Roles for mannitol and mannitol dehydrogenase in active oxygen-mediated plant defense
D B Jennings1, M Ehrenshaft, D M Pharr
1Department of Horticultural Science, North Carolina State University, Raleigh, NC 27695-7609, USA.
Summary
Phytopathogenic fungi like Alternaria alternata use mannitol to suppress plant defenses. However, plants can counteract this by degrading fungal mannitol using mannitol dehydrogenase, a key defense mechanism.
Area of Science:
- Plant-pathogen interactions
- Plant immunity
- Fungal metabolism
Background:
- Reactive oxygen species (ROS) are crucial for plant defense signaling and pathogen resistance.
- Many fungi produce mannitol, a ROS scavenger, which can suppress ROS-mediated plant defenses.
- The interaction between fungal mannitol production and plant defense mechanisms is not fully understood.
Purpose of the Study:
- To investigate the role of mannitol in the interaction between the phytopathogenic fungus Alternaria alternata and host plants.
- To elucidate the plant's mechanism for counteracting fungal mannitol-mediated suppression of defense responses.
Main Methods:
- Induction of mannitol production and secretion in Alternaria alternata was analyzed in the presence of host-plant extracts.
- Expression of mannitol dehydrogenase, a mannitol-catabolizing enzyme, was studied in a non-mannitol-producing plant.
- Plant responses to fungal infection and defense inducers were assessed in relation to mannitol dehydrogenase activity.
Main Results:
- Alternaria alternata demonstrated induced mannitol production and secretion when exposed to host-plant extracts.
- A non-mannitol-producing plant showed induced mannitol dehydrogenase in response to fungal infection and plant defense elicitors.
- This suggests a plant-based counter-defense mechanism against fungal mannitol.
Conclusions:
- Plants can induce mannitol dehydrogenase to catabolize fungal-derived mannitol, thereby overcoming fungal suppression of ROS-mediated defenses.
- This study reveals a novel plant defense strategy involving the degradation of a fungal metabolite.
- Understanding this interaction is crucial for developing strategies to enhance plant resistance to fungal pathogens.
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