Bacterial cell dynamics and molecular differentiation in symbiosis
S. LONG (1) (1) Department of Biology, Stanford University, U.S.A.

Symbiotic root nodulation occurs in a controlled series of bacterial and host transitions. Advances in genetics and genomics provide study systems allowing dissection of how symbiotic rhizobia communicate with their plant hosts at different stages. Initial searches for Sinorhizobium meliloti symbiosis genes used random transposon mutants that were individually screened on plants for Nod and Fix defects: such screens continue to yield new information! Promoter-trapping and transcriptomic analyses further identify genes active at specific developmental stages. We are presently collaborating in a systems-level project using Tn-seq to identify additional S. meliloti genes critical for symbiotic function. Host Medicago symbiosis mutants have helped to test relevant phenotypes such as the involvement of calcium signaling in nodulation, and in turn allow tests of individual plant gene function. We developed an S. meliloti reporter strain including differing FP or lacZ fusions to 4 genes active at distinct stages, which we use for screening new plant mutants. In a complementary strategy, we inoculated wild type bacteria onto plant mutants with symbiosis defects: using the bacterial transcriptome as a read-out of plant signaling, we identified three distinct transitions in bacteroid function that occur between release and Nif function. Advances in microscopy now allow us to connect the molecular and the cellular levels of cell behavior and plant-microbe interactions.

Abstract Number: OC
Session Type: Special Session