Poster: Plant Pathogen/Symbiont Interactions

Abs # 707: Molecular evidence for auxin signaling in a nodulating legume

Presenter:	Knowlton, Anne L, kanne@clemson.edu
Authors	Knowlton, Anne L (A)   Schnabel, Elise  (A)   Frugoli, Julia A (A)
Affiliations:	(A): Clemson University

The nodulation of legumes by rhizobia involves molecular communication between the plant and the bacterium in order to establish a symbiotic relationship. Several lines of evidence suggest that, on the plant side of the symbiosis, auxin signaling occurs in the roots of legumes during nodulation. In order to explore this signaling, we took advantage of molecular tools developed in Arabidopsis to explore auxin-related gene expression during nodulation in the model legume Medicago truncatula. We transformed wild type M. truncatula roots with an Arabidopsis pIAA7::GUS promoter fusion (gift of Jason Reed) carried by A. rhizogenes to produce transgenic hairy roots. IAA7 is part of a large gene family whose members are rapidly induced by auxin and whose activity is tied to protein degradation through a ubiquitin-proteosome pathway. When roots carrying the fusion were grown for 3 weeks in the absence of rhizobia, GUS expression was detected in the vasculature of the root, but did not extend to the root tip and an unusual pattern of staining occurred in emerging lateral roots. When grown in the presence of rhizobium and evaluated through a time course of early nodulation events, GUS expression was observed in a pattern of regular striations on nodulating roots, while GUS expression in roots not responding to rhizobia remained unchanged. Expression of the pIAA7::GUS fusion was also characterized in roots of a mutant, sunn, which confers a supernodulation phenotype. This work was supported by an ASPB Undergraduate Research Fellowship.