Regulation and functional specialization of small RNA–target nodes during plant development

The expansion of gene families for miRNA and tasiRNA, small RNA effector proteins (ARGONAUTEs or AGOs), and miRNA/tasiRNA targets has contributed to regulatory diversity in plants. Loss or acquisition of small RNA-generating loci and target site sequences in multigene families represent striking examples of subfunctionalization or neo-functionalization, where regulatory diversity is achieved at the post-transcriptional level. Differential regulation of small RNA and target gene family members, and evolution of unique functionality of distinct small RNA–AGO complexes, provide further regulatory diversity. Here, we focus on the idea of distinct small RNA–target transcript pairs as nodes within biological networks, and review progress toward understanding the role of small RNA–target nodes in the context of auxin signaling.