Identification of Arabidopsis Loci Required for Susceptibility to the Downy Mildew Pathogen Hyaloperonospora parasitica

Abstract

Plants are susceptible to a limited number of pathogens. Most infections fail due to active defense or absence of compatibility. Many components of the plant's surveillance system and defense arsenal have been identified in the last decades. However, knowledge is limited on compatibility; in particular, the role of plant factors in the infection process. To gain insight into these processes, we have initiated an Arabidopsis thaliana mutant screen for reduced susceptibility to the downy mildew pathogen Hyaloperonospora parasitica. Ethyl methane sulfonate (EMS) mutants were generated in the highly susceptible Arabidopsis line Ler eds1-2. Eight downy mildew-resistant (dmr) mutants were analyzed in detail, corresponding to six different loci. Microscopic analysis showed that, in all mutants, H. parasitica growth was severely reduced. Resistance of dmr3, dmr4, and dmr5 was associated with constitutive expression of PR-1. Furthermore, dmr3 and dmr4, but not dmr5, also were resistant to Pseudomonas syringae and Golovinomyces orontii, respectively. However, enhanced activation of plant defense was not observed in dmr1, dmr2, and dmr6. We postulate that, in these susceptibility mutants, cellular processes are disrupted which are required for H. parasitica infection. This interesting new set of mutants provides a basis to elucidate the molecular processes underlying susceptibility to downy mildew in Arabidopsis.

Rationalization of genes for resistance to Bremia lactucae in lettuce

“…DMR6 in Arabidopsis is necessary for susceptibility to downy mildew; a recessive dmr6 allele derived by mutation results in resistance against Hyaloperonospora arabidopsidis (Van Damme et al 2005, 2008. A DMR6 ortholog has been identified in lettuce, where its over-expression increases host susceptibility to B. lactucae (Stassen et al 2012;Zeilmaker 2012).…”

Downy Mildew Resistance in Arabidopsis by Mutation of HOMOSERINE KINASE

“…Multiple independent alleles of dmr1, dmr1-1, dmr1-2, dmr1-3, and dmr1-4, were initially identified from a genetic screen for loss of susceptibility to H. arabidopsidis (Van Damme et al, 2005). These mutants were each backcrossed twice (BC 2 ) to the parental line Landsberg erecta (Ler) eds1-2 to reduce the number of unlinked ethyl methanesulfonate (EMS)-induced mutations.…”

“…Most of the pmr mutants are pathogen specific, reducing susceptibility to powdery mildew, but not to the bacterial pathogen Pseudomonas syringae and the downy mildew pathogen Hyaloperonospora arabidopsidis (Vogel and Somerville, 2000). Pathogen-specific resistance was also found for the Arabidopsis downy mildew resistant 1 (dmr1) mutant, which is resistant to H. arabidopsidis but susceptible to infection by other pathogens, for example, the powdery mildew fungus Golovinomyces orontii and P. syringae bacteria (Van Damme et al, 2005). The dmr1-mediated resistance to H. arabidopsidis could be due to the absence of a specific host protein required for infection or to a hitherto unknown defense mechanism.…”

Genetics and molecular mechanisms of resistance to powdery mildews in tomato (Solanum lycopersicum) and its wild relatives

“…In addition to the mlo and pmr mutants, a considerable number of S-genes have been identified in Arabidopsis (reviewed by Pavan et al 2010); e.g., downy mildew resistance (dmr1 to 6) mutants (Van Damme et al 2005). Based on studies on effectortriggerred susceptibility and by looking from a different point of view into host and non-host resistance (Fig.…”