Virus induced gene silencing of three putative prolyl 4-hydroxylases enhances plant growth in tomato (Solanum lycopersicum)
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Proline hydroxylation is a major posttranslational modification of hydroxyproline-rich glycoproteins (HRGPs) that is catalyzed by prolyl 4-hydroxylases (P4Hs). HRGPs such as arabinogalactan proteins (AGPs) and extensios play significant roles on cell wall structure and function and their implication in cell division and expansion has been reported. We used tobacco rattle virus (TRV)-based virus induced gene silencing to investigate the role of three tomato P4Hs, out of ten present in the tomato genome, in growth and development. Eight-days old tomato seedlings were infected with the appropriate TRV vectors and plants were allowed to grow under standard conditions for 6 weeks. Lower P4H mRNA levels were associated with lower hydroxyproline content in root and shoot tissues indicating successful gene silencing. P4H-silenced plants had longer roots and shoots and larger leaves. The increased leaf area can be attributed to increased cell division as indicated by the higher leaf epidermal cell number in SlP4H1- and SlP4H9-silenced plants. In contrast, SlP4H7-silenced plants had larger leaves due to enhanced cell expansion. Western blot analysis revealed that silencing of SlP4H7 and SlP4H9 was associated with reduced levels of JIM8-bound AGP and JIM11-bound extensin epitopes, while silencing of SlP4H1 reduced only the levels of AGP proteins. Collectively these results show that P4Hs have significant and distinct roles in cell division and expansion of tomato leaves.
KeywordsArabinogalactan proteins Extensins Prolyl 4-hydroxylase Solanum lycopersicum Tobacco rattle virus Virus induced gene silencing
We would like to thank Prof. Dr. Constantinos Fasseas (Electron Microscopy Laboratory, Agricultural University of Athens, Greece), Prof. Dr. Polydefkis Hatzopoulos and Dr. Christos Michaelides (Department of Agricultural Biotechnology, Agricultural University of Athens, Greece) for their help in Scanning Electron Microscopy analysis, Dr. Panagiotis Kefalas (Mediterranean Agronomic Institute of Chania, Greece) for synthesizing β-Yariv reagent and Prof. Dr. Paul J. Knox (Centre for Plant Sciences, University of Leeds, UK) for providing the extensin and AGP monoclonal antibodies. This work benefited from the networking activities within the European funded COST ACTION FA1106 “Qualityfruit”.
Conflict of interest
The authors declare that they have no conflict of interest.
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