The key micronutrient copper orchestrates broad-spectrum virus resistance in rice.

Copper is a critical regulator of plant growth and development. However, the mechanisms by which copper responds to virus invasion are unclear. We previously showed that SPL9-mediated transcriptional activation of adds a previously unidentified regulatory layer to the established ARGONAUTE (AGO18)-miR528- () antiviral defense. Here, we report that rice promotes copper accumulation in shoots by inducing copper transporter genes, including and , to counteract viral infection. Copper suppresses the transcriptional activation of by inhibiting the protein level of SPL9, thus alleviating miR528-mediated cleavage of transcripts to strengthen the antiviral response. Loss-of-function mutations in , , and caused a significant reduction in copper accumulation and plant viral resistance because of the increased SPL9-mediated transcription. Gain in viral susceptibility was mitigated when was mutated in the mutant background. Our study elucidates the molecular mechanisms and regulatory networks of copper homeostasis and the SPL9-miR528-AO antiviral pathway.