GmMMP9 confers resistance to soybean mosaic virus via interactions with SMV-6K1 and GmPsaN to induce a ROS response

Abstract Soybean mosaic virus (SMV) is a prevalent disease that significantly impacts soybean yield and quality. However, the current understanding of molecular mechanisms on soybean resistance to SMV remains limited. Here, we characterized 27 soybean matrix metalloproteinase (MMP) family members and reported the function and regulatory mechanisms of GmMMP9 in SMV resistance. Functional studies found that GmMMP9 overexpressing soybeans exhibited the enhanced resistance to SMV, while CRISPR/Cas9 mediated GmMMP9 homozygous mutants were more susceptible. DAB and trypan blue staining revealed that GmMMP9 conferred SMV resistance through the ROS production and programmed cell death triggered by hypersensitive response. Furthermore, we identified that GmMMP9 was involved in the endoplasmic reticulum (ER) stress induced by SMV via its interaction with SMV protein 6K1 (SMV-6K1). This interaction was abolished only when all four 6K1-interacting residues in GmMMP9 were mutated, suggesting that GmMMP9 inhibited SMV-6K1 function via a structural envelopment mechanism. RNA-seq analysis of GmMMP9 overexpressing, knock-out and WT plants infected with SMV revealed that several differentially expressed genes (DEGs) were involved in photosynthesis-related processes. Moreover, we found a photosystem I (PS I) reaction center subunit N (GmPsaN) interacted with GmMMP9. Silencing GmPsaN in GmMMP9 overexpressing lines, knock-out lines and WT plants led to a reduction in chlorophyll content, SOD activity, H2O2 levels and the transcription expression of ROS signaling genes, which demonstrated that this interaction affected PS I activity and thereby triggered a ROS response. Overall, our findings revealed GmMMP9 as a novel regulator of soybean resistance to SMV, and indicated the potential use for soybean molecular breeding.