ABSTRACT
Clones of tomato golden mosaic virus (TGMV), a key model for geminivirus research, have been transmitted back to their original host tomato for the first time. In contrast to the high pathogenicity in other solanaceous species, TGMV induced only very mild symptoms: a few chlorotic spots on the leaf lamina for the common variant (formerly strain cs), and limited vein yellowing for the yellow vein variant (yv). Symptoms disappeared over time, though viral DNA remained detectable in newly developed leaves. Both TGMV variants invaded phloem and, occasionally, also mesophyll parenchyma cells in tomato. Complete direct sequencing of rolling circle amplification products of the viral progeny in tomato plants revealed the consensus of the DNA populations for the two genome components (DNA-A, DNA-B) of both TGMV variants. The DNA-A components showed 98.5% and 99.9% nucleotide sequence identity, respectively, with the independently cloned TGMV molecule sequenced initially in 1984, confirming the classification of csTGMV and yvTGMV as variants. The results are discussed with reference to the history of the Brazilian "mosaico dourado" disease in tomato, and the odyssey of TGMV passaging through Nicotiana benthamiana plants and bacteria of numerous laboratories worldwide.
Subject(s)
Begomovirus/genetics , Begomovirus/pathogenicity , Cloning, Molecular , Plant Diseases/virology , Solanum lycopersicum/virology , Brazil , DNA, Viral/chemistry , DNA, Viral/genetics , DNA, Viral/isolation & purification , Plant Leaves/virology , Sequence Analysis, DNA , VirulenceABSTRACT
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.
