DNA and histone methylation coregulate heterochromatin formation and gene silencing in animals and plants. To identify factors involved in maintaining gene silencing, we conducted a forward genetic screen for mutants that release the silenced transgene in the transgenic Arabidopsis () line We identified, which encodes methionine (Met) adenosyltransferase 4 (MAT4)/-adenosyl-Met synthetase 3 that catalyzes the synthesis of -adenosyl-Met (SAM) in the one-carbon metabolism cycle. mostly decreases CHG and CHH DNA methylation and histone H3K9me2 and reactivates certain silenced transposons. The exogenous addition of SAM partially rescues the epigenetic defects of SAM content and DNA methylation were reduced more in than in three other mutants. knockout mutations generated by CRISPR/Cas9 were lethal, indicating that is an essential gene in Arabidopsis. MAT1, 2, and 4 proteins exhibited nearly equal activity in an in vitro assay, whereas MAT3 exhibited higher activity. The native promoter driving ,, and cDNA complemented the mutant. However, most transgenic lines carrying native, , and promoters driving cDNA did not complement the mutant because of their lower expression in seedlings. Genetic analyses indicated that the double mutant is dwarfed and the double mutant was nonviable, while showed normal growth and fertility. These results indicate that MAT4 plays a predominant role in SAM production, plant growth, and development. Our findings provide direct evidence of the cooperative actions between metabolism and epigenetic regulation.

The R-loop, composed of a DNA-RNA hybrid and the displaced single-stranded DNA, regulates diverse cellular processes. However, how cellular R-loops are recognized remains poorly understood. Here, we report the discovery of the evolutionally conserved ALBA proteins (AtALBA1 and AtALBA2) functioning as the genic R-loop readers in Arabidopsis. While AtALBA1 binds to the DNA-RNA hybrid, AtALBA2 associates with single-stranded DNA in the R-loops in vitro. In vivo, these two proteins interact and colocalize in the nucleus, where they preferentially bind to genic regions with active epigenetic marks in an R-loop–dependent manner. Depletion of AtALBA1 or AtALBA2 results in hypersensitivity of plants to DNA damaging agents. The formation of DNA breaks in alba mutants originates from unprotected R-loops. Our results reveal that the AtALBA1 and AtALBA2 protein complex is the genic R-loop reader crucial for genome stability in Arabidopsis.

Epigenetic markers, such as histone acetylation and DNA methylation, determine chromatin organization. In eukaryotic cells, metabolites from organelles or the cytosol affect epigenetic modifications. However, the relationships between metabolites and epigenetic modifications are not well understood in plants. We found that peroxisomal acyl-CoA oxidase 4 (ACX4), an enzyme in the fatty acid β-oxidation pathway, is required for suppressing the silencing of some endogenous loci, as well as Pro35S:NPTII in the ProRD29A:LUC/C24 transgenic line. The acx4 mutation reduces nuclear histone acetylation and increases DNA methylation at the NOS terminator of Pro35S:NPTII and at some endogenous genomic loci, which are also targeted by the demethylation enzyme REPRESSOR OF SILENCING 1 (ROS1). Furthermore, mutations in multifunctional protein 2 (MFP2) and 3-ketoacyl-CoA thiolase-2 (KAT2/PED1/PKT3), two enzymes in the last two steps of the β-oxidation pathway, lead to similar patterns of DNA hypermethylation as in acx4. Thus, metabolites from fatty acid β-oxidation in peroxisomes are closely linked to nuclear epigenetic modifications, which may affect diverse cellular processes in plants.H istone acetylation is important for neutralizing the positive charges of lysine residues and promoting chromatin relaxation; it is also required for transcription, DNA replication, histone methylation, and other histone modifications (1-4). Histones are acetylated by acetyltransferases, which transfer acetyl groups from acetyl-CoA to histone lysine residues.Acetyl-CoA is a central metabolite that can be produced via several metabolic pathways involved in pyruvate, citrate, acetate, and fatty acid β-oxidation metabolism (5). In mammals, acetyl-CoA in mitochondria is produced from different pathways, including the fatty acid β-oxidation (6). In cytosol and nucleus, adenosine triphosphate (ATP)-citrate lyase (ACLY) cleaves citrate exported from mitochondria to regenerate acetyl-CoA that can be used for other biosynthetic processes, such as fatty acid synthesis and histone acetylation (6). In mouse, conditional loss of carnitine palmitoyltransferase 1A (CPT1A), which is required for the transfer of fatty acid into mitochondria for β-oxidation, impairs dermal lymphatic formation via histone acetylation in an ACLY-dependent manner (7). A pyruvate dehydrogenase complex can be translocated from mitochondria to nuclei to generate acetyl-CoA and mediate histone acetylation in mammalian cells in certain conditions (2,8). In Arabidopsis, the mutations in cytosolic acetyl-CoA carboxylase (ACC1), which converts cytosolic acetyl-CoA to malonyl-CoA for elongating the plastid-produced fatty acids, lead to high accumulation of cytosolic acetyl-CoA, specifically resulting in increased H3K27 acetylation (H3K27ac) (9).These results underscore the importance of acetyl-CoA in histone acetylation in nuclei in both mammals and plants. However, in plant cells, plastids, mitochondria, peroxisomes, and cytosol can produce acetyl-CoA (10). Whether impairment of metabolism ...

SiO2 films were deposited on fused silica, silicon, glass, germanium, and sapphire substrates by an ion beam sputtering technique. The optical properties of SiO2 films on different substrates and interfacial layer properties between SiO2 films and different substrates were researched by the spectroscopic ellipsometry technique. The refractive indices of SiO2 films deposited on different substrates are about 1.477 at the wavelength of 632.8 nm. The optical anisotropy property of SiO2 films on fused silica substrate is the best. The impact of thermal treatment on surface roughness and interfacial layer properties between SiO2 films and Si substrates were also investigated. When the annealing temperature is 550°C, the least surface thickness and thinnest interface layer thickness between v films and silicon substrate can be achieved. The results indicate that the surface and interface layer properties between SiO2 films and silicon substrate can be greatly improved when the optimum annealing temperature is selected.

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