Ruf, A.; Thieron, H.; Nasfi, S.; Lederer, B.; Fricke, S.; Adeshara, T.; Postma, J.; Blumenkamp, P.; Kwon, S.; Brinkrolf, K.; Feldbrugge, M.; Goesmann, A.; Kehr, J.; Steinbrenner, J.; Secic, E.; Gohre, V.; Weiberg, A.; Kogel, K.-H.; Panstruga, R.; Robatzek, S.

RNA interference (RNAi) is a crucial mechanism that can contribute to immunity against infectious microbes through the action of DICER-LIKE (DCL) and ARGONAUTE (AGO) proteins. In the case of the fungal pathogen Botrytis cinerea and the oomycete Hyaloperonospora arabidopsidis, plant DCL and AGO proteins have proven roles as negative regulators of immunity, suggesting functional specialization of these proteins. To address this aspect in a broader taxonomic context, we characterized the colonization pattern of an informative set of DCL and AGO loss-of-function mutants in Arabidopsis thaliana upon infection with a panel of pathogenic microbes with different lifestyles, and a fungal mutualist. Our results revealed that AGO1 and AGO4 function as positive regulators of immunity to a bacterial and a fungal pathogen, respectively. Additionally, AGO2 and AGO10 positively modulated the colonization by a fungal mutualist. Therefore, analysing the role of RNAi across a broader range of plant-microbe interactions has identified previously unknown functions for AGO proteins. For some pathogen interactions, however, all tested mutants exhibited wild type-like infection phenotypes, suggesting that the roles of AGO and DCL proteins in these interactions may be more complex to elucidate.