Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is involved in DNA repair pathways as it mends the topoisomerase I—DNA covalent complexes. In plants, a small
Tdp1 gene family, composed by
Tdp1α and
Tdp1β genes, was identified, but the roles of these genes in abiotic stress responses
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Tyrosyl-DNA phosphodiesterase 1 (Tdp1) is involved in DNA repair pathways as it mends the topoisomerase I—DNA covalent complexes. In plants, a small
Tdp1 gene family, composed by
Tdp1α and
Tdp1β genes, was identified, but the roles of these genes in abiotic stress responses are not fully understood. To investigate their specific stress response patterns, the present study made use of bioinformatic and molecular tools to look into the
Tdp1β gene function, so far described only in the plant kingdom, and compare it with
Tdp1α gene coding for the canonical, highly conserved α isoform. The expression profiles of
Tdp1α and
Tdp1β genes were examined under abiotic stress conditions (cold, heat, high osmolarity, salt, and UV-B) in two model species,
Arabidopsis thaliana and
Medicago truncatula. The two isoforms of topoisomerase I (
TOP1α and
TOP1β) were also taken into consideration in view of their known roles in DNA metabolism and cell proliferation. Data relative to gene expression in
Arabidopsis were retrieved from the AtGenExpress microarray dataset, while quantitative Real-Time PCR was carried out to evaluate the stress response in
M. truncatula cell cultures. These analyses revealed that
Tdp1β gene expression was enhanced during the first hour of treatment, whereas
Tdp1α enhanced expression succeeded at subsequent timepoints. In agreement with the gene-specific responses to abiotic stress conditions, the promoter regions of
Tdp1α and
Tdp1β genes are well equipped with stress-related
cis-elements. An in-depth bioinformatic characterization of the HIRAN motif, a distinctive feature of the
Tdp1β protein, showed its wide distribution in chromatin remodeling and DNA repair proteins. The reported data suggests that
Tdp1β functions in the early response to abiotic stresses.
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