Expression of the Movement Protein of Tobacco Mosaic Virus in the Cyanobacterium Anabaena sp. Strain PCC 7120. Marta Zahalak. Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121 U.S.A. Roger N. Beachy (2) and Teresa Thiel (1). (1) Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121 U.S.A. (2) The Scripps Research Institute, Department of Cell Biology, La Jolla, CA 92037 U.S.A. MPMI 8:192-199. Accepted 17 November 1994. Copyright 1995 The American Phytopathological Society.

The movement protein (MP) of tobacco mosaic virus (TMV) alters the structure and function of the plas-modesmata, the intercellular communication channels in plants. cDNA encoding the TMV MP was cloned in a cya-nobacterial shuttle vector and transferred to Anabaena sp. strain PCC 7120. MP was synthesized in Anabaena sp. strain PCC 7120 from the tac promoter and was induced severalfold by addition of the lac inducer IPTG. Immuno-blot analysis of subcellular fractions obtained from IPTG-induced vegetative cells indicated that MP was highly enriched in the cell wall and the cytoplasmic membrane fractions. High levels of MP expression prevented diazo-trophic growth and new heterocyst differentiation in cultures of Anabaena sp. strain PCC 7120. Although expression of MP in undifferentiated filaments did not inhibit growth, these filaments could not form heterocysts when subsequently deprived of combined nitrogen. Wild-type cells or cells containing the shuttle vector lacking the MP gene grew normally and differentiated heterocysts in the presence of IPTG. These results are consistent with the idea that interaction of MP with components in the cells of Anabaena sp. strain PCC 7120 perturbs normal cell-to-cell communication in the filaments, thereby preventing heterocyst differentiation and diazotrophic growth.