Plant microRNAs enter the scene of calcium signaling

Recent studies have identified the miRNA391/1432/4376 superfamily (miR391^S) in seed plants, which targets the 5' untranslated region (UTR) of mRNAs encoding autoinhibited Ca²⁺-ATPases (ACAs), a key component of calcium signaling. This superfamily includes miR391 in the Brassicaceae, miR4376 in the Solanaceae, and miR1432 in the Poaceae, all of which share a highly conserved 10-nucleotide (nt) core in their mature miRNA sequences. Notably, miR1432 in the Poaceae targets both ACA and mRNAs encoding calmodulin-like proteins, which are putative Ca²⁺ sensors. In this opinion article we highlight evidence revealing this miRNA superfamily's ancient origin, regulatory conservation, and sequence diversification linked to functional innovation. Consistent with the central role of calcium signaling, recent studies on Arabidopsis thaliana and rice suggest the broad implications of the ACA-targeting miRNAs in plant development, immunity, and abiotic stress responses.