Abstract
The interaction between Arabidopsis thaliana and the oomycete pathogen Phytophthora parasitica emerges as a model for exploring the molecular basis and evolution of recognition and host defense. Phenotypic variation and genetic analysis is essential to dissect the underlying mechanisms in plant–oomycete interaction. In this study, the reaction phenotypes of 28 A. thaliana accessions to P. parasitica strain Pp016 were examined using detached leaf infection assay. The results showed the presence of four distinct groups based on host response and disease development. Of all the accessions examined, Zurich (Zu-1) is highly resistant to P. parasitica. Microscopic characterization showed that rapid and severe hypersensitive response at the primary infection epidermal cells is associated with disease resistance. Furthermore, Zu-1 is resistant to a set of 20 diverse P. parasitica strains, which were collected from different host plants and exhibited differential specificities on a set of tobacco cultivars. However, Zu-1 is susceptible to P. parasitica when the root is inoculated, suggesting differential expression of associated resistance genes in the root and foliar tissues. Genetic analysis by crossing Zu-1 and the susceptible accession Landsberg (Ler) showed that the resistance in Zu-1 to P. parasitica is semi-dominant, as shown by infection assays of F1 progenies, and is likely conferred by a single locus, defined as RPPA1Zu-1 (for Resistance to P. parasitica 1), as shown by analysis of F2 segregating populations. By employing specific-locus amplified fragment sequencing (SLAF-seq) strategy to identify molecular markers potentially linked to the locus, the strongest associated region was determined to be located between 7.1 and 11.2 Mb in chromosome IV. The future cloning of RPPA1Zu-1 locus will facilitate improved understanding of plant broad-spectrum disease resistance to oomycete pathogens.
Highlights
Oomycetes represent a group of eukaryotic microorganisms related to diatoms and brown algae, causing many destructive diseases to plants and animals (Beakes et al, 2012)
The results showed that the 48 accessions (Table 1) tested can be categorized into four distinct groups (N, Y, W, H) according to the resistance response, disease severity scored with water-soaked lesion size, development of abundant haustoria, and production of sporangia
Elucidation of the mechanism of the interaction between the pathogen and host plants has been the focus for understanding of disease resistance
Summary
Oomycetes represent a group of eukaryotic microorganisms related to diatoms and brown algae, causing many destructive diseases to plants and animals (Beakes et al, 2012). Unlike the well-studied species P. infestans, which is a foliage pathogen and only infected few plants, P. parasitica is a typical root pathogen with a broad-range of host plants, being capable of infecting over 72 plant genera (Meng et al, 2014). Nearly half of Phytophthora species are mostly pathogenic on roots, and about 30% species being pathogens of multiple host plants (Kroon et al, 2012). P. parasitica provides an opportunity for their role in understanding plant recognition and infection, and their broad host ranges. While being a natural pathogen of tobacco species, P. parasitica is capable of infecting the model plant species Arabidopsis thaliana, which allows accelerated understanding of Phytophthora pathogenesis and plant susceptibility (Attard et al, 2010; Wang et al, 2011)
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