Involvement of Arabidopsis glutaredoxin S14 in the maintenance of chlorophyll content

Plant class-II glutaredoxins (GRXs) are oxidoreductases carrying a CGFS active site signature and are able to bind iron-sulfur clusters invitro. In order to explore the physiological functions of the 2 plastidial class-II isoforms, GRXS14 and GRXS16, we generated knockdown and overexpression Arabidopsis thaliana lines and characterized their phenotypes using physiological and biochemical approaches. Plants deficient in one GRX did not display any growth defect, whereas the growth of plants lacking both was slowed. Plants overexpressing GRXS14 exhibited reduced chlorophyll content in control, high-light, and high-salt conditions. However, when exposed to prolonged darkness, plants lacking GRXS14 showed accelerated chlorophyll loss compared to wild-type and overexpression lines. We observed that the GRXS14 abundance and the proportion of reduced form were modified in wild type upon darkness and high salt. The dark treatment also resulted in decreased abundance of proteins involved in the maturation of iron-sulfur proteins. We propose that the phenotype of GRXS14-modified lines results from its participation in the control of chlorophyll content in relation with light and osmotic conditions, possibly through a dual action in regulating the redox status of biosynthetic enzymes and contributing to the biogenesis of iron-sulfur clusters, which are essential cofactors in chlorophyll metabolism. In this work, we aimed at characterizing the physiological functions of the plastidial class-II glutaredoxins (GRXs), GRXS14 and GRXS16, two oxidoreductases able to bind iron-sulfur clusters in vitro. We observed that plants deficient in a single GRX do not display any growth defect, whereas the growth of plants lacking both was slowed. Plants overexpressing GRXS14 exhibited reduced chlorophyll content, whereas plants lacking GRXS14 showed accelerated chlorophyll loss upon prolonged darkness, a condition resulting in GRXS14 oxidation and in strong decreases in the abundance of proteins involved in the maturation of iron-sulfur proteins. Hence, GRXS14 would participate in chlorophyll maintenance by regulating the redox status of biosynthetic enzymes and/or the biogenesis of iron-sulfur proteins involved in chlorophyll metabolism.