Although DNA N 6-adenine methylation (6mA) is best known in prokaryotes, its presence in eukaryotes has recently generated great interest. Biochemical and genetic evidence supports that AMT1, an MT-A70 family methyltransferase (MTase), is crucial for 6mA deposition in unicellular eukaryotes. Nonetheless, the 6mA transmission mechanism remains to be elucidated. Taking advantage of single-molecule real-time circular consensus sequencing (SMRT CCS), here we provide definitive evidence for semiconservative transmission of 6mA in Tetrahymena thermophila In wild-type (WT) cells, 6mA occurs at the self-complementary ApT dinucleotide, mostly in full methylation (full-6mApT); after DNA replication, hemi-methylation (hemi-6mApT) is transiently present on the parental strand, opposite to the daughter strand readily labeled by 5-bromo-2-deoxyuridine (BrdU). In ΔAMT1 cells, 6mA predominantly occurs as hemi-6mApT. Hemi-to-full conversion in WT cells is fast, robust, and processive, whereas de novo methylation in ΔAMT1 cells is slow and sporadic. In Tetrahymena, regularly spaced 6mA clusters coincide with the linker DNA of nucleosomes arrayed in the gene body. Importantly, in vitro methylation of human chromatin by the reconstituted AMT1 complex recapitulates preferential targeting of hemi-6mApT sites in linker DNA, supporting AMT1s intrinsic and autonomous role in maintenance methylation. We conclude that 6mA is transmitted by a semiconservative mechanism: full-6mApT is split by DNA replication into hemi-6mApT, which is restored to full-6mApT by AMT1-dependent maintenance methylation. Our study dissects AMT1-dependent maintenance methylation and AMT1-independent de novo methylation, reveals a 6mA transmission pathway with a striking similarity to 5-methylcytosine (5mC) transmission at the CpG dinucleotide, and establishes 6mA as a bona fide eukaryotic epigenetic mark.

Consumers and breeders value strawberry fruit with high sugar content and sweetness. However, many factors negatively affect this trait. bZIP-S1 subfamily was closely correlated with the carbohydrate metabolism. Moreover, it can regulate plant development and growth, and respond to various stress. In the present study, a total of four bZIP-S1 members were identified in strawberry. Quantitative RT-PCR analysis showed a member of this subfamily, designated as bZIP11, most highly expressed in different tissues of strawberry. Especially, it had a significant transcript accumulation during the fruit development and ripening. Constitutive expression of FvbZIP11 in tomato caused severe plant growth retardation which was accompanied by wrinkled and curly leaves. The leaf yellowish and chlorotic patches were reflected in decrease of chlorophyll. Meanwhile, epidermal cells were smaller in leaves of transgenic plant. In addition, the total soluble solid and soluble sugar content of the fruit was significantly higher than WT during the fruit ripening. Taken together, the heterologous overexpression of strawberry bZIP11 induced sugar accumulation and hindered plant growth in tomato, which provided more information for improving strawberry fruit quality.