Two viral proteins translated from one open reading frame target different layers of plant defence

Multi-layered defence responses are activated upon pathogen attack. Viruses utilize a number of strategies to maximize the coding capacity of their small-sized genomes and produce viral proteins for infection, including suppression of host defence. Here, we uncover translation leakage as one of these strategies: two viral effectors, cC4 and mC4, encoded by tomato golden mosaic virus (TGMV) are translated from two in-frame start codons and function cooperatively to suppress defence. cC4 localizes in chloroplasts, to which it recruits NbPUB4 to induce ubiquitination of the outer membrane; as a result, this organelle gets degraded, and chloroplast-mediated defences are abrogated. However, chloroplast-localized cC4 induces the production of singlet oxygen ( 1212