Functional validation of Lobularia maritima thioredoxin-h2 protein for its ability to combat bacterial and fungal infections

Thioredoxins (Trxs) belong to a family of multifunctional redox proteins that is critical for maintaining and regulating the cellular redox environment during plant cell growth. Also, they are important for the development of plant’s response to biotic and abiotic stress; however, the specific biological functions of h-type thioredoxins (Trxhs) in plants have not been fully elucidated. Herein, we investigated the role of LmTrxh2, a specific member of the Trxh family, in response to various biotic stress simulants, including mechanical wounding, exposure to jasmonic acid (JA), picolinic acid (PA), salicylic acid (SA), ethephon (ETP), and hydrogen peroxide (H2O2). We observed that LmTrxh2 transcripts were significantly upregulated upon exposure to these stress simulants. The characterization of enzymatic activity revealed that the recombinant LmTrxh2 protein functions as a disulfide reductase. While the role of Trx proteins in redox regulation is well known, their involvement in antimicrobial activity is still unexplored. Therefore, we assessed the antimicrobial effect of LmTrxh2 towards various microorganisms and observed a concentration-dependent inhibition of microbial growth. The minimum inhibitory and minimum bactericidal concentrations and the diameters of the inhibition zones were 40–1250 μg/mL, 40–1250 μg/mL, and 12.5–32.5 mm, respectively. In addition, we used previously developed LmTrxh2-transgenic tobacco lines and found that they showed enhanced resistance to fungal infections triggered by Fusarium graminearum and Aspergillus niger. This resistance was associated with an upregulation of known defense-related genes. Overall, our findings suggest that LmTrxh2 is responsive to multiple biotic stress simulants and plays a critical role in the basal resistance of plants to pathogen infections. These results highlight the potential of LmTrxh2 in the development of strategies to protect crops from various stress factors and emphasize its importance in the adaptation of plants to different stress conditions.