Genome-Wide Identification, Characterization, and Expression Analysis Revealed the Involvement of Brachypodium H-Type Thioredoxin Gene Family in Abiotic Stress Response

Thioredoxins (Trxs) are thiol-disulfide oxidoreductase proteins that play an important role in plant development and abiotic stress tolerance through redox regulation of target proteins. In plants, the individual biological functions of H-type thioredoxins (Trxhs) are still poorly known. This work is the first to identify the Trxh gene family of the trio of Brachypodium genus (B. distachyon, B. stacei, and B. hybridium) and to characterize their evolutionary patterns and expression profiles under abiotic stress. In total, 28 Trxh proteins were identified in the trio of Brachypodium species that can be divided into three groups. Interestingly, a new unusual Trxh protein (Trxh7) harboring two Cysteine (Cys) residues in its N-terminal region was discovered. Gene structure and protein-conserved motif analyses further consolidated the classification of the phylogenetic tree and highlighted the functional divergence of the Trxh family. Tandem and whole-genome duplications were found as major forces driving Trxh gene expansion in Brachypodium species. The duplicated Trxh gene pairs underwent a purifying selection during the evolution. In silico expression analysis showed the differential expression of BdTrxhs during development. Moreover, based on RT-qPCR expression analysis, target BdTrxh members were found to be induced by salt and drought stresses concomitantly with an accumulation of hydrogen peroxide (H2O2) in root tissues. The exogenous application of H2O2 modulated almost the same BdTrxh genes in root and leaf tissues. These results suggest specific roles for Trxh genes in B. distachyon beside their potential implication in abiotic stress response via redox homoeostasis.