Local mechanical stimulation induces components of the pathogen defense response in parsley

Abstract

Cell suspension cultures of parsley (Petroselinum crispum) have previously been used as a suitable system for studies of the nonhost resistance response to Phytophthora sojae. In this study, we replaced the penetrating fungus by local mechanical stimulation by using a needle of the same diameter as a fungal hypha, by local application of a structurally defined fungus-derived elicitor, or by a combination of the two stimuli. Similar to the fungal infection hypha, the local mechanical stimulus alone induced the translocation of cytoplasm and nucleus to the site of stimulation, the generation of intracellular reactive oxygen intermediates (ROI), and the expression of some, but not all, elicitor-responsive genes. When the elicitor was applied locally to the cell surface without mechanical stimulation, intracellular ROI also accumulated rapidly, but morphological changes were not detected. A combination of the mechanical stimulus with simultaneous application of low doses of elicitor closely simulated early reactions to fungal infection, including cytoplasmic aggregation, nuclear migration, and ROI accumulation. By contrast, cytoplasmic rearrangements were impaired at high elicitor concentrations. Neither papilla formation nor hypersensitive cell death occurred under the conditions tested. These results suggest that mechanical stimulation by the invading fungus is responsible for the observed intracellular rearrangements and may trigger some of the previously demonstrated changes in the activity of elicitor-responsive genes, whereas chemical stimulation is required for additional biochemical processes. As yet unidentified signals may be involved in papilla formation and hypersensitive cell death.

The Powdery Mildew Disease of Arabidopsis: A Paradigm for the Interaction between Plants and Biotrophic Fungi

“…However, detailed analysis of the structures formed in response to non-biotic, mechanical wounds revealed that they are distinct in their composition and likely in their function from fungus-induced CWAs (Russo and Bushnell, 1989). In addition, no papilla formation was detected in response to mechanical (needle) stimulation of parsley suspension culture cells, despite detection of other responses associated with pathogen recognition such as reactive oxygen intermediates (ROI) production and induction of several elicitor-response genes (Gus-Meyer et al, 1998). Although there is no absolute association between papilla formation and resistance to fungal penetration, delayed formation of CWAs is correlated with enhanced fungal infection (Assaad et al, 2004).…”

Les liaisons dangereuses: immunological synapse formation in animals and plants

“…Because these experiments involved treatment of plant cells with a single stimulus, the flg22 peptide, it should be interesting to study FLS2 localization underneath surface colony-forming pathogenic Pseudomonas cells. Direct evidence that MAMP treatment alone is insufficient to induce the characteristic cell polarization process seen in bacterial interactions or those with filamentous parasites was demonstrated by co-stimulation experiments of individual plant cells with a MAMP from an oomycete pathogen (Pep-25) and mechanical stimulation using a needle of the same diameter as a fungal hypha [93]. Whereas mechanical stimulation alone induced polarized migration of intracellular organelles and the production of reactive oxygen intermediates (ROS), MAMP treatment induced ROS accumulation and the activation of a subset of defense-related genes [93].…”

“…Direct evidence that MAMP treatment alone is insufficient to induce the characteristic cell polarization process seen in bacterial interactions or those with filamentous parasites was demonstrated by co-stimulation experiments of individual plant cells with a MAMP from an oomycete pathogen (Pep-25) and mechanical stimulation using a needle of the same diameter as a fungal hypha [93]. Whereas mechanical stimulation alone induced polarized migration of intracellular organelles and the production of reactive oxygen intermediates (ROS), MAMP treatment induced ROS accumulation and the activation of a subset of defense-related genes [93]. However, co-stimulation triggered most of the early responses seen in interactions on fungal attack but was still insufficient to trigger papilla formation [93].…”

“…Whereas mechanical stimulation alone induced polarized migration of intracellular organelles and the production of reactive oxygen intermediates (ROS), MAMP treatment induced ROS accumulation and the activation of a subset of defense-related genes [93]. However, co-stimulation triggered most of the early responses seen in interactions on fungal attack but was still insufficient to trigger papilla formation [93]. This finding supports the idea that execution of polarized resistance responses in individual plant cells demands integration of stimulatory signals in much the same way as co-stimulation is needed for the establishment of a stable immunological synapse.…”

Non-self recognition, transcriptional reprogramming, and secondary metabolite accumulation during plant/pathogen interactions

“…The mechanical interaction has been experimentally decoupled from chemical signaling by replacing the hypha with a needle mimic. Even a gentle touch with a tungsten needle induces several, though not all, of the reactions observed after elicitor treatment or true infections, including the activation of some defense-related genes and the migration of nucleus and cytoplasm toward the site of physical contact (1).…”