Abstract
Tomato yellow leaf curl China virus (TYLCCNV) is a monopartite begomovirus associated with different betasatellites. In this study, we investigate two different isolates of Tomato yellow leaf curl China betasatellite (TYLCCNB) to determine what features of the viral genome are required for induction of characteristic phenotypic differences between closely-related betasatellite. When co-agroinoculated with TYLCCNV into Nicotiana spp. and tomato plants, TYLCCNB-Y25 induced only leaf curling on all hosts, while TYLCCNB-Y10 also induced enations, vein yellowing, and shoot distortions. Further assays showed that βC1 of TYLCCNB-Y25 differs from that of TYLCCNB-Y10 in symptom induction and transcriptional modulating. Hybrid satellites were constructed in which the βC1 gene or 200 nt partial promoter-like fragment upstream of the βC1 were exchanged. Infectivity assays showed that a TYLCCNB-Y25 hybrid with the intact TYLCCNB-Y10 βC1 gene was able to induce vein yellowing, shoot distortions, and a reduced size and number of enations. A TYLCCNB-Y10 hybrid with the intact TYLCCNB-Y25 βC1 gene produced only leaf curling. In contrast, the TYLCCNB-Y25 and TYLCCNB-Y10 hybrids with swapped partial promoter-like regions had little effect on the phenotypes induced by wild-type betasatellites. Further experiments showed that the TYLCCNB-Y25 hybrid carrying the C-terminal region of TYLCCNB-Y10 βC1 induced TYLCCNB-Y10-like symptoms. These findings indicate that the βC1 protein is the major symptom determinant and that the C-terminal region of βC1 plays an important role in symptom induction.
Highlights
Geminiviruses are a group of plant viruses with single-stranded DNA genomes packaged in distinctive twinned particles
Consistent with the previous studies [4,6], in the presence of Tomato yellow leaf curl China betasatellite (TYLCCNB)-Y10, Tomato yellow leaf curl China virus (TYLCCNV) induced severe leaf curling and vein yellowing in all four host plants, and shoot distortion in N. benthamiana (Figure 1A) At the later stages of infection, enations could be observed in Nicotiana spp. (Figure 1B) and S. lycopersicum, with the highest number of enations present on N. benthamiana (Table 1)
S. lycopersicum plants (Figure 1C). These results suggest that the vein yellowing, shoot distortion, and enation phenotypes co-segregate with TYLCCNB-Y10
Summary
Geminiviruses (family Geminiviridae) are a group of plant viruses with single-stranded DNA genomes packaged in distinctive twinned particles. Sequence alignments showed that the reported betasatellites contain three common features: a satellite conserved region (SCR) adjacent to a putative stem-loop structure containing the nonanucleotide 51-TAATATTAC-31, a conserved complementary-sense gene (βC1), and an A-rich region located upstream of the βC1 gene that contributes to the size requirements for virus encapsidation and/or virus movement [5]. Using both transient expression and stable transformation systems, βC1 has been identified as a pathogenicity determinant as well as a suppressor of RNA silencing [6,7,8,9,10]
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