Plant symptoms are derived from specific interactions between virus and host components. However, little is known about viral or host factors that participate in the establishment of systemic necrosis. Here, we showed that helper component proteinase (HCPro) encoded by Chilli veinal mottle virus (ChiVMV), could directly interact with catalase 1 (CAT1) and catalase 3 (CAT3) of Nicotiana tabacum (N. tabacum) in cytoplasm to facilitate viral infection. In vitro, the activities of CAT1 and CAT3 were inhibited by the interaction between HCPro and CATs. The C terminus of HCPro was essential for their interaction and also required for the decrease of enzyme activities. Interestingly, the mRNA and protein level of catalases were up regulated in N. tabacum plants in response to ChiVMV infection. N. tabacum plants with HCPro overexpression or CAT1 knockout were more susceptible to ChiVMV infection, which was similar to that in H2O2 pretreated plants, and the overexpression of CAT1 inhibited ChiVMV accumulation. Besides, neither CAT1 nor CAT3 could affect the RNA silencing suppression (RSS) activity of HCPro. Our results confirmed that the interaction between HCPro and catalase promoted the development of plant systemic necrosis. This work demonstrated a novel role of HCPro in virus infection and pathogenicity.

Small GTPases play critical roles in the regulation of plant growth and development. However, the mechanism of small GTPases in plant response to virus infection remains largely unknown. Here, a Rho-type GTPase NtRHO1 was identified as one of up-regulated genes after tobacco mosaic virus (TMV) infection. Subcellular localization of NtRHO1 showed that it was localized in the cytoplasm, plasma membrane as well as nucleus. Transient overexpression of NtRHO1 in Nicotiana benthamiana plants accelerated virus reproduction and led to more reactive oxygen species production. By contrast, silencing of NtRHO1 reduced the sensitivity of N. benthamiana plants to TMV-GFP. Further explorations showed that there existed a direct interaction between NtRHO1 and NtWRKY50, a positive regulator of N. benthamiana plants response to virus infection. Yeast one-hybrid and electrophoretic mobility shift assays showed that this regulation was related to NtWRKY50’s binding capacity to the WK-box of PR1 promoter, which was weakened by the interaction between NtRHO1 and NtWRKY50. Thus, the role of a novel small GTPase NtRHO1 in the plant-pathogen interaction was explored and its mechanism was proposed.

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