A DNAβ Associated with Tomato Yellow Leaf Curl China Virus Is Required for Symptom Induction

Abstract

We report here that all 25 isolates of Tomato yellow leaf curl China virus (TYLCCNV) collected from tobacco, tomato, or Siegesbeckia orientalis plants in different regions of Yunnan Province, China, were associated with DNA␤ molecules. To investigate the biological role of DNA␤, full-length infectious clones of viral DNA and DNA␤ of TYLCCNV isolate Y10 (TYLCCNV-Y10) were agroinoculated into Nicotiana benthamiana, Nicotiana glutinosa, Nicotiana. tabacum Samsun (NN or nn), tomato, and petunia plants. We found that TYLCCNV-Y10 alone could systemically infect these plants, but no symptoms were induced. TYLCCNV-Y10 DNA␤ was required, in addition to TYLCCNV-Y10, for induction of leaf curl disease in these hosts. Similar to TYLCCNV-Y10, DNA␤ of TYLCCNV isolate Y64 was also found to be required for induction of typical leaf curl diseases in the hosts tested. When the ␤C1 gene of TYLCCNV-Y10 DNA␤ was mutated, the mutants failed to induce leaf curl symptoms in N. benthamiana when coinoculated with TYLCCNV-Y10. However, Southern blot hybridization analyses showed that the mutated DNA␤ molecules were replicated. When N. benthamiana and N. tabacum plants were transformed with a construct containing the ␤C1 gene under the control of the Cauliflower mosaic virus 35S promoter, many transgenic plants developed leaf curl symptoms similar to those caused by a virus, the severity of which paralleled the level of ␤C1 transcripts, while transgenic plants transformed with the ␤C1 gene containing a stop codon after the start codon remained symptomless. Thus, expression of a ␤C1 gene is adequate for induction of symptoms of viral infection in the absence of virus.

Tomato SlSnRK1 Protein Interacts with and Phosphorylates βC1, a Pathogenesis Protein Encoded by a Geminivirus β-Satellite

“…We demonstrated previously that TYLCCNV alone produces asymptomatic infections in tobacco, tomato, and petunia (Petunia hybrida) and that TYLCCNB is required for the production of leaf curl symptoms in these hosts (Cui et al, 2004). These studies showed that the bC1 protein encoded by TYLCCNB is a pathogenicity factor that is necessary for symptom production.…”

“…We demonstrated previously that transgenic N. benthamiana, tobacco, and Arabidopsis plants expressing the TYLCCNB bC1 gene are stunted and show leaf cupping and curling. The resulting "symptoms" are much more severe than those associated with TYLCCNV plus TYLCCNB infection, demonstrating that bC1 is very toxic to plants (Cui et al, 2004;Yang et al, 2008). SnRK1 phosphorylation of bC1 may be used by plants to overcome its detrimental effects.…”

“…Full-length b-satellite molecules encode an approximately 13.5-kD protein known as bC1 on the complementary sense strand. bC1 is a pathogenicity determinant and a suppressor of RNA silencing (Jose and Usha, 2003;Cui et al, 2004Cui et al, , 2005Saunders et al, 2004;Qian and Zhou, 2005;Saeed et al, 2005;Gopal et al, 2007;Kon et al, 2007). Previous studies showed that bC1 interacts with ASYMMETRIC LEAVES1 to alter leaf development and suppress selected jasmonic acid responses (Yang et al, 2008).…”

“…Begomoviruses have either monopartite or bipartite genomes (Hanley-Bowdoin et al, 2000;Fauquet et al, 2003). In recent years, a b-satellite molecule, which is a circular single-stranded DNA of approximately 1,350 nucleotides, has been associated with some monopartite begomoviruses, where it is essential for the induction of typical disease symptoms (Saunders et al, 2000(Saunders et al, , 2003Briddon et al, 2001;Jose and Usha, 2003;Cui et al, 2004). Full-length b-satellite molecules encode an approximately 13.5-kD protein known as bC1 on the complementary sense strand.…”

Replication promiscuity of DNA-β satellites associated with monopartite begomoviruses; deletion mutagenesis of the Ageratum yellow vein virus DNA-β satellite localizes sequences involved in replication

“…Because begomo-viruses can systemically infect N. benthamiana in the absence of DNA-b (Fig. 1a-d) and non-functional satellites can be maintained in plants (Cui et al, 2004;Saunders et al, 2004;Saeed et al, 2005), the inability to detect a satellite in systemically infected tissues suggests trans-replication incompatibility rather than a defect in satellite systemic movement mediated by the helper virus. With the exception of CLCuMV, which could maintain a low level of EpYVV DNA-b replication that was not detected in systemically infected tissues (Fig.…”