Role of phosphorylation on the silencing suppressor activity of the movement protein TGBp1 of the Potato X virus and the relationship with its ATPase activity

M. BINAGHI, N. MÓDENA, A. MENTABERRY, A. ZELADA

Quebec, Canadá

Congreso; XIV International Congress in Molecular Plant-Microbe Interactions; 2009

International Society of Molecular Plant-Microbe Interactions

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> Potato virus X (PVX) is a member of the potexvirus whose RNA genome codes for the viral replicase, three movement proteins (MPs: TGBp1, TGBp2 and TGBp3) and the viral capsid protein. Mounting evidence suggests that phosphorylation events can regulate MP functions. We have previously demonstrated that PVX TGBp1 is phosphorylated by a Nicotiana tabacum CK2-like kinase (Módena et al., 2008). The aim of this project is to evaluate the role of phosphorylation on the silencing suppressor and ATPase activities of the PVX TGBp1. Based on in silico analysis of sequences from different potexvirus TGBp1s, we identified two threonine residues possibly subjected to phosphorylation. We have developed different TGBp1 mutants where the identified threonines (T193 and T215) have been replaced by alanine (A) or aspartate (D) residues. Silencing experiments show that the TGBp1-T215A mutant is partially defective on its silencing suppressor activity whereas TGBp1-T215D loses all silencing suppressor activity. On the other hand, we observed that TGBp1-T193A has less suppressor activity due to the fact that it is less stable than wild-type TGBp1. We also show that although protein levels of TGBp1-T193D mutant are normal, it was not able to restore wild-type suppressor activity. Finally, ATP hydrolysis assays show that the ATPase activities of TGBp1-T193A and TGBp1-T215A were similar to wild-type TGBp1, whereas the revertant versions were significantly reduced. These results suggest that phosphorylation of PVX TGBp1 plays an important role in regulating the ATPase activity which might be necessary for silencing suppression.