Redox response of iron-sulfur glutaredoxin GRXS17 activates its holdase activity to protect plants from heat stress

Abstract

Living organisms use a large panel of mechanisms to protect themselves from environmental stress.Particularly, heat stress induces misfolding and aggregation of proteins which are guarded by chaperone systems. Here, we examine the function the glutaredoxin GRXS17, a member of thiol reductases families in the model plant Arabidopsis thaliana. GRXS17 is a nucleocytosolic 30 monothiol glutaredoxin consisting of an N-terminal thioredoxin (TRX)-domain and three CGFSactive site motif-containing GRX-domains that coordinate three iron-sulfur (Fe-S) clusters in a glutathione (GSH)-dependent manner. As a Fe-S cluster-charged holoenzyme, GRXS17 is likely involved in the maturation of cytosolic and nuclear Fe-S proteins. In addition to its role in cluster biogenesis, we showed that GRXS17 presents both foldase and redox-dependent holdase activities. 35Oxidative stress in combination with heat stress induces loss of its Fe-S clusters followed by subsequent formation of disulfide bonds between conserved active site cysteines in the corresponding TRX domains. This oxidation leads to a shift of GRXS17 to a high-MW complex and thus, activates its holdase activity. Moreover, we demonstrate that GRXS17 is specifically involved in plant tolerance to moderate high temperature and protects root meristematic cells from 40 heat-induced cell death. Finally, we showed that upon heat stress, GRXS17 changes its client proteins, possibly to protect them from heat injuries. Therefore, we propose that the iron-sulfur cluster enzyme glutaredoxin GRXS17 is an essential guard to protect proteins against moderate heat stress, likely through a redox-dependent chaperone activity. All in all, we reveal the mechanism of an Fe-S cluster-dependent activity shift, turning the holoenzyme GRXS17 into a holdase that 45 prevents damage caused by heat stress.

Glutathione-mediated plant response to high-temperature

“…Next, we studied the response of the glutathione deficient mutants to the same high temperature regimes. A 37°C heat regime mimicking a heat wave is commonly called Thermotolerance to Moderate High Temperature (TMHT) (Yeh et al, 2012) (Martins et al, 2020b). Here, seeds are germinated at standard temperature for 4 days before to be transferred to 37°C for 5 further days.…”