Three PNAS papers explore DNA methylation and/or small RNAs in plant reproductive development. In angiosperms, sexual reproduction is accompanied by DNA demethylation in certain tissues, particularly those that have a nutritive or supporting role. Park et al. (10.1073/pnas.1619047114) show that in the endosperm this demethylation occurs on the chromosomes inherited from the central cell and requires DEMETER DNA demethylase. By contrast, DNA methylation is maintained in the gametes to ensure transmission of information across the generation. Hsieh et al. (10.1073/pnas.1619074114) show that pollen cells (both sperm cells and vegetative cells) have a greater efficiency of methylation maintenance than somatic cells. Finally, Fan et al. (10.1073/pnas.1619159114) show that photoperiod-sensitive male sterility (an important trait for hybrid seed production) is regulated by phased small-interfering RNAs (phasiRNAs), confirming that the phasiRNAs indeed have biological functions.
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