Abstract
Topoisomerases are unique enzymes having an ability to remove or add DNA supercoils and untangle the snarled DNA. They can cut, shuffle, and religate DNA strands and remove the torsional stress during DNA replication, transcription or recombination events. In the present study, we over-expressed topoisomerase II (TopoII) in tobacco (Nicotiana tabaccum) and examined its role in growth and development as well as salt (NaCl) stress tolerance. Several putative transgenic plants were generated and the transgene integration and expression was confirmed by PCR and Southern blot analyses, and RT-PCR analysis respectively. Percent seed germination, shoot growth, and chlorophyll content revealed that transgenic lines over-expressing the NtTopoIIα-1 gene exhibited enhanced tolerance to salt (150 and 200 mM NaCl) stress. Moreover, over-expression of TopoII lead to the elevation in proline and glycine betaine levels in response to both concentrations of NaCl as compared to wild-type. In response to NaCl stress, TopoII over-expressing lines showed reduced lipid peroxidation derived malondialdehyde (MDA) generation. These results suggest that TopoII plays a pivotal role in salt stress tolerance in plants.
Highlights
Unwinding of the DNA double helix is either transient as in transcription and recombination or stable as during DNA replication (Champoux, 2001)
DNA topoisomerase was first isolated from Escherichia coli by James Wang in 1971 and was named as ω protein known as DNA topoisomerase I (TopoI; Wang, 1971)
We proposed that TopoII under GAL1 promoter functionally complements a temperature-sensitive topoisomerase IIts yeast mutant (Singh et al, 2003) and its transcript levels get up-regulated in response to cold and salinity stress in tobacco and pea (Hettiarachchi et al, 2005)
Summary
Unwinding of the DNA double helix is either transient as in transcription and recombination or stable as during DNA replication (Champoux, 2001). DNA being negatively supercoiled, the strand separation by helicases first relaxes DNA but further duplex melting leads to positively supercoiled strands that impede the action of helicases (Capranico et al, 2010). Topoisomerases ubiquitously present in both prokaryotes and eukaryotes play a crucial role in untangling and relaxing the interwound DNA supercoiled duplex, thereby mitigating the topological stress (Vos et al, 2011; Ashour et al, 2015). DNA topoisomerase was first isolated from Escherichia coli by James Wang in 1971 and was named as ω protein known as DNA topoisomerase I (TopoI; Wang, 1971). Type I topoisomerases are ATP independent-monomeric proteins which nick and seal only one strand of DNA changing the linking number of supercoiled DNA by steps of one, whereas the type II topoisomerases are
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