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. 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. 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. 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.

Background: RNA-binding proteins (RBPs) participate in multiple aspects of RNA metabolism, which in turn regulates gene expression, thereby involving in organism growth and development. The UBA2 family, one of the subfamilies of RBPs, has been identified in several plant species. However, few researches have been performed to investigate the role of UBA2 in wheat (Triticum aestivum). Results: In this study, we identified eleven TaUBA2s and divided them into three groups according to their domain characteristics. Phylogenetic analysis was conducted to forecast functional similarities among Arabidopsis, rice, maize and wheat UBA2 genes. Members within the same subfamily of TaUBA2 are relatively conserved in terms of protein structure, motifs, and gene structure. Chromosomal location and synteny analysis suggested that the segmental duplication events played important roles during TaUBA2s evolution. The cis-acting element analysis showed that TaUBA2s were involved in hormone response, development, light response, metabolism, and response to environmental stress. Furthermore, TaUBA2C contains two RNA recognition motifs (RRMs), and the first RRM is responsible for the nuclear speckle formation of TaUBA2C, whereas the two RRMs are necessary for its biological function. Conclusions: Taken together, our study provides a comprehensive analysis of the TaUBA2 family in wheat and lays the foundation for the future functional investigations of TaUBA2s in wheat growth, development and stress responses.