and histone deacetylation catalysed by the RPD3-type histone deacetylase AtHDA6. Similar mechanisms have been shown to occur in fission yeast and mammals. This review focuses on the connections between cytosine methylation, dsRNA and AtHDA6-controlled histone deacetylation during promoter silencing in Arabidopsis and discusses potential mechanistic similarities of these silencing events in cancer and plant cells.

Substantial research effort has been dedicated to the electrochemical reduction of CO2 (CO2R) to higher carbon products throughout the recent years, baring the promise of a production pathway for green fuels and chemicals.1 However, only little progress has been achieved in the light driven heterogeneous CO2R catalysis, especially considering selective processes towards C2+ products. This arises from the additional complexity of photo-electrochemical reactions, which means that not only the sluggish reaction kinetics, high overpotentials and low selectivity of CO2R, but also the insufficient voltage and sensitivity towards harsh electrolyte conditions of photoabsorbers have to be encountered. Considering CO2R as multi-step process with CO as intermediate mitigates some issues of the process, e.g. the necessary overpotential is reduced and a higher selectivity towards valuable products can be achieved.2 Multi-junction solar stacks can provide operating voltages >2 V, which is sufficient for reducing CO2 to CO with high efficiencies or even produce multi-carbon products from CO while oxidizing water as anode reaction.3 In this work, we designed a process for photo-electrochemical CO reduction with multi-junction photoabsorbers. We start out by showing photo-electrochemical modelling of tandem photoabsorbers that emphasizes the advantages of CO as reactant compared to CO2. Further, we focus on the preparation of a nano-structured Cu catalyst, the most common material for reducing CO to C2+. Therefore, the electrochemical deposition and surface characterization using SEM, EDX and XPS of the catalyst on a dark model electrode coated with a sputter deposited TiO2 protection layer will be presented. Moreover, the CO reduction performance of the model at different potentials are characterized. In addition, the light transmission of the model electrode is reported, baring the possibility of illuminating the photoelectrode from the catalyst front side in mind. Lastly, the transfer of the model catalyst to a photoabsorber as well as the design of a photo-electrochemical flow-cell are discussed. Nitopi, S. et al. Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte. Rev. 119, 7610–7672 (2019)1. Wang, L. et al. Electrochemical Carbon Monoxide Reduction on Polycrystalline Copper: Effects of Potential, Pressure, and pH on Selectivity toward Multicarbon and Oxygenated Products. ACS Catal. 8, 7445–7454 (2018) Seger, B., Hansen, O. & Vesborg, P. C. K. A Flexible Web-Based Approach to Modeling Tandem Photocatalytic Devices. RRL 1, e201600013 (2017). Figure 1