Tobacco necrosis virus replication and spread in Arabidopsis thaliana ecotype Columbia: a potential system for studying plant defense reactions to symptomless virus infections

Arabidopsis thaliana is susceptible to various different pathogens (fungi, bacteria, viruses). However, the effect of Tobacco necrosis virus (TNV) infection on Arabidopsis is not well known. TNV causes local necrotic and chlorotic lesions in the Arabidopsis ecotype Wassilewskija (Vannini et al., Physiol Mol Plant Pathol 69:26-42, 2006) but virus replication and systemic spread was not determined. Our goal was to monitor reactions to TNV infection in the most widely used A. thaliana ecotype, 'Columbia' (Col-0) by assessing in planta virus replication and systemic spread. We have shown that although TNV does not cause visible symptoms in A. thaliana ecotype Col-0 it is capable of replicating in planta as determined by real-time RT-qPCR. TNV levels progressively increased in inoculated leaves up to 4 days after inoculation (DAI) with a further severalfold increase between 4 and 8 DAI. Back inoculation of Nicotiana benthamiana resulted in symptoms typical of TNV infection (i.e., local necrotic lesions) within a few days. Interestingly, only a very low TNV titer (i.e., less than 20 % of that found in inoculated leaves) was detectable in non-inoculated upper leaves of Arabidopsis Col-0 even in an advanced stage of pathogenesis (21 DAI). The almost complete absence of systemic spread suggested that the virus is not seed-transmissible which was confirmed by real-time RT-qPCR analysis of plants grown from seeds produced by TNV-infected individuals. The present study is the first to show that TNV can infect the most widely used A. thaliana ecotype, Col-0, providing a novel system for future research on plant defense mechanisms during symptomless virus infections.