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

The cDNA sequence coding for a novel putative TFIIS (transcription elongation factor II-S), hereby named MtTFIIS-like, was isolated from barrel medic (Medicago truncatula Gaertn.) by reverse transcriptase-polymerase chain reaction. The nucleotide sequence contains an open reading frame of 1074 bp, predicting a 40.0 kDa protein, conserved among plant species. The N-terminal region of the MtTFIIS-like protein includes a LW motif, characterized by highly conserved leucine (L) and tryptophan (W) residues, also found in the canonical TFIIS protein, elongin A (transcription elongation factor S-III) and CRSP70 (cofactor required for Sp1 activation), while a proline-rich region is present in the C-terminal domain. The expression profiles of the MtTFIIS-like gene were evaluated by quantitative real-time PCR (QRT-PCR) in barrel medic plantlets grown in vitro under oxidative stress conditions induced by copper (CuCl2 0.05, 0.1 and 0.2 mM) and polyethylene glycol (PEG6000 50, 100 and 150 g/L), respectively. Both stress agents caused ROS (reactive oxygen species) accumulation. Moreover, EPR spectra of leaves from plantlets exposed to toxic copper doses confirmed that the heavy metal is translocated from roots to the aerial parts, where it is found predominantly in the Cu2+ redox state. The MtTFIIS-like gene expression was significantly enhanced (up to 2.9-fold) in aerial parts of copper-treated plants, and in roots (up to 4.4-fold) in response to PEG treatments. The expression profiles of the MtTFIIS-like gene were compared to those of the MtTFIIS gene, encoding the canonical TFIIS protein, which was similarly up-regulated in response to both stresses. Interestingly, the MtTFIIS-like and MtTFIIS genes were significantly up-regulated (up to 3.2- and 4.3-fold, respectively) during seed imbibition, a physiological process which requires active DNA repair. Based on the reported data, the possible roles played in planta by the novel MtTFIIS-like gene are discussed.