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.
Destro
Tiziana
T
Department of Agricultural Biotechnology, University of Padua, Viale Università 16, 35020 Legnaro (PD), Italy.
Prasad
Dinesh
D
Martignago
Damiano
D
Bernet
Ignacio Lliso
IL
Trentin
Anna Rita
AR
Renu
Indu Kumari
IK
Ferretti
Massimo
M
Masi
Antonio
A
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