Post-Translational Modification of Formate Dehydrogenase, a Stress-Response Protein
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The ability of a plant to adapt to environmental stress is crucial for its ability to grow, develop to maturity and produce yield. The ubiquitination pathway is a post-translational mechanism that aids plants in producing a coping response to stressful conditions such as cold, drought, and pathogen infection. Central to the ubiquitination pathway are the ubiquitin ligases (E3s) that select and mediate attachment of ubiquitin molecules to substrate proteins. A common outcome for tagged proteins is destruction to by the 26S proteasome. The targets of an E3 ligase include proteins involved in many aspects of plant growth, development, hormone signaling, pathogen resistance and tolerance of abiotic stresses. Keep on Going (KEG) is an E3 ligase that negatively regulates the actions of the hormone abscisic acid (ABA) during early seedling establishment. A search for other targets of KEG identified formate dehydrogenase (FDH), which has been previously characterized as a stress response protein. FDH converts formate into carbon dioxide, serving to alleviate any detrimental effects accumulated formate has on the cell. It was of interest to this study to determine if FDH is ubiquitinated and degraded by the 26S proteasome and if KEG is responsible for the regulation of FDH abundance. Results show that FDH is ubiquitinated and phosphorylated in planta and that KEG has the capability to attach ubiquitin molecules to FDH in vivo. It has also been shown that FDH is being degraded by the 26S proteasome. In addition, Arabidopsis thaliana seedlings overexpressing KEG were more sensitive to exogenous formate than their wild-type counter parts. These results suggest that FDH is regulated by KEG, indicating yet another possible role for KEG in modulating plants ability to respond to and cope with environmental stress.