SummaryCopper (Cu) microRNAs are upregulated by Cu deficiency and mediate the post‐transcriptional downregulation of transcripts that encode Cu proteins, suggesting a role directly related to Cu. However, expression and phenotypic analyses of copper microRNA mutants and over‐expressors have suggested roles mainly in tolerance to abiotic stresses. To reconcile available data, a model is proposed which emphasizes the mobile nature of copper microRNA molecules in the regulation of Cu homeostasis. It is proposed that the Cu‐microRNA regulatory circuits are further co‐opted by plants to regulate both beneficial and pathogenic interactions with microbes. Further exploration of Cu‐microRNA functions that account for the cell‐to‐cell mobility should give novel insight into plant microbe interactions and the integration of micronutrition and development. Contents Summary 1030 I. 1030 II. 1030 III. 1031 IV. 1031 V. 1032 VI. 1033 VII. 1034 VIII. 1034 1034 1034