Phosphorylation of the movement protein TGBp1 of Potato virus X by a CK2-like protein kinase is necessary for systemic infection

MÓDENA N; ZELADA A.; CONTE F; BINAGHI M AND MENTABERRY AN.

Beijing, China

Congreso; International Congress on Plant Tissue Culture and Biotechnology; 2006

International Association for Plant Tissue Culture and Biotechnology

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 (CP). The principal role of MPs is to assist in the spreading of viral progeny from cell to cell and over long distances. Mounting evidence suggests that phosphorylation events can regulate MP functions. In the present work we demonstrate that PVX TGBp1 is phosphorylated on serine and threonine residues by a kinase present in both PVX-infected and non-infected Nicotiana tabacum. This kinase activity presents characteristics of casein kinase CK2: it is inhibited by heparin and activated by polylysine and is able to use both ATP and GTP as phosphoryl donors. We also show that TGBp1 can be phosphorylated by Nicotiana tabacum CK2 a subunit and by a partially purified N. tabacum CK2. In addittion, in situ phosphorylation assays show that native PVX TGBp1 is phosphorylated in plant extracts of PVX-infected plants by a CK2-like cellular kinase. Based on comparative analyses of potexvirus TGBp1 we have developed two different PVX mutants on threonine residues. Infection experiments show that the mutants are not able to produce systemic infection. These results show that TGBp1 is phosphorylated  by a host kinase closely related to CK2, and suggest that this phosphorylation might be important in PVX mobilization in infected plants.