Function of ARGONAUTE proteins in the Arabidopsis shoot apical meristem (SAM).
In sexually propagating organisms, genetic and epigenetic mutations are evolutionarily relevant only if they occur in the germline and provide inherited information to the next generation. In contrast to most animals, plants are thought to lack an early segregating germline, implying that somatic cells can contribute genetic information to the progeny if they differentiate into meiocytes. Here we demonstrate that two ARGONAUTE proteins, AGO5 and AGO9, are expressed in the reproductive lineage throughout development and mark an early-segregating germline. Furthermore, both AGOs are loaded with dynamic populations of small RNAs derived from highly methylated, pericentromeric, long transposons. Sequencing single nuclei revealed that many of these transposons are highly expressed within a central stem cell domain. This indicates a host-parasite tug of war and specific silencing pathways in plant shoot apical meristems (SAMs). Our results open the path to investigate transposon biology and epigenome dynamics at cellular resolution in the SAM stem cell niche. Overall design: mRNA analysis of Stem Cell Domain