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In plants, DNA methylation occurs in distinct sequence contexts, including CG, CHG, and CHH. Thus, plants have developed a surprisingly diverse set of DNA methylation readers to cope with an extended repertoire of methylated sites. The Arabidopsis genome contains twelve Methyl-Binding Domain proteins (MBD), and nine SET and RING finger-associated (SRA) domain containing proteins belonging to the SUVH clade, in addition to three homologs of UHRF1, namely VIM1-3, all containing SRA domains. In this review, we will highlight several research questions that remain unresolved with respect to the function of plant DNA methylation readers, which can have both de novo demethylase and maintenance activity. We argue that maintenance of CG methylation in plants likely involved actors not found in their mammalian counterparts, and that new evidence suggests significant reprogramming of DNA methylation during plant reproduction as an important new development in the field. Image 1 • Plants acquired DNA methylation readers to cope with a large repertoire of methylated sites. • This diversity is reflected throughout land plant evolution. • There are evidences for some level of conservation between animals and plants. • Plants have evolved unique features, including dedicated polymerases and plant-specific protein complexes. • Plant SUVH proteins can have both demethylase and methyltransferase activity. • CG maintenance in plants differs from the mammalian model, with VIM proteins bearing atypical motifs. [ABSTRACT FROM AUTHOR]

The life cycle of flowering plants is marked by several post-embryonic developmental transitions during which novel cell fates are established. Notably, the reproductive lineages are first formed during flower development. The differentiation of spore mother cells, which are destined for meiosis, marks the somatic-to-reproductive fate transition. Meiosis entails the formation of the haploid multicellular gametophytes, from which the gametes are derived, and during which epigenetic reprogramming takes place. Here we show that in the Arabidopsis female megaspore mother cell (MMC), cell fate transition is accompanied by large-scale chromatin reprogramming that is likely to establish an epigenetic and transcriptional status distinct from that of the surrounding somatic niche. Reprogramming is characterized by chromatin decondensation, reduction in heterochromatin, depletion of linker histones, changes in core histone variants and in histone modification landscapes. From the analysis of mutants in which the gametophyte fate is either expressed ectopically or compromised, we infer that chromatin reprogramming in the MMC is likely to contribute to establishing postmeiotic competence to the development of the pluripotent gametophyte. Thus, as in primordial germ cells of animals, the somatic-to-reproductive cell fate transition in plants entails large-scale epigenetic reprogramming. [ABSTRACT FROM AUTHOR]

Some angiosperms reproduce by apomixis, a natural way of cloning through seeds. Apomictic plants bypass both meiosis and egg cell fertilization, producing progeny that are genetic replicas of the mother plant. In this report, we analyze reproductive development in Tripsacum dactyloides, an apomictic relative of maize, and in experimental apomictic hybrids between maize and Tripsacum. We show that apomictic reproduction is characterized by an alteration of developmental timing of both sporogenesis and early embryo development. The absence of female meiosis in apomictic Tripsacum results from an early termination of female meiosis. Similarly, parthenogenetic development of a maternal embryo in apomicts results from precocious induction of early embryogenesis events. We also show that male meiosis in apomicts is characterized by comparable asynchronous expression of developmental stages. Apomixis thus results in an array of possible phenotypes, including wild-type sexual development. Overall, our observations suggest that apomixis in Tripsacum is a heterochronic phenotype; i.e., it relies on a deregulation of the timing of reproductive events, rather than on the alteration of a specific component of the reproductive pathway. [ABSTRACT FROM AUTHOR]