LAUSR

DNA in plant male meiocytes is methylated by intercellular small interfering RNAs Plants produce 24-nucleotide (nt) small interfering RNAs (siRNAs) to maintain asymmetric DNA methylation in cis—that is, an siRNA will methylate DNA in the same region from which it is produced (1). However, 24-nt siRNAs also direct the methylation of DNA in trans to homologous loci (see the figure) and can move intercellularly to guide methylation in recipient cells (2). On page 76 of this issue, Long et al. (3) describe siRNAs from hundreds of loci that function both intercellularly and at nonallelic sites. Specifically, 24-nt siRNAs move from somatic cells to adjacent male germline cells (meiocytes). This joins a growing list of siRNA movements during plant reproductive development.