Study of the interactions between Arabis mosaic virus and its host plants

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Arabis mosaic virus (ArMV) belongs to the plant virus genus Nepovirus of the Secoviridae. In the wine producing areas southwest of Germany, including Neustadt an der Weinstrasse (NW), ArMV is, along with the Grapevine fanleaf virus (GFLV) and the Raspberry ringspot virus (RpRSV), two other nepoviruses, a causative agent of the grapevine fanleaf disease, one of the most widespread and damaging virus diseases affecting grapevine. ArMV is transmitted by the nematode vector Xiphinema diversicaudatum, and has a wide natural host range. Nepoviruses have two single-stranded positive sense genomic RNAs, which are linked to a VPg at their 5’ ends, and polyadenylated at their 3’ends. ArMV isolates from different hosts and geographical origins were mechanically inoculated onto Chenopodium quinoas. The symptoms obtained with ArMV-NW were very mild, whereas ArMV-Lilac and –Lv produced symptoms of different severity. To characterize the symptom determinant(s) encoded by ArMV, fragments corresponding to genes from both RNAs 1 and 2 of full-length infectious clones of ArMV-NW were exchanged by their counterpart of the ArMV-Lv or -Lilac isolates and tested by mechanical inoculations onto Chenopodium quinoa for their infectivity and functionality. The results obtained from the first set of clones showed the N-terminal protein of the protein 2A, the movement protein and the protein 1A are involved in the symptoms development. In Nicotiana benthamiana, the establishment rates of infection between ArMV-NW and -Lv differed, however the recovery phenomenon took place around the same time for both isolates, resulting in a disappearance of symptoms in ArMV-Lv-infected plants and a similarly low accumulation of viral RNAs for both isolates. Moreover, the ArMV-NW-recovered plants were not resistant to a secondary infection with ArMV-Lv. Post-Transcriptional Gene Silencing (PTGS) is an important antiviral defense system in plants. However, numerous viruses have developed a counter-defense strategy, by coding for a protein acting as a suppressor of gene silencing. So far, no suppressor of gene silencing has been identified for nepoviruses. The use of wild-type and GFP-transgenic Nicotiana benthamiana 16C for coinfiltration experiments via Agrobacterium tumefaciens of constructs containing the GFP and the different genes encoded by ArMV RNAs 1 or 2 allowed to identify the implication of NTB, VPg-Pro and/or VPg-Pro-Pol in the suppression of RNA silencing.