The FRO2 ferric reductase is required for glycine betaine's effect on chilling tolerance in Arabidopsis roots.
FRO2 (At1g01580) codes for an NADPH-dependent ferric reductase in plasma membranes of root epidermal cells with a demonstrated role in iron uptake by plants. Ferric reductase activity has been shown to be the rate-limiting step for iron uptake in strategy I plants like Arabidopsis and in rice, but it has been unclear whether FRO genes have other physiological functions. We hypothesized that FRO2 was involved in chilling stress tolerance because its expression was upregulated by treatment of plants with glycine betaine (GB), a chemical that prevents reactive oxygen species (ROS) signaling in chilling stress. This idea was confirmed by showing that the FRO2 null mutant frd1-1 failed to respond to GB in chilling assays either in relation to root growth recovery or inhibition of ROS accumulation. Measurements of ferric reductase activity in wild-type plants treated with GB before chilling showed no significant GB effect compared with controls. In addition, 35S-FRO2 transgenics with elevated mRNA levels did not have improved chilling tolerance. However, ferric reductase activity in wild-type plants or 35S-FRO2 transgenics pretreated with GB was several-fold higher after chilling compared with non-pretreated controls. These experiments identify a new physiological function for FRO2, i.e. blocking ROS accumulation during chilling. They also suggest that GB has a major effect on FRO2 activity posttranscriptionally in the cold.
Einset
John
J
Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, 1432 Aas, Norway. john.einset@umb.no
Winge
Per
P
Bones
Atle M
AM
Connolly
Erin L
EL
D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001622:Betaine / Q000494:pharmacology*; D003080:Cold Temperature; D038181:FMN Reductase / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D009154:Mutation; D018517:Plant Roots / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D029681:Arabidopsis Proteins; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D001622:Betaine; D038181:FMN Reductase; C023903:ferric citrate iron reductase