Systematics Section / ASPT
Howard, Jamie H. , Wojciechowski, Martin F. .
A phylogenetic analysis of nuclear nfr5/sym10 Nod factor receptor gene sequences from the IR-lacking clade of papilionoid legumes (Fabaceae).
THE Inverted Repeat-Lacking Clade or "IRLC" of Fabaceae (Papilionoideae), is a large (ca. 4200 species) and diverse group of primarily temperate, herbaceous legumes which includes genera such as Pisum, Medicago, and Vicia. The majority of legumes engage in a symbiotic relationship with rhizobial bacteria initiated by a series of chemical cues: plants excrete flavonoids which induce the synthesis of bacterial Nod factors (lipochito-oligosaccharides), which in turn are recognized by plant receptors before the process of root infection and nodule formation. Unlike many legumes outside this clade, which generally exhibit a wide range of symbiont specificity, most species in the IRLC for which their symbionts are known exhibit very exclusive associations with specific rhizobial taxa. However, some IRLC members, such as species of Astragalus, are nodulated by a wide range of rhizobial strains. We are examining the phylogenetic utility of two recently identified, nuclear-encoded Nod factor receptor genes, which are critical to the initial steps of symbiont perception and recognition, to both clarify systematic relationships within this clade and to investigate the evolutionary pattern of host recognition and specificity between the symbiotic partners at the molecular level. Results from phylogenetic analyses (parsimony, maximum likelihood) of sequences from one of these plant receptor genes, nfr5 or sym10, corresponding to the conserved extracellular LysM domains of the protein, are highly congruent with those previously obtained using plastid matK/trnK and nuclear rDNA ITS sequences, and provide comparable nucleotide variation but better intraspecific resolution in some instances. Cloned sym10 genes from one genus, Astragalus, reveal multiple forms that could provide a greater diversity of receptors to expand a host plant's range of symbiont specificity. The study of plant and bacterial genes integral to the initiation of nodulation in legumes offers an opportunity to study the rhizobia-legume symbiosis from new evolutionary and molecular perspectives.
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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 874501, Tempe, Arizona, 85287-4501, USA
Nod factor receptor genes
Presentation Type: Poster:Posters for Sections
Location: Auditorium/Bell Memorial Union
Date: Tuesday, August 1st, 2006
Time: 12:30 PM