The FRO2 ferric reductase is required for glycine betaine’s effect on chilling tolerance in Arabidopsis roots

Abstract

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.

Glycinebetaine mediates chromium tolerance in mung bean through lowering of Cr uptake and improved antioxidant system

“…Moreover, the reduction was higher under severe Cr (500 µM) stress as compared to lower Cr Similarly, Einset et al (2008) reported that GB might activate the expression of genes of ROS scavenging enzymes which protects the photosynthetic machinery from damage under stressful conditions. In present study, increase in plant growth and biomass might be due to decreased Cr concentration in plants ( Figure 5) and enhanced the activities of antioxidant enzymes (Figure 4).…”

Improved salt tolerance and seed cotton yield in cotton (Gossypium hirsutum L.) by transformation with betA gene for glycinebetaine synthesis

“…Because both foliar-applied GB and genetically generated GB in the cytosol are transported into chloroplasts, even if only to a small extent (Chen and Murata 2011;Park et al 2006). In addition, GB, either applied exogenously or synthesized in vivo in transgenic plants, can also activate specific genes which wholly or partly regulated a reduction in the stress-induced accumulation of ROS (Allard et al 1998;Einset and Connolly 2009;Einset et al 2007Einset et al , 2008Kathuria et al 2009;Park et al 2006).…”

Glycinebetaine protects plants against abiotic stress: mechanisms and biotechnological applications

“…Einset et al . (2007, 2008) demonstrated, in Arabidopsis , that exogenous application of 100 m m GB to both leaves and roots improved tolerance of roots to chilling stress via regulation of the expression of a number of stress‐tolerance genes.…”

“…In the case of the FRO2 gene for ferric reductase, the FRO‐null mutant, frd1‐ 1, failed to respond to GB in chilling assays in terms both of recovery of root growth and of inhibition of the accumulation of ROS (Einset et al . 2008).…”

“…These results suggest that (1) FRO2 blocks the accumulation of ROS during chilling and, thus, enhances chilling tolerance; and (2) GB has a major post‐transcriptional effect on the activity of FRO2 in the cold. Overall, at least three proteins, namely, RabA4c GTPase (At5g47960), bZIP transcription factor (At3g62420) and FRO2 ferric reductase (At1g01580), are required for GB‐induced chilling tolerance (Einset et al . 2007, 2008).…”