Identification by suppression subtractive hybridization and expression analysis of Medicago truncatula putative defence genes in response to Orobanche crenata parasitization

Crenate broomrape (Orobanche crenata) is the major constraint for pea and faba bean production in the Mediterranean region. In this study, a systematic sequencing of expressed sequence tags (ESTs) was chosen to obtain a first global picture of the assembly of genes involved in defence response. A cDNA-library was established by suppression subtractive hybridization in the model legume Medicago truncatula infected by O. crenata in order to identify a large number of host plant ESTs. Eighty-one presumably up-regulated genes were identified and classified in functional categories. EST-annotations showed homologies to a number of well-characterized genes. Most of the proteins encoded by these genes, are already known in defence in M. truncatula, such as genes related to the JA pathway or involved in cell wall modifications. A notable number of the ESTs, however, were derived from novel genes not matching entries of the large-scale M. truncatula sequences collections. Expression analyses by quantitative RT-PCR of 20 genes corresponding to different functional categories showed high expression levels, supporting their involvement in the defence response.