RNA viruses and their silencing suppressors boost Abutilon mosaic virus, but not the Old World Tomato yellow leaf curl Sardinia virus

Mixed viral infections can induce different changes in symptom development, genome accumulation and tissue tropism. These issues were investigated for two phloem-limited begomoviruses, Abutilon mosaic virus (AbMV) and Tomato yellow leaf curl Sardinia virus (TYLCSV) in Nicotiana benthamiana plants doubly infected by either the potyvirus Cowpea aphid-borne mosaic virus (CABMV) or the tombusvirus Artichoke mottled crinkle virus (AMCV). Both RNA viruses induced an increase of the amount of AbMV, led to its occasional egress from the phloem and induced symptom aggravation, while the amount and tissue tropism of TYLCSV were almost unaffected. In transgenic plants expressing the silencing suppressors of CABMV (HC-Pro) or AMCV (P19), AbMV was supported to a much lesser extent than in the mixed infections, with the effect of CABMV HC-Pro being superior to that of AMCV P19. Neither of the silencing suppressors influenced TYLCSV accumulation. These results demonstrate that begomoviruses differentially respond to the invasion of other viruses and to silencing suppression.

► Symptoms are aggravated in Nicotiana benthamiana plants doubly infected by phloem-limited begomoviruses (AbMV or TYLCSV) and by RNA viruses (poty- or tombusvirus). ► AbMV titer is increased in doubly infected plants, mainly with potyvirus, leading to AbMV occasional invasion of non-phloem tissue; TYLCSV titer is in most cases unaffected and this virus remains phloem-confined. No statistically significant differences were found in the number of begomovirus infected nuclei between singly or doubly infected plants. ► AbMV, but not TYLCSV, increases in plants expressing the silencing suppressor HC-Pro and, to a minor extent, P19; phloem evasion was not observed in this case for AbMV. ► Begomoviruses differ in sensitivity to co-infection by other viruses and respond differentially to silencing suppression.