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Characterization and transient replication of tomato leaf curl virus defective DNAs
S A A Behjatnia1, I B Dry, M A Rezaian
1CSIRO Plant Industry, Glen Osmond, Australia.
Archives of Virology
|March 10, 2007
Summary
Defective DNA molecules in tomato leaf curl virus (TLCV) infections lack essential viral genes but retain replication origins. These molecules replicate with TLCV but cannot spread within whole plants, indicating replication dependence on the virus.
Area of Science:
- Plant Virology
- Molecular Biology
- Genetics
Background:
- Tomato leaf curl virus (TLCV) infection in plants can generate distinct subgenomic DNA species known as defective (df) DNA molecules.
- These df DNAs possess large deletions, compromising viral replication, encapsidation, and spread.
- Crucially, the viral origin of replication (ori) and replication-associated protein (Rep) binding domains are retained in these df DNAs.
Purpose of the Study:
- To investigate the replication and movement capabilities of TLCV-derived defective DNA molecules.
- To identify the minimal sequence requirements for df DNA replication mediated by TLCV.
- To understand the role of viral components in the lifecycle of defective DNA.
Main Methods:
- Isolation and characterization of four distinct df DNA species from TLCV-infected plants.
- Co-agroinfection of plant leaf strips and whole plants with viral DNA and df DNA constructs.
- Mutational analysis of df DNA sequences to determine replication requirements.
- Association studies with TLCV coat protein to assess encapsidation.
Main Results:
- All four characterized df DNAs contained the viral origin of replication (ori) with Rep binding domains, despite deletions in other viral genes.
- Co-agroinfection enabled df DNA replication in leaf strips when supplied with the respective TLCV strain.
- However, df DNAs failed to exhibit systemic movement in whole plants even when co-inoculated with TLCV, suggesting a dependence on the virus for spread.
- DF DNA molecules were found associated with TLCV coat protein, indicating potential encapsidation.
Conclusions:
- Defective DNA molecules generated during TLCV infection are replication-dependent on the helper virus.
- The intergenic region containing Rep-binding domains is the minimum requirement for df DNA replication by TLCV.
- While df DNAs can be replicated and potentially encapsidated, they are unable to spread systemically within the plant independently.
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