MUTATIONAL ANALYSIS OF THE MOVEMENT PROTEIN OF ODONTOGLOSSUM RINGSPOTVIRUS TO IDENTIFY A HOST-RANGE DETERMINANT

Tobacco mosaic virus (TMV) which contains the movement protein CMP) of odontoglossum ringspot tobamovirus (ORSV) in place of the TMV MP syst emically infects orchids but causes local infection in tobacco unless the carboxy-terminal 48 amino acids of the MP are deleted (C. A. Holt, C. A. Fenczik, S. J. Gasper, and R. N. Beachy; Virology, in press, 19 95), Frameshift mutations were created within the 3' end of the MP gen e that led to truncations of the ORSV MP by 11, 19, 28, 37, and 48 ami no acids; each of the mutant MP genes was inserted into the cloned cDN A of TMV in place of the TMV MP and infectious transcripts were produc ed, Virus containing mutant MPs were used to infect vanilla orchids, a systemic host of ORSV, and tobacco plants, Removal of 11 amino acids from the ORSV MP prevented spread of the chimeric virus in orchids whi le restoring the ability to cause a systemic infection on tobacco, Fur ther deletions of the MP affected the size of virus-induced necrotic l ocal lesions on tobacco cv, Xanthi NN and the systemic spread and accu mulation of virus in cv. Xanthi nn, a systemic host of TMV, However, e ach virus replicated to equivalent levels in protoplasts, A mechanism by which the ORSV MP limits the spread of the chimeric virus is propos ed.