The tyrosyl-DNA phosphodiesterase gene family in Medicago truncatula Gaertn.: bioinformatic investigation and expression profiles in response to copper- and PEG-mediated stress

Abstract

The Tdp1 gene encoding tyrosyl-DNA phosphodiesterase has been extensively investigated in animal cells, due to the role of this enzyme in the repair of topoisomerase I-DNA covalent lesions. In contrast, information in this regard is totally missing in plants. We report for the first time in plants on the Tdp1 gene family from barrel medic (Medicago truncatula Gaertn.), composed of two members, hereby named MtTdp1alpha and MtTdp1beta. The expression profiles of MtTdp1alpha and MtTdp1beta genes were evaluated in plantlets grown in vitro using copper and polyethylene glycol (PEG 6000) as stress agents. In situ detection of reactive oxygen species (ROS) was carried out by histochemical staining, while the level of oxidative DNA damage, quantified in terms of 7,8-dihydro-8-oxoguanine (8-oxo-dG), increased up to 7.4- and 6.7-fold in response to copper and PEG 6000 treatments, respectively. Quantitative real-time polymerase chain reaction revealed that both Tdp1 genes were significantly up-regulated in response to copper and PEG. The Tdp1 genes were also significantly up-regulated during seed rehydration, an aspect of seed physiology in which DNA repair is a key component. Thus, the Tdp1 genes might be used as novel tools for improving stress tolerance in crops. The expression patterns of the barrel medic top1alpha and top1beta genes, encoding distinct isoforms of DNA topoisomerase I, were also analyzed and discussed to acquire additional information on their specific functions, closely related to that of the Tdp1 gene in animal cells.

Neuroprotection and repair of 3′-blocking DNA ends by glaikit (gkt) encoding Drosophila tyrosyl-DNA phosphodiesterase 1 (TDP1)

“…We show that Drosophila TDP1 hydrolyzes tyrosyl-DNA covalent bonds, just as previously reported for TDP1 in other species (2,11,16,25,43), which is consistent with the high conservation of TDP1 active site residues across species (Fig. S1).…”

DNA repair and telomere maintenance during seed imbibition: correlation of transcriptional patterns

“…The Tdp1α gene was up-regulated during early imbibition (Fig. 1), in agreement with the expression profiles described in M. truncatula by Macovei et al [13] . Similarly, the Tdp2α gene was activated at 1-6 h. To date, the only link between the Tdp2 function and telomere length in plants has been provided by Confalonieri et al [20] .…”

“…For each tested gene, the transcript level both in dry seeds and in cotyledons/root tip is shown at different time points during rehydration. The time period (0-12 h) corresponding to the activation of DNA repair genes, essential step for preserving seed vigour [13,14,15,16] is highlighted. Expression of TERT gene, encoding Arabidopsis telomerase reverse transcriptase, was observed in both cotyledons and radicle with a peak of TERT mRNA levels occurring during the 18-30 h time frame.…”

The TFIIS and TFIIS-like genes from Medicago truncatula are involved in oxidative stress response

“…The copper concentration estimated by EPR in M. truncatula leaves is in agreement with data previously obtained by spectrometric analyses (Macovei et al, 2010), as well as the good resolved lines of the copper nucleus hyperfine coupling, and is indicative of the fact that most of the copper ions are in one predominant single species in the Cu 2+ redox state. However, we cannot exclude the possibility that Cu + ions underwent oxidation to Cu 2+ .…”