βC1 encoded by tomato yellow leaf curl China betasatellite forms multimeric complexes in vitro and in vivo

The βC1 protein encoded by betasatellites associated with begomoviruses is multi-functional. To investigate its properties, the βC1 protein encoded by tomato yellow leaf curl China betasatellite (TYLCCNB) was expressed in Escherichia coli and analyzed for its ability to self-interaction. The βC1 protein formed large soluble multimeric complexes in vitro and in vivo. Mutations that prevented formation of multimeric complexes in vitro, also prevented formation of granular bodies in vivo, suggesting that granular bodies resulted from βC1 oligomerization. Similarly, βC1 mutants unable to form complexes also did not induce typical symptoms in plants when expressed from a Potato virus X (PVX) vector, suggesting that βC1 self-interaction was required for symptom induction in planta. Deletion analysis revealed that amino acid sequences spanning two predicted α-helices at the C-terminal end of the protein were important in multimerization.