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

Abstract

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 <i>miR528</i> adds a previously unidentified regulatory layer to the established ARGONAUTE (AGO18)-miR528-<i>L-ascorbate oxidase</i> (<i>AO</i>) antiviral defense. Here, we report that rice promotes copper accumulation in shoots by inducing copper transporter genes, including <i>HMA5</i> and <i>COPT</i>, to counteract viral infection. Copper suppresses the transcriptional activation of <i>miR528</i> by inhibiting the protein level of SPL9, thus alleviating miR528-mediated cleavage of <i>AO</i> transcripts to strengthen the antiviral response. Loss-of-function mutations in <i>HMA5</i>, <i>COPT1</i>, and <i>COPT5</i> caused a significant reduction in copper accumulation and plant viral resistance because of the increased SPL9-mediated <i>miR528</i> transcription. Gain in viral susceptibility was mitigated when <i>SPL9</i> was mutated in the <i>hma5</i> mutant background. Our study elucidates the molecular mechanisms and regulatory networks of copper homeostasis and the SPL9-miR528-AO antiviral pathway.