Dear Editor,Glutaredoxins (Grxs) are glutathione-dependent thiol disulfide oxidoreductases of the thioredoxin family present in all organisms from bacteria to human (Noguera et al.,2005).Depending on their active site sequence,Grxs are essentially classified into three families:the dithiol Grxs,the monothiol Grxs and the CC type restricted to plants (Rouhier et al.,2008).Grxs play important biological functions in plants,such as oxidative stress responses,iron-sulfur (FeS)cluster assembly,and cell signaling,etc.(Rouhier et al.,2008).There are totally 31 Grxs isoforms in Arabidopsis thaliana,and 19 Grx isoforms in Populus trichocarpa (Rouhier et al.,2004),For Grxs of Populus trichocarpa,structures of GrxC1,GrxC4 and GrxS12 have been resolved,all belong to dithiol Grxs (Noguera et al.,2005;Feng et al.,2006;Rouhier et al.,2007;Couturier et al.,2009).The only structure available for monothiol Grxs in plants is that of Arabidopsis Grxcp,which is also called GrxS14 or CAXIP1 (Cheng and Hirschi,2003;Li et al.,2010).