C.T.R.M.P.I.C. · Cross Talk between Resistance Mechanisms to Pathogen Infection in Cereals

Final Activity Report Summary - C.T.R.M.P.I.C. (Cross Talk between Resistance Mechanisms to Pathogen Infection in Cereals)

The strategic objective of this fellowship was to understand important mechanisms associated to pathogen resistance that affect barley, one of the most important staple crops for consumers in the EU, for which fungicides, are indispensable at the moment. Moreover the knowledge gained on barley would be transferable to wheat and other grasses. In their natural environment plants are subject to simultaneous challenges by a variety of biotic and abiotic stresses. It was recently shown that these stimuli interfere with the outcome of RNA silencing-mediated defence mechanisms. During the course of this fellowship, we characterised the function of genes associated to pathogen resistance and susceptibility (leading to disease) using virus induced gene silencing. (1) A previously identified gene as a regulator of programmed cell death (Bax-Inhibitor 1, BI-1) was demonstrated to be involved in regulating basal resistance resulting in reduced penetration of fungal pathogen in a susceptible host plant following knock-down of BI-1 These results suggest that modification of BI-1 expression level affect plant cell homeostasis influencing cell death development and in some cases pathogen ingress. (2) We report the first evidence in monocots that, in addition to the previously described Sgt1, Rar1 and Hsp90 genes, a Receptor-Like Kinase (HvXa21-RLK) is a required component of the Mla13-mediated race-cultivar specific resistance. Contrasting cultivar specific expression patterns were observed with HvXa21RLK and others closely related RLKs during compatible and incompatible interactions suggest differential requirement of specific RLK for specific Mla-mediated resistance. Our data demonstrate that viral induced gene silencing is a powerful tool to characterise genes belonging to complex gene families involved in pathogen resistance in barley. (3) RNA-directed RNA polymerases (RDR) are not only involved in post-transcriptional gene silencing pathway but as well in mediating a potent antiviral response in plants. Our findings indicate a role in defence mechanism of endogenous RDRs in fungus infections as previously observed during viral infection. We identified a conserved expression pattern between species and an increased copy number of certain members of RDR gene family displaying contrasting expression patterns during pathogen infection and development in monocots. This suggests an evolutionarily directed genome duplication and selection for separate RDR functions by multiple gene members in monocot species. (4) Additonal milestone: A novel example of cross-talk between RNA-mediated defense and mRNA quality control machinery. Genes consist of coding and non-coding sequences known respectively as exons and introns. Intron needs to be spliced-out and other maturation processes has to be happen to generate a matured mRNA that will be recognised for initation of the translation process. RNAs that are improperly matured are perceived as aberrant. Such RNA failed to be translated into protein, and engage into a degradation process. We found that a so-called 'aberrant RNA' which do not contains all necessary splicing signals can be improperly maturated and subsequently becomes a target for degradation by endogenous quality control machinery. Further a plant cell use such aberrant RNA or its degradation products to mediate recognition and degradation of other RNA particles carrying the same sequence in the process identified as RNA interference. The new tool allows us to produce library of silencers made from mRNA expressed in cells / tissues / organisms in one step by simple ligation of cDNA library into designed ART-vector. ART-based library of silencer seems has the potential to become a very attractive tool to generate loss-of-function screen in plants and mammalian cells and illustrate another type of cross-talk between an endogenous RNA-mediated resistance mechanism and the quality control machinery associated with mRNA maturation.

Data: CORDIS, © European Union