How rhizobial accessory plasmids impact symbiotic negotiations
J. GRIFFITTS (1), P. Price (1), C. Harrison (1) (1) Brigham Young University, U.S.A.

In the Sinorhizobium-Medicago symbiosis, rhizobial cells invade nodules through extracellular infection threads and are deposited into nodule cells as undifferentiated intracellular bacteroids. The potential of these bacteroids to benefit the host is dependent on peptide-based signaling that has begun to be elucidated over the last several years: Hundreds of different nodule-specific cysteine rich (NCR) peptides are expressed by the plant and secreted to the bacteroid-containing compartments where the bacteroids subsequently differentiate and initiate nitrogen fixation. This presentation addresses how rhizobial genotype influences NCR peptide-induced bacteroid differentiation, and how accessory plasmids can have a dramatic effect on this process. Many Sinorhizobium accessory plasmids encode a highly conserved peptidase that cleaves NCR peptides and impedes the path to nitrogen fixation. The presentation will emphasize the interesting evolutionary history of this peptidase, as well as its functional interactions with both rhizobial and host genetic modifiers. This peptidase has allowed us to probe the subtle biochemical negotiations that culminate in diverse states of symbiotic compromise, and it promises to assist in the discovery of additional molecular components of this remarkable intracellular dialog.

Abstract Number: C13-1
Session Type: Concurrent