Glutathione S-transferases modulate Cu tolerance in Oryza sativa

Abstract

Along with the widespread use of copper (Cu)-based fungicides and fertilizers, Cu-contaminated soil has been a major issue resulting in the loss of crop yield. To improve Cu tolerance in Oryza sativa, we previously carried out a screen of Cu sensitivity and obtained the Cu tolerant (B1139) and the Cu sensitive (B1195) rice varieties. Here, by analyzing an RNA-Seq transcriptome profile of root tips, 20 glutathione S-transferase (GST) genes were differently expressed between the Cu tolerant B1139 and the Cu sensitive B1195 when exposed to excess Cu2+. A more rapid decrease of root GST activity occurred in Cu-treated B1195 than in Cu-treated B1139, suggesting that different GST activity might affect Cu tolerance in rice. This is further supported by the observation of Cu hypersensitivity in rice seedlings deficient of the most abundant GST protein, OsGSTF2, demonstrating that GST proteins modulate Cu tolerance in rice. This, at least partially, leads to different Cu tolerance between B1139 and B1195. Furthermore, homologous modeling showed that a putative Cu2+ binding site, OsGSTF2H41 locates at the active center of GST enzyme. In vitro analysis demonstrated that Cu2+ interferes with the GST activity of OsGSTF2 protein, indicating that GST activity reduction by Cu2+ might be the binding of Cu2+ to the OsGSTF2H41 site. Consistently, amino acid replacement of histidine 41 with glycine (OsGSTF2H41G) resulted in decreased GST activity of OsGSTF2. Additionally, ectopic expression of OsGSTF2 enhances Cu tolerance in Escherichia coli, suggesting that the GST proteins might alleviate Cu toxicity by the binding of free Cu2+ in cells.