A Novel Thaumatin-Like Protein from Durum Wheat, TdPR-5, is Homologous to Known Plant Allergens, Responsive to Stress Exposure, and Confers Multiple-Abiotic Stress Tolerances to Transgenic Yeast

Thaumatin-like proteins (TLPs) are highly complex group of Pathogenesis-Related proteins (PRs) recognized as human allergens. They are known to rapidly accumulate in high levels following stresses. Several members of TLPs were isolated from different plant species, but few were described in durum wheat. In this study, a PR-5 member, TdPR-5, was isolated from a Tunisian variety of durum wheat. Phylogenetic analysis showed that TdPR-5 protein shared high homology with TLPs isolated from several plant species. Allergenic assessment of TdPR-5, using Allermatch tool, revealed that TdPR-5 had significant identity with TLPs, known as plant allergens. qRT-PCR analysis revealed that TdPR-5 is robustly induced by drought, salt and heavy metals such as cadmium (Cd), copper (Cu) and zinc (Zn). Notably, TdPR-5 induction is concomitant with the induction of the durum wheat transcription factor TdSHN1 shown previously to control the expression of tobacco PR-5 gene when overexpressed in transgenic tobacco plants. Maximum fold-change in relative expression of TdPR-5 and TdSHN1 genes following stress treatments reached 6.5 times (mannitol 1 h) and 10 times (Cu 24 h), respectively. Heterologous expression of TdPR-5 in transgenic yeast conferred resistance to multiple abiotic stresses. These results indicated that TdPR-5 may play an important role in multiple abiotic stress tolerance in wheat. This study also provides valuable information regarding food safety. In fact, overexpression of strong transcription factors such as TdSHN1 or exposure of plants to stressful conditions can lead to an increase in the quantity of allergens in crops thereby increasing the risk for consumers with known allergy or sensitization.