Degradation mechanisms of the Tomato yellow leaf curl virus coat protein following inoculation of tomato plants by the whitefly Bemisia tabaci.
BACKGROUND
Tomato yellow leaf curl virus (TYLCV) is a begomovirus infecting tomato cultures worldwide. TYLCV is transmitted to plants by the whitefly Bemisia tabaci. Once in the plant, the virus is subjected to attack by the host-plant defences, which may include sequestration in aggregates, proteolysis, ubiquitination, 26S proteasome degradation and autophagy. Elucidating how the virus avoids destruction will make it possible to understand infection and possibly devise countermeasures.


RESULTS
The accumulation of viral coat protein (CP) and of viral DNA in plants is a marker of a successful virus transmission by B. tabaci. In response to infection, tomato tissues display multiple ways of degrading TYLCV proteins and DNA. In this study it is shown that CP (in soluble and insoluble states) is the target of protease digestion, 26S proteasome degradation and autophagy. The highest degradation capacity was detected among soluble proteins and proteins in large aggregates/inclusion bodies; cytoplasmic extracts displayed higher activity than nuclear fractions. The very same fractions possessed the highest capacity to degrade viral genomic DNA. Separately, 26S proteasome degradation was associated with large aggregates (more pronounced in the nuclear than in the cytoplasmic fractions), which are indicators of a successful abduction of plants by viruses. Autophagy/lysosome/vacuole degradation was a characteristic of intermediate aggregates, sequestering the CP in the cytoplasm and retarding the development of large aggregates. Chloroplast proteases were active in soluble as well as in insoluble protein extracts.


CONCLUSIONS
To the best of the authors' knowledge, this study is the first attempt to identify elements of the virus-targeted degradation machinery, which is a part of the plant response to virus invasion.
Institute of Plant Sciences and Genetics in Agriculture and the Otto Warburg Minerva Centre for Agricultural Biotechnology, Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.
Rena
R
Gorovits
Adi
A
Moshe
Murad
M
Ghanim
Henryk
H
Czosnek
D000818:Animals; D001343:Autophagy; D053839:Begomovirus / Q000276:immunology* / Q000378:metabolism*; D036022:Capsid Proteins / Q000378:metabolism; D004279:DNA, Viral / Q000378:metabolism*; D006430:Hemiptera / Q000821:virology; D007303:Insect Vectors / Q000821:virology; D018551:Solanum lycopersicum / Q000276:immunology* / Q000821:virology*; D010447:Peptide Hydrolases / Q000378:metabolism; D010935:Plant Diseases / Q000276:immunology* / Q000821:virology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism
D036022:Capsid Proteins; D004279:DNA, Viral; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex
immune response; protease and nuclease; protein quality control; whitefly-mediated inoculation