Dr. Manish Tiwari, Department of Bacteriology, University of Wisconsin-Madison, USA E-mail: mtiwari5@wisc.edu, will present a talk about his work on “Tracking the Ancestry of Nod Factors: Exploring the Realms Beyond Alpha- and Beta-Rhizobia”

The Abstract is as follows:

Nod factors produced by rhizobia were identified as lipo-chitooligosaccharides (LCOs) more than 30 years ago. These LCOs are required for intracellular infection and nodule organogenesis in most rhizobia-legume associations. The nature of substitutions on the LCO backbone is a significant determinant of host specificity in this symbiosis. About ten years ago, LCOs were also identified as produced by arbuscular mycorrhizal fungi. LCOs across rhizobia and fungi partly explain why several plant genes are required for LCO signal transduction and are involved in the common symbiotic pathway in legumes, affecting both root nodulation and mycorrhizal associations.

More recently, we demonstrated that LCOs are produced not only by arbuscular mycorrhizal fungi but by many fungi across the fungal kingdom (zygomycetes, ascomycetes, and basidiomycetes). These fungi exhibit various lifestyles as symbionts, pathogens, and saprotrophs; most are not associated with plants. We also demonstrated that many fungi respond to these LCOs in various dose-dependent ways, suggesting that LCOs could be fungal quorum-sensing-like molecules.

The presence of genes potentially allowing the production of LCOs has been reported in Frankia Cluster II bacteria. We identified such genes and demonstrated LCO production in several Gram-positive bacteria, such as Streptomyces bottropensis and Shimazuella kribbensis, that do not fix nitrogen or seem to associate with plants. We will present our current model for the origin and role of LCO production in fungi and bacteria.