article · Phytopathology
This research examines how the Rx1 gene confers symptomless, extreme resistance to Potato virus X in tobacco plants. The findings reveal that this immune response is driven by an early and intensive accumulation of the reactive oxygen species superoxide, which appears between one and six hours after viral inoculation and corresponds with heightened NADPH oxidase activity. When researchers chemically inhibited superoxide accumulation or genetically suppressed hydroxyl radicals, the plants lost their complete, symptomless immunity, showing elevated viral levels and necrotic tissue damage typical of a hypersensitive response. Applying a superoxide-generating compound to susceptible tobacco plants also decreased virus concentration while producing necrosis. Ultimately, extreme resistance uses rapid, transient bursts of reactive oxygen species to curb viral replication far earlier than standard hypersensitive immune responses.
Plant viruses cause substantial damage to agricultural yields. Understanding the specific chemical triggers that plants use to rapidly stop viruses without sustaining leaf tissue damage offers valuable insights for plant scientists. These findings demonstrate how specific reactive oxygen species directly restrict viral multiplication before visible damage or disease symptoms can manifest.
This work represents early-stage basic research into plant immune mechanisms. It provides biological insights that could inform crop protection strategies or plant breeding programmes targeting viral resistance. However, the abstract does not describe any specific agricultural product, field testing, or direct commercial application pathway.
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Here we show that in tobacco (<i>Nicotiana tabacum</i> cultivar Samsun NN <i>Rx1</i>) the development of <i>Rx1</i> gene-mediated, symptomless, extreme resistance to <i>Potato virus X</i> (PVX) is preceded by an early, intensive accumulation of the reactive oxygen species (ROS) superoxide (O<sub>2</sub>·<sup>-</sup>), evident between 1 and 6 h after inoculation and associated with increased nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activities. This suggests a direct contribution of this ROS to virus restriction during symptomless, extreme resistance. Superoxide inhibition in PVX-inoculated leaves by infiltration of antioxidants (superoxide dismutase [SOD] and catalase [CAT]) partially suppresses extreme resistance in parallel with the appearance of localized leaf necrosis resembling a hypersensitive resistance (HR) response. F<sub>1</sub> progeny from crosses of <i>Rx1</i> and ferritin overproducer (deficient in production of the ROS OH·) tobaccos also display a suppressed extreme resistance to PVX, because significantly increased virus levels are coupled to HR, suggesting a role of the hydroxyl radical (OH·) in this symptomless antiviral defense. In addition, treatment of PVX-susceptible tobacco with a superoxide-generating agent (riboflavin/methionine) results in HR-like symptoms and reduced PVX titers. Finally, by comparing defense responses during PVX-elicited symptomless, extreme resistance and HR-type resistance elicited by <i>Tobacco mosaic virus</i>, we conclude that defense reactions typical of an HR (e.g., induction of cell death/ROS-regulator genes and antioxidants) are early and transient in the course of extreme resistance. Our results demonstrate the contribution of early accumulation of ROS (superoxide, OH·) in limiting PVX replication during symptomless extreme resistance and support earlier findings that virus-elicited HR represents a delayed, slower resistance response than symptomless, extreme resistance.
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DOI: 10.1094/phyto-12-20-0540-r
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