Evaluation of Potato virus X mild mutants for cross protection against severe infection in China
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RESEARCH
Open Access
Evaluation of Potato virus X mild mutants for cross protection against severe infection in China Q. Q. Cong1,2,3†, Y. Wang1†, J. Liu1†, Y. F. Lan3, Z. K. Guo4, J. G. Yang2, X.-D. Li1*
and Y. P. Tian1*
Abstract Background: Cross protection is a promising alternative to control plant viral diseases. One critical factor limiting the application of cross protection is the availability of attenuated mutants or mild strains. Potato virus X (PVX) infects many crops and induces huge economic losses to agricultural production. However, researches on the variability and mechanism of PVX virulence are scarce. Methods: The mutants were obtained by introducing mutations into the RNA dependent RNA polymerase (RdRp) gene of PVX via site-directed mutagenesis. Attenuated mutants were screen according to their symptoms in Nicotiana benthamiana plants. The protection efficacy against severe infection were evaluated with interval of 5, 10 and 15 days. Results: Among the 40 mutants obtained, four mutants carrying substitutions of either Glu46, Asn863, Asn968 or Glu1001 to Ala in PVX RdRp showed drastically attenuated symptom, accompanying with reduced accumulation levels of coat protein, plus- and minus-sense RNAs. When the interval between protective and challenging inoculations was 15 days, mutant E1001A (with substitution of Glu1001 to Ala in RdRp) provided complete protection against severe infection in both Nicotiana benthamiana and tomato, while E46A (Glu46 mutated to Ala) provided incomplete protection. To reduce the risk of reverse mutation, we constructed mutant dM which carries double mutations of both Glu46 and Glu1001 to Ala in RdRp. The mutant dM could provide effective protection against severe PVX infection. Conclusion: Mutations of Glu46, Asn863, Asn968 or Glu1001 to Ala in PVX RdRp significantly reduced the viral symptoms. Mutants E1001A and E46A could provide effective protection against wild type PVX in both Nicotiana benthamiana and tomato. These results provide theoretical and practical bases for the control of PVX via cross protection. Keywords: Cross protection, Potato virus X, RNA dependent RNA polymerase, Virulence
Background Cross protection is a phenomenon in which plants infected or pre-inoculated with one virus with mild symptoms will show resistance to the subsequent infection by a severe isolate of the same or closely related virus [1–3]. It was first described with Tobacco mosaic virus (TMV) by McKinney in 1929 [4]. Since then, cross protection has * Correspondence: [email protected]; [email protected] † Q. Q. Cong, Y. Wang and J. Liu contributed equally to this work. 1 Shandong Province Key Laboratory of Agricultural Microbiology, Department of Plant Pathology, College of Plant Protection, Shandong Agricultural University, Tai’an, Shandong 271018, People’s Republic of China Full list of author information is available at the end of the article
been used to control viruses including Bean yellow mosaic virus [5], Citrus tristeza virus [6, 7], Clover yellow vein virus [5
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