Overexpression of the Glutathione Peroxidase 5 (RcGPX5) Gene From Rhodiola crenulata Increases Drought Tolerance in Salvia miltiorrhiza

Abstract

Excessive cellular accumulation of reactive oxygen species (ROS) due to environmental stresses can critically disrupt plant development and negatively affect productivity. Plant glutathione peroxidases (GPXs) play an important role in ROS scavenging by catalyzing the reduction of H₂O₂ and other organic hydroperoxides to protect plant cells from oxidative stress damage. <i>RcGPX5</i>, a member of the GPX gene family, was isolated from a traditional medicinal plant <i>Rhodiola crenulata</i> and constitutively expressed in <i>Salvia miltiorrhiza</i> under control of the CaMV 35S promoter. Transgenic plants showed increased tolerance to oxidative stress caused by application of H₂O₂ and drought, and had reduced production of malondialdehyde (MDA) compared with the wild type. Under drought stress, seedlings of the transgenic lines wilted later than the wild type and recovered growth 1 day after re-watering. In addition, the reduced glutathione (GSH) and total glutathione (T-GSH) contents were higher in the transgenic lines, with increased enzyme activities including glutathione reductase (GR), ascorbate peroxidase (APX), and GPX. These changes prevent H₂O₂ and O₂ ^- accumulation in cells of the transgenic lines compared with wild type. Overexpression of <i>RcGPX5</i> alters the relative expression levels of multiple endogenous genes in <i>S. miltiorrhiza</i>, including transcription factor genes and genes in the ROS and ABA pathways. In particular, <i>RcGPX5</i> expression increases the mass of <i>S. miltiorrhiza</i> roots while reducing the concentration of the active ingredients. These results show that heterologous expression of <i>RcGPX5</i> in <i>S. miltiorrhiza</i> can affect the regulation of multiple biochemical pathways to confer tolerance to drought stress, and <i>RcGPX5</i> might act as a competitor with secondary metabolites in the <i>S. miltiorrhiza</i> response to environmental stimuli.