Understanding the Role of Durum Wheat Thioredoxin h-Type TdTrxh2 in Biotic Stress Tolerance

The thioredoxin h-type (Trxh) proteins play a crucial role as convergence points within plants’ responses to abiotic and biotic stresses. Previously, we demonstrated that the protein TdTrxh2 of durum wheat (Triticum durum Desf.) has a chaperone function and it promotes tolerance to abiotic stress. The aim of this study was to evaluate the antimicrobial effect of TdTrxh2 and its role in the response of durum wheat to Fusarium graminearum attack. First, we demonstrated the involvement of TdTrxh2 in the response of durum wheat to this fungus via the analysis of its expression profile under this fungus attack. In fact, the outcomes showed that the induction of TdTrxh2 expression is spatiotemporal in leaves and roots of durum wheat under F. graminearum infection. Interestingly, this induction was accompanied by H2O2 accumulation under short- and long-term stress in roots and leaves, respectively. Besides, the cis elements related to the two phytohormones ET and MeJA, and those implicated in defense and wound stress, were identified in the TdTrxh2 promoter’s sequence. Second, the purified TdTrxh2 protein possessed antimicrobial effects against a diverse range of bacteria and fungi in vitro. Finally, the expression of TdTrxh2 in transgenic Arabidopsis plants enhanced their tolerance to F. graminearum attack through the activation of the two H2O2-scavenging enzymes, CAT and POD, and via the induction of a subset of SA- and ABA-related genes. Moreover, the exogenous SA and ABA applications improved the growth of the transgenic lines compared to the non-transformed plants. Taken together, the results highlighted that TdTrxh2 generates tolerance of durum wheat’s response to F. graminearum attack, via the regulation of H2O2 homeostasis and the induction of hormone-associated genes. Thus, the TdTrxh2 gene could be considered as an interesting candidate gene to improve wheat tolerance to F. graminearum attack.