DNA methylation is an epigenetic modification required for transposable element (TE) silencing, genome stability, and genomic imprinting. Although DNA methylation has been intensively studied, the dynamic nature of methylation among different species has just begun to be understood. Here we summarize the recent progress in research on the wide variation of DNA methylation in different plants, organs, tissues, and cells; dynamic changes of methylation are also reported during plant growth and development as well as changes in response to environmental stresses. Overall DNA methylation is quite diverse among species, and it occurs in CG, CHG, and CHH (H = A, C, or T) contexts of genes and TEs in angiosperms. Moderately expressed genes are most likely methylated in gene bodies. Methylation levels decrease significantly just upstream of the transcription start site and around transcription termination sites; its levels in the promoter are inversely correlated with the expression of some genes in plants. Methylation can be altered by different environmental stimuli such as pathogens and abiotic stresses. It is likely that methylation existed in the common eukaryotic ancestor before fungi, plants and animals diverged during evolution. In summary, DNA methylation patterns in angiosperms are complex, dynamic, and an integral part of genome diversity after millions of years of evolution.

Seed, resulting from reproductive development, is the main nutrient source for human beings, and reproduction has been intensively studied through genetic, molecular, and epigenetic approaches. However, how different epigenetic pathways crosstalk and integrate to regulate seed development remains unknown. Here, we review the recent progress of epigenetic changes that affect chromatin structure, such as DNA methylation, polycomb group proteins, histone modifications, and small RNA pathways in regulating plant reproduction. In gametogenesis of flowering plants, epigenetics is dynamic between the companion cell and gametes. Cytosine DNA methylation occurs in CG, CHG, CHH contexts (H = A, C, or T) of genes and transposable elements, and undergoes dynamic changes during reproduction. Cytosine methylation in the CHH context increases significantly during embryogenesis, reaches the highest levels in mature embryos, and decreases as the seed germinates. Polycomb group proteins are important transcriptional regulators during seed development. Histone modifications and small RNA pathways add another layer of complexity in regulating seed development. In summary, multiple epigenetic pathways are pivotal in regulating seed development. It remains to be elucidated how these epigenetic pathways interplay to affect dynamic chromatin structure and control reproduction.

We have shown that the platelet counter-receptor for integrin Mac-1 (α_Mβ₂, CD11b/CD18) is glycoprotein (GP) Ibα, the largest component of the GP Ib-IX-V complex, better known for its role in mediating platelet attachment to sites of vessel wall injury. The GP Ibα-Mac-1 interaction mediates the firm adhesion of leukocytes on platelet thrombi, enabling their subsequent transmigration into the vessel wall. Our previous studies showed that the I-domain of Mac-1 binds the C-terminal flanking sequences (Phe201–Gly268) of GP Ibα, as demonstrated by the fact that binding is almost completely inhibited by the I domain ligands fibrinogen and heparin, the I-domain monoclonal antibody LPM19c, and the GP Ibα-specific monoclonal antibody AP1. The latter antibody is of interest because it also inhibits the binding of von Willebrand factor and thrombin. We have mapped the AP1 epitope to a 10-amino acid sequence spanning Arg218 to Tyr228. In the current investigation, we constructed a series of cell lines expressing mutants of human GP Ibα, either by replacement of the human sequence with the corresponding dog sequence (dog GP Ibα does not bind human Mac-1) or by targeted mutagenesis, and tested their ability to bind the recombinant Mac-1 I domain. The GP Ibα region Phe201-Asn223 was crucial for Mac-1 binding, with residues Arg218, Asp222 and Asn223 playing vital roles. In addition, a peptide containing the AP1 epitope (Leu214-Val229) bound Mac-1 I-domain specifically and saturably. Peptide binding was blocked by LPM19c and soluble GP Ibα, and by the M2 peptide, which corresponds to the GP Ibα-binding site in the Mac-1 I domain (Phe201-Lys217). Peptide binding was also blocked by an antibody against the M2 sequence. The AP1 peptide inhibited the attachment of GP Ib-IX-V complex-expressing CHO cells to immobilized Mac-1 I domain, and the adhesion of THP-1 cells—a monocytoid line expressing Mac-1—to immobilized GP Ibα. This peptide did not inhibit attachment of the cells VWF surfaces, or thrombin-induced platelet aggregation. In summary, we have defined the GP Ibα sequence Arg214 to Val229 as a critical binding site for Mac-1. Because a peptide corresponding to this region inhibits GP Ibα binding to Mac-1 but blocks neither platelet adhesion to immobilized VWF nor thrombin-induced platelet aggregation, it has potential to guide the development of agents that will specifically inhibit leukocyte-platelet complexes that promote vascular inflammation.