Use of Differential Display to Identify Novel Sesbania rostrata Genes Enhanced by Azorhizobium cauiinodans Infection. Sofie Goormachtig . Laboratorium voor Genetica, Universiteit Gent, B-9000 Gent, Belgium. Marie Valerio-Lepiniec (1), Krzysztof Szczyglowski (2), Marc Van Montagu (1), Marcelle Holsters(1), and Frans J. de Bruijn (2,3). (1) Laboratorium voor Genetica, Universiteit Gent, B-9000 Gent, Belgium; (2) MSU-DOE Plant Research Laboratory, and (3) Department of Microbiology, Michigan State University, East Lansing 48824, U.S.A. MPMI 8:816-824. Accepted 8 August 1995. Copyright 1995 The American Phytopathological Society.

Upon infection of the tropical legume Sesbania rostrata with Azorhizobium cauiinodans ORS571, nodules are formed on the roots as well as on the stems. Stem nodules appear at multiple predetermined sites consisting of dormant root primordia, which are positioned in vertical rows along the stem of the plant. We used the differential display method to isolate and characterize three cDNA clones differential display; didi-2, didi-13, and didi-20), corresponding to genes whose expression is enhanced in the dormant root primordia after inoculation. Database searches revealed that the deduced (partial) didi-2 gene product shares significant similarity with hydroxypro-line-rich cell wall proteins. The (partial) didi-13 and didi-20 products are similar to chitinases and chalcone reductases, respectively. Transcripts corresponding to the cDNA clones didi-2 and didi-13 were first detectable 1 day after inoculation. In contrast, didi-20 transcripts were found at low levels in uninfected root primordia and were enhanced significantly around 3 days after inoculation. In addition, a cDNA was isolated (didi-42) that corresponds to the previously identified leghemoglobin gene Srlb6. These studies show that differential display is a useful method for the isolation of infection-related genes.