Activated malate circulation contributes to the manifestation of light-dependent mosaic symptoms.

Mosaic symptoms are commonly observed in virus-infected plants. However, the underlying mechanism by which viruses cause mosaic symptoms as well as the key regulator(s) involved in this process remain unclear. Here, we investigate maize dwarf mosaic disease caused by sugarcane mosaic virus (SCMV). We find that the manifestation of mosaic symptoms in SCMV-infected maize plants requires light illumination and is correlated with mitochondrial reactive oxidative species (mROS) accumulation. The transcriptomic and metabolomic analyses results together with the genetic and cytopathological evidence indicate that malate and malate circulation pathways play essential roles in promoting mosaic symptom development. Specifically, at the pre-symptomatic infection stage or infection front, SCMV infection elevates the enzymatic activity of pyruvate orthophosphate dikinase by decreasing the phosphorylation of threonine under light, resulting in malate overproduction and subsequent mROS accumulation. Our findings indicate that activated malate circulation contributes to the manifestation of light-dependent mosaic symptoms via mROS.