Howard, Jamie H. , Farruggia, Frank T. , Stepkowski, Tomasz , Wojciechowski, Martin F. .
Patterns in Legume Nod Factor Receptor Sequences Reflect Differences in Rhizobial Symbiont Specificity within Genus Sesbania Scop. (Leguminosae).
In the nitrogen-fixing symbiosis between legumes and rhizobia, the initial stage of recognition between the symbionts relies on interactions between the bacterial signaling molecule (the Nod factor) and the plant Nod factor receptor proteins (e.g., NFR1 and NFR5 in Lotus japonicus). There is considerable variation in host specificity exhibited by symbiotic bacteria. Some legumes are able to form nodules with multiple rhizobial genera while others with only one rhizobial strain. Mutagenic and transgenic experiments have shown that NFR5 in particular is instrumental in the recognition and selection of symbionts. We hypothesize that both changes to key amino acids in the extracellular portion of NFR5, where Nod factors may bind, and nfr5 gene duplication may influence symbiotic range. The tropical legume genus Sesbania is a good model to test these hypotheses. Based on molecular and morphological evidence, Sesbania is monophyletic with two major subclades, one composed of approximately 70 pantropically distributed species and another of six species endemic to the New World. Interestingly, constituent species within each subclade exhibit similar symbiotic ranges with regard to known rhizobial isolates. Using PCR, we obtained nfr5 sequences from 22 Sesbania species, including all six New World taxa, as well as from numerous outgroups. Southern blot hybridization was used to detect nfr5 gene duplication, and nodulation studies were conducted to confirm the symbiotic ranges of Sesbania species for which this information was unknown. Our results show that changes in amino acids at certain sites within the binding domains of NFR5 mirror changes in symbiotic patterns between the two Sesbania clades. Furthermore, we find evidence for nfr5 gene duplication that occurred early in legume evolution after lineages for subfamilies Caesalpinioideae and Papilionoideae diverged and that correlates with rhizobial specificity patterns in Sesbania.
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1 - Arizona State University, School of Life Sciences, P.O. Box 874601, Tempe, Arizona, 85287-4601, USA
2 - Arizona State University, School of Life Sciences, P.O. Box 874601, Tempe, Arizona, 85287, USA
3 - Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, Poznan, 61-704, Poland
4 - Arizona State University, School of Life Sciences, P.O. Box 874501, Tempe, Arizona, 85287-4501, USA
nod factor receptors
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Maybird/Cliff Lodge - Level C
Date: Monday, July 27th, 2009
Time: 9:00 AM