Analysis of Medicago truncatula nodule expressed sequence tags

Systematic sequencing of expressed sequence tags (ESTs) can give a global p icture of the assembly of genes involved in the development and function of organs, Indeterminate nodules representing different stages of the develop mental program are especially suited to the study of organogenesis, With th e vector lambda HybriZAP, a cDNA library was constructed from emerging nodu les of Medicago truncatula induced by Sinorhizobium meliloti, The 5' ends o f 389 cDNA clones were sequenced, then these ESTs were analyzed both by seq uence homology search and by studying their expression in roots and nodules , Two hundred fifty-six ESTs exhibited significant similarities to characte rized data base entries and 40 of them represented 26 nodulin genes, while 133 had no similarity to sequences with known function. Only 60 out of the 389 cDNA clones corresponded to previously submitted M. truncatula EST sequ ences, For 117 cDNAs, reverse Northern (RNA) hybridization with root and no dule RNA probes revealed enhanced expression in the nodule, 48 clones are l ikely to code for novel nodulins, 33 cDNAs are clones of already known nodu lin genes, and 36 clones exhibit similarity to other characterized genes, T hus, systematic analysis of the EST sequences and their expression patterns is a powerful way to identify nodule-specific and nodulation-related genes .