Thioredoxins as hormone-responsive redox regulators in wheat: transcriptomic and structural insights

Thioredoxins (TRXs) are small central redox proteins involved in stress responses and plant development, but their hormone-dependent regulation remains poorly characterized. In this study, a genome-wide identification of the TRX family in Triticum aestivum (Ta) was performed using Arabidopsis thaliana TRXs as orthologs. Phylogenetic analysis allowed the identification of a total of 48 TRXs, including 22 typical TRXs, 22 atypical TRXs, and four thioredoxin reductases (TRs). The identified classes in wheat were conserved compared with the Arabidopsis genome; however, no extra classes were identified. To assess the regulation of the wheat TRX genes under hormonal treatments, including abscisic acid (ABA), ethylene (ET), indole-3-acetic acid (IAA), and methyl jasmonate (MeJA), an in silico analysis was performed using the GEO dataset. The transcriptomic analysis and the quantitative reverse transcription PCR (qRT-PCR) validation revealed that the atypical TRXs were more responsive to hormones than the typical TRXs and TRs. Among these atypical TRX members, atypical cysteine/histidine rich thioredoxin (ACHT), chloroplast drought stress protein of 32 kDa (CDSP32), nucleoredoxin (NRX), and TRX-L3 groups were the most hormone-responsive. ABA strongly upregulated the TaACHT4.2 gene, whereas TaNRX1.1 responded to IAA and ET. On the other hand, ABA, IAA, ET, and MeJA downregulated TaCDSP32.1, TaNRX1.2, TaNRX1.3, and ACHT members. The molecular docking analysis suggested a potential interaction between the selected atypical TRXs and ABA, IAA, and MeJA. The multidomain TRXs, such as TaCDSP32.1 and TaNRX1.1, showed a high affinity for ABA and IAA, whereas TaTRX-L3.1.3 showed a high affinity for MeJA. This study highlights the importance and potential functions of poorly characterized atypical TRXs as hormone-responsive redox regulatory nodes in wheat and provides a basis for future functional validation under hormonal and stress conditions, as well as during plant development.