Cucumber green mottle mosaic virus encodes additional small proteins with specific subcellular localizations and virulence function

This study is reported by Xueping Zhou and Fangfangli’s group from the Institute of Plant Protection, Chinese Academy of Agricultural Sciences (IPP, CAAS), Beijing. Like other positive-sense single-stranded RNA (+ssRNA), tobamoviruses have long been thought to encode proteins only in their positive strand (+RNA). This research provides novel insights into the coding capacity of the negative strand (-RNA) of tobamoviruses, challenging this long-held belief.

Their results uncover the existence of additional, previously overlooked small open-reading frames (rORFs) in the -RNA of tobamoviruses, using cucumber green mottle mosaic virus (CGMMV) and tobacco mosaic virus (TMV) as models. These rORFs were found to encode proteins with distinct subcellular localizations, such as peroxisomes and nucleoli. Additionally, these rORFs may utilize internal ribosome entry sites (IRES) for translation, which expands our current understanding of tobamovirus protein synthesis.

The authors further demonstrate that these novel rORFs play critical roles in viral infection. For example, CGMMV rORF1, which localizes to peroxisomes, interacts with viral replication-related proteins, and is essential for full viral virulence. Using a structure prediction tool ColabFold, the authors successfully identified PEX3 as a key peroxisomal protein (peroxin) interacting with rORF1, which mediates its targeting to peroxisomes.

In summary, this study reveals that the tobamovirus proteome is more extensive than previously recognized and uncovers peroxisomes as novel virulence targets critical for viral infection, which will need to be studied to gain a comprehensive understanding of viral infection.

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