Plant chitinases have been known as pathogenesis-related (PR) proteins, but recent studies suggest that they play functional roles during normal plant growth and development. We previously isolated two cDNA clones encoding endochitinases, EuNOD-CHT1 and .CHT2, from the root nodules of Elaeagnus umbellata. These genes show differential expression patterns, with the EuNOD-CHT1 gene being active in the root nodules and meristems, while EuNOD-CHT2 is preferentially expressed in the infected cells of those nodules. To elucidate the functional roles of these two endochitinases, we have now constitutively expressed each gene in a heterologous plant system, Arabidopsis thaliana. Stable inheritance and expression of the transgenes were confirmed by genomic Southern hybridization and RT-PCR. Our transgenic plants did not differ morphologically from the wild types. However, constitutive expression of EuNOD-CHT1 and -CHT2 in Arabidopsis resulted in increased resistance against a fungal pathogen, Botrytis cinerea, but not against a bacterial agent, Pseudomonas syringae pv. Tomato DC3000. Expression levels were enhanced by both wounding and jasmonic acid treatments (for EuNOD-CHT1), or by jasmonic acid only (for EuNOD-CHT2). These data suggest that EuNOD-CHT1 and -CfiT2 primarily play defensive roles during root nodule development in E. umbellata.