Identification of the methionine sulfoxide reductase (MSR) gene family in four Triticum species and functional analysis of TaMSRB5 involved in copper stress tolerance in Arabidopsis thaliana.

Methine sulfoxide reductase (MSR) plays a crucial role in protecting plants from oxidative damages. However, their involvement in copper (Cu) detoxification remains largely uncharacterized. In this study, we identified 17 MSR genes in wheat (Triticum aestivum), 12 MSR genes in Triticum dicoccoides (Td), 6 in Triticum urartu (Tu), and 5 in Aegilops tauschii (Aet). Strong collinearity and conservation were found among orthologs. Three constitutively expressed homoeologs of TaMSRB5 were significantly upregulated in leaves and downregulated in roots of wheat seedlings when exposed to excessive Cu. Overexpression of TaMSRB5 in Arabidopsis significantly enhanced Cu tolerance as evidenced by increased fresh weight and root length in transgenic plants, compared to wild-type (WT, Col-0). Under Cu toxicity, Arabidopsis overexpression lines accumulated similar levels of Cu in their leaves and roots compared with WT. However, they exhibited elevated levels of oxidized glutathione (GSSG), total glutathione (T-GSH), along with Glutathione S-transferase (GST), superoxide dismutase (SOD) and catalase (CAT) activities. Simultaneously, they showed reduced levels of reactive oxygen species (ROS) and malondialdehyde (MDA), and a lower GSH/ GSSG ratio, indicating enhanced ROS scavenging ability. Consistent with the moderation of oxidative stress, comparative transcriptome analysis revealed that four GST genes were upregulated in transgenic Arabidopsis plants under Cu stress, suggesting the potential relationship between these genes with TaMSRB5 in Cu detoxification. The findings demonstrate the pivotal role of TaMSRB5 in enhancing Cu tolerance in Arabidopsis and provide novel insights into the molecular mechanisms underlying Cu detoxification.