DNA methylation is an important feature of plant epigenomes, involved in the formation of heterochromatin and affecting gene expression. Extensive variation of DNA methylation patterns within a species has been uncovered from studies of natural variation. However, the extent to which DNA methylation varies between flowering plant species is still unclear. To understand the variation in genomic patterning of DNA methylation across flowering plant species, we compared single base resolution DNA methylomes of 34 diverse angiosperm species. By analyzing whole-genome bisulfite sequencing data in a phylogenetic context, it becomes clear that there is extensive variation throughout angiosperms in gene body DNA methylation, euchromatic silencing of transposons and repeats, as well as silencing of heterochromatic transposons. The Brassicaceae have reduced CHG methylation levels and also reduced or loss of CG gene body methylation. The Poaceae are characterized by a lack or reduction of heterochromatic CHH methylation and enrichment of CHH methylation in genic regions. Furthermore, low levels of CHH methylation are observed in a number of species, especially in clonally propagated species. These results reveal the extent of variation in DNA methylation in angiosperms and show that DNA methylation patterns are broadly a reflection of the evolutionary and life histories of plant species.

Reference methylomes provide insights into the evolutionary role of DNA methylation in paleopolyploid genomes.

Somatic embryogenesis is an important tissue culture technique that sometimes leads to phenotypic variation via genetic and/or epigenetic changes. To understand the genomic and epigenomic impacts of somatic embryogenesis, we characterized soybean (Glycine max) epigenomes sampled from embryos at 10 different stages ranging from 6 weeks to 13 years of continuous culture. We identified genome-wide increases in DNA methylation from cultured samples, especially at CHH sites. The hypermethylation almost exclusively occurred in regions previously possessing non-CG methylation and was accompanied by increases in the expression of genes encoding the RNA-directed DNA methylation (RdDM) machinery. The epigenomic changes were similar between somatic and zygotic embryogenesis. Following the initial global wave of hypermethylation, rare decay events of maintenance methylation were observed, and the extent of the decay increased with time in culture. These losses in DNA methylation were accompanied by downregulation of genes encoding the RdDM machinery and transcriptome reprogramming reminiscent of transcriptomes during late-stage seed development. These results reveal a process for reinforcing already silenced regions to maintain genome integrity during somatic embryogenesis over the short term, which eventually decays at certain loci over longer time scales.

Plant breeding has a long history of developing new varieties that have ensured the food security of the human population. During this long journey together with humanity, plant breeders have successfully integrated the latest innovations in science and technologies to accelerate the increase in crop production and quality. For the past two decades, since the completion of human genome sequencing, genomic tools and sequencing technologies have advanced remarkably, and adopting these innovations has enabled us to cost down and/or speed up the plant breeding process. Currently, with the growing mass of genomic data and digitalized biological data, interdisciplinary approaches using new technologies could lead to a new paradigm of plant breeding. In this review, we summarize the overall history and advances of plant breeding, which have been aided by plant genomic research. We highlight the key advances in the field of plant genomics that have impacted plant breeding over the past decades and introduce the current status of innovative approaches such as genomic selection, which could overcome limitations of conventional breeding and enhance the rate of genetic gain.

Soybean (Glycine max) and common bean (Phaseolus vulgaris) share a polyploidy event ~59 MYA, followed by a Glycine-specific whole genome duplication (WGD) ~8–13 MYA. Duplicated genes were classified into five categories: singletons, dispersed, proximal, tandem, or WGD/segmental and found strong correlations between gene category and functional annotation. Photosynthesis and transcriptional regulation-related Gene Ontology terms were significantly over-represented in singletons and WGD genes, respectively, aligning with the gene balance hypothesis. We found that the divergence of gene expression and DNA methylation between WGD-derived paralogs increased with age and that WGD genes, initially retained via dosage constraints, subsequently underwent expression divergence, associated with other factors such as DNA methylation. Genes derived from different modes of duplication differed in breadth, level, and specificity of expression in both species. Orthologous genes and ungrouped genes (genes not in an ortholog group) differed in expression patterns. The protein divergence rates of WGD paralog pairs containing an ungrouped gene were higher than those for which both copies had orthologs. We propose that many ungrouped genes are derived from divergent and redundant gene copies, concordant with the neofunctionalization hypothesis. Tandemly duplicated genes were distinct from WGD-derived genes, indicating that mode of duplication contributes to the evolutionary fate of duplicated genes.