Abstract
Plants respond to pathogen infection by activating signaling pathways leading to the accumulation of proteins with diverse roles in defense. Here, we addressed the functional role of PpPR-10, a pathogenesis-related (PR)-10 gene, of the moss Physcomitrella patens, in response to biotic stress. PpPR-10 belongs to a multigene family and encodes a protein twice the usual size of PR-10 proteins due to the presence of two Bet v1 domains. Moss PR-10 genes are differentially regulated during development and inoculation with the fungal pathogen Botrytis cinerea. Specifically, PpPR-10 transcript levels increase significantly by treatments with elicitors of Pectobacterium carotovorum subsp. carotovorum, spores of B. cinerea, and the defense hormone salicylic acid. To characterize the role of PpPR-10 in plant defense against pathogens, we conducted overexpression analysis in P. patens and in Arabidopsis thaliana. We demonstrate that constitutive expression of PpPR-10 in moss tissues increased resistance against the oomycete Pythium irregulare. PpPR-10 overexpressing moss plants developed less symptoms and decreased mycelium growth than wild type plants. In addition, PpPR-10 overexpressing plants constitutively produced cell wall depositions in protonemal tissue. Ectopic expression of PpPR-10 in Arabidopsis resulted in increased resistance against P. irregulare as well, evidenced by smaller lesions and less cellular damage compared to wild type plants. These results indicate that PpPR-10 is functionally active in the defense against the pathogen P. irregulare, in both P. patens and Arabidopsis, two evolutionary distant plants. Thus, P. patens can serve as an interesting source of genes to improve resistance against pathogen infection in flowering plants.
Highlights
Flowering plants have developed various defense strategies to cope with invading pathogens
To further analyze the PpPR-10-associated defense mechanisms resulting in increased disease resistance to P. irregulare, we focused on cell wall modifications, since we have previously shown that P. patens responds to this oomycete by reinforcing the cell walls (Oliver et al, 2009)
In wild type and PpPR-10 overexpressing lines H2O2 and superoxide accumulated after P. irregulare infection, no clear differences could be observed between the different genotypes (Supplementary Figure S4). These results indicate that PpPR-10 overexpression changes cell wall composition in protonemal tissues of P. patens, which could contribute to the increased resistance observed against P. irregulare in the overexpressing lines compared to wild type plants
Summary
Flowering plants have developed various defense strategies to cope with invading pathogens. Some of the genes involved in defense encode PR proteins (van Loon et al, 2006). PR proteins accumulate at the infection site in response to pathogen infection and contribute to systemic acquired resistance (SAR) (Ryals et al, 1996). These proteins are spread throughout the plant kingdom and divided into 17 classes (PR-1-17) on the basis of their amino acid sequence identity, biological activity or physicochemical properties (van Loon et al, 2006). Several members of the PR protein family have enzymatic activities, including β-1,3-glucanase (PR-2), chitinase (PR-3, -4, -8, and -11), peroxidase (PR-9) or endoproteinase (PR-7), and have shown to exhibit either antibacterial or antifungal activity (Edreva, 2005; van Loon et al, 2006)
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