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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 MtTdp1α and MtTdp1β. The expression profiles of MtTdp1α and MtTdp1β 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 top1α and top1β 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. [ABSTRACT FROM AUTHOR]

Oligonucleotide microarrays corresponding to over 16,000 genes were used to analyze changes in transcript accumulation in root tips of the Al-sensitive Medicago truncatula cultivar Jemalong genotype A17 in response to Al treatment. Out of 2,782 genes with significant changes in transcript accumulation, 324 genes were up-regulated and 267 genes were down-regulated at least twofold by Al. Up-regulated genes were enriched in transcripts involved in cell-wall modification and abiotic and biotic stress responses while down-regulated genes were enriched in transcripts involved in primary metabolism, secondary metabolism, protein synthesis and processing, and the cell cycle. Known markers of Al-induced gene expression including genes associated with oxidative stress and cell wall stiffening were differentially regulated in this study. Transcript profiling identified novel genes associated with processes involved in Al toxicity including cell wall modification, cell cycle arrest and ethylene production. Novel genes potentially associated with Al resistance and tolerance in M. truncatula including organic acid transporters, cell wall loosening enzymes, Ca2+ homeostasis maintaining genes, and Al-binding were also identified. In addition, expression analysis of nine genes in the mature regions of the root revealed that Al-induced gene expression in these regions may play a role in Al tolerance. Finally, interfering RNA-induced silencing of two Al-induced genes, pectin acetylesterase and annexin, in A17 hairy roots slightly increased the sensitivity of A17 to Al suggesting that these genes may play a role in Al resistance. [ABSTRACT FROM AUTHOR]