Gene expression analysis of molecular mechanisms of defense induced in Medicago truncatula parasitized by Orobanche crenata.

The infection of Medicago truncatula Gaertn. roots with the obligate parasite Orobanche crenata Forsk. is a useful model for studying the molecular events involved in the legumes-parasite interaction. In order to gain insight into the identification of gene-regulatory elements involved in the resistance mechanism, the temporal expression pattern of ten defense-related genes was carried out using real-time quantitative reverse-transcription polymerase chain reaction assays. The induction of all of the analyzed transcripts significantly increased over a range from 2- to 321-fold higher than the control depending on the gene and time point. The transcriptional changes observed in response to O. crenata infection suggest that resistance could rely on both, the induction of general defense-related genes and more specific responses.

Protein cross-linking, peroxidase and beta-1,3-endoglucanase involved in resistance of pea against Orobanche crenata.

Root holoparasitic angiosperms, like Orobanche spp, completely lack chlorophyll and totally depend on their host for their supply of nutrients. O. crenata is a severe constraint to the cultivation of legumes and breeding for resistance remains the most economical, feasible, and environmentally friendly method of control. Due to the lack of resistance in commercial pea cultivars, the use of wild relatives for breeding is necessary, and an understanding of the mechanisms underlying host resistance is needed in order to improve screening for resistance in breeding programmes. Compatible and incompatible interactions between O. crenata and pea have been studied using cytochemical procedures. The parasite was stopped in the host cortex before reaching the central cylinder, and accumulation of H2O2, peroxidases, and callose were detected in neighbouring cells. Protein cross-linking in the host cell walls appears as the mechanism of defence, halting penetration of the parasite. In situ hybridization studies have also shown that a peroxidase and a beta-glucanase are differently expressed in cells of the resistant host (Pf651) near the penetration point. The role of these proteins in the resistance to O. crenata is discussed.