The proxiome of a plant viral protein with dual targeting to mitochondria and chloroplasts revealed MAPK cascade and splicing components as proviral factors

Abstract

The coat protein (CP) of the melon necrotic spot virus (MNSV) is a multifunctional factor localized in the chloroplast, mitochondria, and cytoplasm, playing a critical role in overcoming plant defenses such as RNA silencing (RNAi) and the necrotic hypersensitive response. However, the molecular mechanisms through which CP interferes with plant defenses remain unclear. Identifying viral–host interactors can reveal how viruses exploit fundamental cellular processes and help elucidate viral survival strategies. Here, we employed a TurboID-based proximity labeling approach to identify interactors of both the wild-type MNSV CP and a cytoplasmic CP mutant lacking the dual transit peptide (ΔNtCP). Of the interactors, eight were selected for silencing. Notably, silencing MAP4K SIK1 and NbMAP3Kε1 kinases, and a splicing factor homolog NbSMU2 significantly reduced MNSV accumulation, suggesting a proviral role for these proteins in plants. Yeast two-hybrid and bimolecular fluorescence complementation assays confirmed the CP and ΔNtCP interaction with NbSMU2 and NbMAP3Kε1 but not with NbSIK1, which interacted with NbMAP3Kε1. These findings open up new possibilities for exploring how MNSV CP might modulate gene expression and MAPK, thereby facilitating MNSV infection.