Chloroplasts lacking class I glutaredoxins are functional but show a delayed recovery of protein cysteinyl redox state after oxidative challenge

Genome-wide identification and expression analysis of glutaredoxin in Puccinellia tenuiflora under salinity stress

BACKGROUND

Glutaredoxins (GRX) are key oxidoreductases that modulate protein redox states during plant development and stress responses. Alkaligrass (Puccinellia tenuiflora) is a highly salt-tolerant forage grass, but its GRX gene family (PutGRXs) remains uncharacterized, unlike those in Arabidopsis and other plants.

RESULTS

We identified 25 PutGRX genes in the P. tenuiflora genome. Phylogenetic analysis revealed close evolutionary ties to monocotyledonous rice (Oryza sativa). Based on gene structure and conserved domains, PutGRXs were classified into three groups: five CGFS-type, eleven CPYC-type, and nine CC-type GRXs. Promoter analysis identified numerous cis-acting elements linked to abiotic stresses (e.g., light, drought, heat, cold) and hormone responses, suggesting a pivotal role in stress adaptation. Tissue-specific expression profiling showed differential PutGRX expression in roots, leaves, stems, flowers, and sheaths, with most genes responding to NaCl, NaHCO3, and Na2CO3 stresses. Functional characterization of chloroplast-localized PutGrxS12 demonstrated its importance in plant growth and ROS scavenging under salinity stress.

CONCLUSION

This study offers the first comprehensive genomic and functional analysis of the PutGRX family in P. tenuiflora, highlighting its conservation, classification, and stress-responsive roles. Our findings advance understanding of GRX-mediated stress tolerance and provide potential targets for engineering salt-resistant crops.

Chloroplast thiol redox dynamics through the lens of genetically encoded biosensors

Chloroplasts fix carbon by using light energy and have evolved a complex redox network that supports plastid functions by (i) protecting against reactive oxygen species and (ii) metabolic regulation in response to environmental conditions. In thioredoxin- and glutathione/glutaredoxin-dependent redox cascades, protein cysteinyl redox steady states are set by varying oxidation and reduction rates. The specificity and interplay of these different redox-active proteins are still under investigation, for example to understand how plants cope with adverse environmental conditions by acclimation. Genetically encoded biosensors with distinct specificity can be targeted to subcellular compartments such as the chloroplast stroma, enabling in vivo real-time measurements of physiological parameters at different scales. These data have provided unique insights into dynamic behaviours of physiological parameters and redox-responsive proteins at several levels of the known redox cascades. This review summarizes current applications of different biosensor types as well as the dynamics of distinct protein cysteinyl redox steady states, with an emphasis on light responses.

Localization of four class I glutaredoxins in the cytosol and the secretory pathway and characterization of their biochemical diversification

Class I glutaredoxins (GRXs) are catalytically active oxidoreductases and considered key proteins mediating reversible glutathionylation and deglutathionylation of protein thiols during development and stress responses. To narrow in on putative target proteins, it is mandatory to know the subcellular localization of the respective GRXs and to understand their catalytic activities and putative redundancy between isoforms in the same compartment. We show that in Arabidopsis thaliana, GRXC1 and GRXC2 are cytosolic proteins with GRXC1 being attached to membranes through myristoylation. GRXC3 and GRXC4 are identified as type II membrane proteins along the early secretory pathway with their enzymatic function on the luminal side. Unexpectedly, neither single nor double mutants lacking both GRXs isoforms in the cytosol or the ER show phenotypes that differ from wild-type controls. Analysis of electrostatic surface potentials and clustering of GRXs based on their electrostatic interaction with roGFP2 mirrors the phylogenetic classification of class I GRXs, which clearly separates the cytosolic GRXC1 and GRXC2 from the luminal GRXC3 and GRXC4. Comparison of all four studied GRXs for their oxidoreductase function highlights biochemical diversification with GRXC3 and GRXC4 being better catalysts than GRXC1 and GRXC2 for the reduction of bis(2-hydroxyethyl) disulfide. With oxidized roGFP2 as an alternative substrate, GRXC1 and GRXC2 catalyze the reduction faster than GRXC3 and GRXC4, which suggests that catalytic efficiency of GRXs in reductive reactions depends on the respective substrate. Vice versa, GRXC3 and GRXC4 are faster than GRXC1 and GRXC2 in catalyzing the oxidation of pre-reduced roGFP2 in the reverse reaction.