The role of tyrosyl-DNA phosphodiesterase 2 (Tdp2) involved in the repair of 5'-end-blocking DNA lesions is still poorly explored in plants. To gain novel insights， suspension cultures overexpressing the gene (Tdp2α-13C and Tdp2α-28 lines， respectively) and a control (CTRL) line carrying the empty vector were investigated. Transmission electron microscopy (TEM) revealed enlarged nucleoli (up to 44% expansion of the area， compared to CTRL)， the presence of nucleolar vacuoles， increased frequency of multinucleolate cells (up to 4.3-fold compared to CTRL) and reduced number of ring-shaped nucleoli in Tdp2α-13C and Tdp2α-28 lines. Ultrastructural data suggesting for enhanced nucleolar activity in -o... More
The role of tyrosyl-DNA phosphodiesterase 2 (Tdp2) involved in the repair of 5'-end-blocking DNA lesions is still poorly explored in plants. To gain novel insights， suspension cultures overexpressing the gene (Tdp2α-13C and Tdp2α-28 lines， respectively) and a control (CTRL) line carrying the empty vector were investigated. Transmission electron microscopy (TEM) revealed enlarged nucleoli (up to 44% expansion of the area， compared to CTRL)， the presence of nucleolar vacuoles， increased frequency of multinucleolate cells (up to 4.3-fold compared to CTRL) and reduced number of ring-shaped nucleoli in Tdp2α-13C and Tdp2α-28 lines. Ultrastructural data suggesting for enhanced nucleolar activity in -overexpressing lines were integrated with results from bromouridine incorporation. The latter revealed an increase of labeled transcripts in both Tdp2α-13C and Tdp2α-28 cells， within the nucleolus and in the extra-nucleolar region. -overexpressing cells showed tolerance to etoposide， a selective inhibitor of DNA topoisomerase II， as evidenced by DNA diffusion assay. TEM analysis revealed etoposide-induced rearrangements within the nucleolus， resembling the nucleolar caps observed in animal cells under transcription impairment. Based on these findings it is evident that -overexpression enhances nucleolar activity in plant cells.
