Compensatory expression and substrate inducibility of gamma-glutamyl transferase GGT2 isoform in Arabidopsis thaliana.
γ-Glutamyl transferases (GGT; EC 2.3.2.2) are glutathione-degrading enzymes that are represented in Arabidopsis thaliana by a small gene family of four members. Two isoforms, GGT1 and GGT2, are apoplastic, sharing broad similarities in their amino acid sequences, but they are differently expressed in the tissues: GGT1 is expressed in roots, leaves, and siliques, while GGT2 was thought to be expressed only in siliques. It is demonstrated here that GGT2 is also expressed in wild-type roots, albeit in very small amounts. GGT2 expression is enhanced in ggt1 knockout mutants, suggesting a compensatory effect to restore GGT activity in the root apoplast. Supplementation with 100  μM glutathione (GSH) resulted in the up-regulation of GGT2 gene expression in wild-type and ggt1 knockout roots, and of GGT1 gene expression in wild-type roots. Glutathione recovery was hampered by the GGT inhibitor serine/borate, suggesting a major role for apoplastic GGTs in this process. These findings can explain the ability of ggt1 knockout mutants to retrieve exogenously added glutathione from the growth medium.
Department of Agricultural Biotechnology, University of Padua, Viale Università 16, 35020 Legnaro (PD), Italy.
Tiziana
T
Destro
Dinesh
D
Prasad
Damiano
D
Martignago
Ignacio Lliso
IL
Bernet
Anna Rita
AR
Trentin
Indu Kumari
IK
Renu
Massimo
M
Ferretti
Antonio
A
Masi
D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005978:Glutathione / Q000378:metabolism*; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D005723:gamma-Glutamyltransferase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D005723:gamma-Glutamyltransferase; D005978:Glutathione