QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

Cover  Bacterial symbionts perturb and exploit the cellular functions of their eukaryotic hosts. On the left, a plant root (alfalfa, Medicago sativa) responds to the nitrogen-fixing symbiont bacteria, Sinorhizobium meliloti (see below).¹ A chemical signal from the bacterium causes the usually quiescent plant cells to re-initiate active cell division, giving rise to a root tumor. The bacteria provoke the plant to redirect the formation of the extracellular matrix to create a so-called "infection thread" (blue fluorescence). Infection threads are formed within the tips of epidermal root hairs and serve as channels for the bacterial invasion; the right panel shows a double infection in a single root hair cell (see below).² Bacteria within the infection thread, here labeled with GFP, grow and divide as they invade from within the plant. Genetic and biochemical studies by Sharon Long and her colleagues, together with work from other laboratories, have revealed that these early steps of bacteria/plant interaction occur by exchange of chemical signals between plants and symbionts. While some signals have been identified, others are inferred but not yet defined. New information from genomics, cellular imaging, and other approaches will show how cell division, extracellular matrix information, and the cytoskeleton are controlled by the bacterial invasion.Suzanne Pfeffer

REFERENCES
1)  Gage et al. (1966). Journal of Bacteriology. 178, 7159-7166. Reprinted with permission from the American Society for Microbiology.

2)  Long and Staskawicz. (1993). Cell. 73, 921-935. Reprinted with permission from Cell Press.