Résumé
We created a network, called ARGEBIOS (Agropolis Reverse GEnetics for BlOtic Stress), of four laboratories involved in the area of resistance to biotic stress resistance in rice to collectively analyse compromised phenotypes of T-DNA tagged lines identified by reverse genetics approach. The ARGEBIOS integrated approach aims at identifying novel signalling and effector components involved in broad-spectrum resistance to biotic stress in rice and in specific pathways leading to resistance to bacterial, fungal and viral pathogens. Candidate genes were identified from transcriptome and proteome data generated in the four laboratories and from available data in the literature. Mutant T2 rice lines in candidate genes are analysed for compromised resistance to host and non-host rice pathogens and genotyped to verify the linkage between the identified phenotype and the T-DNA insertion. So far 150 mutant lines were analysed for compromised resistance to the three rice pathogens and non-host resistance to M. grisea a d mutant phenotypes were identified in up to 20% of T-DNA screened lines. C. Brugidou's team is studying the molecular interactions between rice and rice yellow mottle virus (RYMV) to elucidate the mechanisms controlling sensitivity, tolerance and the resistance of rice to the virus. Using a combined transcriptome, proteome and bioinformatic approach, they identified deregulation of host genome expression at the beginning of viral infection process. 550 genes were identified as highly deregulated in Indica and Japonica cultivars and are involved in all functional categories. They are using the ARGEBIOS set-up to functionally validate their implication in the viral infection processes. JB Morel's team is focusing on defining the signalling components involved in durable host resistance to M. grisea strains in both Japonica and Indica subspecies. The screen of T2 lines is based upon a compatible interaction enabling to reveal both EDS (enhanced disease susceptibility) and EDR (enhanced disease resistance) typ of mutants. P. Piffanelli's team interest lies on the mechanisms leading to cross-species non-host resistance to M. grisea strains in rice. A high-throughput inoculation protocol and phenotypic analysis for compromised non-host resistance of rice Nipponbare to M.grisea strains attacking other monocots (e.g. wheat, Digitaria, barley) was set-up at CIRAD to identify signalling components involved in type I and type II cross-species resistance mechanisms. V. Verdier's team focuses on the molecular mechanisms leading to resistance to bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo). Screening assays were performed on 30 day-old rice plants by leaf clip inoculation. Symptoms were scored by measuring lesion lengths. Most of the strains induced a susceptible reaction while strain PX0339 induced a moderate resistant reaction (MR) and was selected to screen the T-DNA mutants looking at EDS-type phenotypes. Mutant phenotypes were identified in 13% of T-DNA lines. We are now undergoing high-throughput g notyping of the identified lines following a protocol combining Southern blot and PCR analyses to confirm the linkage between T-DNA and observed phenotypes. The comparative study with fungal, bacterial and viral pathogens will enable to pinpoint shared signalling pathways likely to be potential targets to engineer durable field resistance to rice pathogens.