Evidence for Proteolytic Processing of Tobacco Mosaic Virus Movement Protein in Arabidopsis thaliana. Richard K. Hughes. Department of Virus Research, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, U.K. Marie-Christine Perbal, Andrew J. Maule, and Roger Hull. Department of Virus Research, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, U.K. MPMI 8:658-665. Accepted 1 June 1995. Copyright 1995 The American Phytopathological Society.

Two ecotypes of Arabidopsis thaliana were transformed with the gene encoding tobacco mosaic virus (TMV) movement protein (P30). P30 accumulated largely in a subcellular Traction containing cell wall components and as a soluble protein. The protein migrated in denaturing gels with an Mr of 30K, significantly faster than P30 (Mr approximately 34K) accumulating after expression in transgenic tobacco, Escherichia coli or Spodoptera frugiperda cells, or after virus multiplication in tobacco. The P30 from A. thaliana infected with TMV for 14 days comigrated with that from E. coli, but that from A. thaliana infected for 49 days was of the smaller size. The use of antisera specific for the N- or C-termini of P30 showed that in A. thaliana P30 was proteolylically processed at the N-terminus, a region essential for P30 function. The failure of these plants to complement a TMV P30 mutant indicated that processed P30 was nonfunctional, although the processing was not so rapid that it prevented the development of systemic infections with wild type TMV. The absence of detectable P30 phosphorylation in A. thaliana demonstrated that phosphorylation was not essential for movement protein function and suggested that this species may use proteolytic cleavage of the N-terminus as an alternative strategy to tobacco for deactivating P30.