Glycine betaine enhances extracellular processes blocking ROS signaling during stress.

It has now been demonstrated that treatment of plants with glycine betaine (GB) improves tolerance to chilling stress by regulating gene expression. This finding provides the opportunity to identify new stress determinants using gene expression profiling with microarrays followed by functional confirmation of the involvement of candidate genes via mutant studies. The first gene identified by this approach was the gene for RabA4c GTPase (At5g47960), which is expressed in roots and is involved in vesicle trafficking from the Golgi Apparatus to the plasma membrane. Recently, we have identified the FRO2 ferric reductase (At1g01580) which is localized on the plasma membrane, as another component of the GB-regulated system and suggested that enhanced production of reductant in the cell wall also plays a role in chilling tolerance. This addendum article focuses on the concept that extracellular processes may play a pivotal role in stress tolerance. A candidate gene list is presented for GB-upregulated genes in Arabidopsis roots and a model is proposed incorporating candidate genes with potential roles in relation to reactive oxygen species (ROS) signaling and chilling stress.