Symptom recovery is affected by Cucumber mosaic virus coat protein phosphorylation.

Cucumber mosaic virus induces specific recovery phenotype, namely cyclic mosaic symptoms on tobacco plants. We provide further evidence that besides the 2b suppressor protein, the coat protein (CP) also has a role in symptom recovery and it is connected to its phosphorylation. We analyzed the impact of the phosphorylated (S148D) and the non-phosphorylated (S148A) state of CP148 Ser on symptom formation, virion stability and the effect of CP and its mutants on 2b-mediated local GFP-silencing. We demonstrated that a single aa change could be responsible for preventing the recovery phenomenon as replacing the phosphorylatable Ser with Ala in the 148aa position abolishing the cyclic phenomenon. CP/S148A mutation equilibrates the accumulation of the virus during the infection both at RNA and protein level in N. tabacum L. cv Xanthi plants. In summary, we determined a regulatory effect of the CMV CP on the self-attenuation mechanism and downregulation of the suppressor effect of the 2b protein.