Plant Derived Glycoproteins and Glycolipids are Required for the Establishment of Functional Root-Microbe Symbiosis in Medicago truncatula    
W. MOORE (1), E. Rennie (1), H. Wipf (2), P. Hussey (1), E. Cahoon (3), J. Mortimer (1), H. Scheller (1) (1) Joint BioEnergy Institute, U.S.A.; (2) UC Berkeley, U.S.A.; (3) University of Nebraska, Lincoln, U.S.A.

Establishment of a functional plant-microbial symbiosis with arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing rhizobia is dependent on bi-directional signaling between host and symbiont. These signaling cascades lead to the development of specialized plant membranes that act as an interface between plant cells and their associated microbial liaisons, through which nutrients and information are exchanged. Arabinogalactan proteins (AGPs) have previously been reported through use of glycan-directed monoclonal antibodies to aggregate at the symbiotic interface in a variety of plant-microbe mutualisms. However, the identity of the genes encoding these glycoproteins has remained unknown. Here we report the discovery of several AGP encoding genes in Medicago truncatula that are specifically expressed during symbiosis with either AMF or Sinorhizobium meliloti. Functional studies using RNAi-mediated knockdown of specific AGPs result in drastic symbiotic phenotypes, including loss of arbuscule formation and impaired nitrogen fixation in root nodules. We have also identified a glycosyltransferase enzyme by co-expression analysis that, when silenced with RNAi, partially recapitulates the AGP phenotypes. Preliminary data suggest that this GT is involved in biosynthesis of glycosphingolipids, which are likely key components of the interface. Our data indicate that secretion of glycoproteins and glycolipids at the plant-microbial interface is imperative for functional symbiosis.

Abstract Number: P2-39
Session Type: Poster