Asuka Itaya,¹ Genqing Liang, ^{1, 2} Young-Min Woo,¹ Richard S. Nelson,³ and

Biao Ding ^{1, 2}

¹ Department of Botany, Oklahoma State University, Stillwater

² Department of Plant Biology, Ohio State University, Columbus

³ Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma

Plasmodesmata mediate intercellular transport of proteins, nucleic acids and small molecules in plants. We show that transiently-produced green fluorescent protein (GFP) trafficked intercellularly in epidermis of sink leaves, but not of source leaves in tobacco and cucumber. In contrast, the protein did not traffic in either sink or source leaves of tomato. On the other hand, the protein spread extensively from cell to cell in the epidermis of all leaves and stems of Arabidopsis thaliana as well as in young hypocotyls and cotyledons of tomato and cucumber. GFP could traffic from epidermis to ground tissues in hypocotyls, but not in cotyledons of cucumber. GFP fused to a number of mutant forms of the cucumber mosaic virus 3a movement protein (CMV 3a MP) failed to move from cell to cell, suggesting that GFP does not have a specific motif for plasmodesmal trafficking. Our data, together with previous findings, indicate that plasmodesmata can mediate both specific and nonspecific intercellular trafficking of proteins. Furthermore, our data suggest that nonspecific protein trafficking is controlled by species-, organ-, tissue-, and development-specific factors. Since GFP can readily traffic from cell to cell, it raises the questions of how metabolites are compartmentalized in a plant and of whether some endogenous plant proteins traffic nonspecifically from cell to cell to perform physiological functions yet to be elucidated.

References

Itaya, A., Liang, G., Nelson, R.S., and Ding, B. (2000). Nonspecific intercellular protein trafficking probed by green fluorescent protein. Protoplasma (In press).

Ding, B., Itaya, A., and Woo, Y.-M. (1999). Plasmodesmata and cell-to-cell communication in plants. Internatl. Rev. Cytol. 190:251-316.

Itaya, A., Woo, Y.-M., Masuta, C., Bao, Y., Nelson, R., and Ding, B. (1998). Developmental regulation of intercellular protein trafficking through plasmodesmata in tobacco leaf epidermis. Plant Physiol. 118:373-385.

Ding, B. (1998). Intercellular protein trafficking through plasmodesmata. Plant Mol. Biol. 38:279-310.

Itaya, A., Hickman, H., Bao, Y., Nelson, R. and Ding, B. (1997). Cell-to-cell trafficking of cucumber mosaic virus movement protein:green fluorescent protein fusion produced by biolistic gene bombardment in tobacco. Plant J. 12:1223-1230.