Abstract
BackgroundThe apoplast plays an important role in plant defense against pathogens. Some extracellular PR-4 proteins possess ribonuclease activity and may directly inhibit the growth of pathogenic fungi. It is likely that extracellular RNases can also protect plants against some viruses with RNA genomes. However, many plant RNases are multifunctional and the direct link between their ribonucleolytic activity and antiviral defense still needs to be clarified. In this study, we evaluated the resistance of Nicotiana tabacum plants expressing a non-plant single-strand-specific extracellular RNase against Cucumber mosaic virus.ResultsSevere mosaic symptoms and shrinkage were observed in the control non-transgenic plants 10 days after inoculation with Cucumber mosaic virus (CMV), whereas such disease symptoms were suppressed in the transgenic plants expressing the RNase gene. In a Western blot analysis, viral proliferation was observed in the uninoculated upper leaves of control plants, whereas virus levels were very low in those of transgenic plants. These results suggest that resistance against CMV was increased by the expression of the heterologous RNase gene.ConclusionWe have previously shown that tobacco plants expressing heterologous RNases are characterized by high resistance to Tobacco mosaic virus. In this study, we demonstrated that elevated levels of extracellular RNase activity resulted in increased resistance to a virus with a different genome organization and life cycle. Thus, we conclude that the pathogen-induced expression of plant apoplastic RNases may increase non-specific resistance against viruses with RNA genomes.
Highlights
The apoplast plays an important role in plant defense against pathogens
We have previously shown that tobacco plants expressing heterologous RNases are characterized by high resistance to Tobacco mosaic virus
We demonstrated that elevated levels of extracellular RNase activity resulted in increased resistance to a virus with a different genome organization and life cycle
Summary
The apoplast plays an important role in plant defense against pathogens. Some extracellular PR-4 proteins possess ribonuclease activity and may directly inhibit the growth of pathogenic fungi. Many plant RNases are multifunctional and the direct link between their ribonucleolytic activity and antiviral defense still needs to be clarified. Some extracellular S-like RNases and pathogenesisrelated protein 4 (PR-4) possessing ribonuclease activity are elevated both locally and systemically after wounding or pathogen invasion [4]. The expression patterns of both PR-4 and S-like RNase genes are rather complex and their participation in antiviral defense mechanisms is not yet clear. Non-plant extracellular RNases can be used as a tool to test the direct link between ribonucleolytic activity in the apoplast and resistance against RNA viruses. An elevated level of the heterologous extracellular RNase considerably increased the resistance level Based on these results and other indirect evidence, we conclude that apoplastic RNases participate in non-specific antiviral defense as part of plant non-host resistance mechanisms [11]
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