Department of Agricultural Biotechnology, University of Padua, Viale Università 16, 35020 Legnaro (PD), Italy.
J Exp Bot. 2011 Jan;62(2):805-14. doi: 10.1093/jxb/erq316. Epub 2010 Oct 19.
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.
γ-谷氨酰转移酶（GGT；EC 2.3.2.2）是一种谷胱甘肽降解酶，在拟南芥中由一个包含四个成员的小基因家族代表。两种同工酶，GGT1 和 GGT2，是质外体的，它们在氨基酸序列上有广泛的相似性，但在组织中的表达不同：GGT1 在根、叶和蒴果中表达，而 GGT2 被认为仅在蒴果中表达。本文证明 GGT2 也在野生型根中表达，尽管量非常少。在 ggt1 敲除突变体中，GGT2 的表达增强，表明存在一种补偿效应，以恢复根质外体中的 GGT 活性。用 100 μM 谷胱甘肽（GSH）进行补充，导致野生型和 ggt1 敲除根中的 GGT2 基因表达上调，以及野生型根中的 GGT1 基因表达上调。GGT 抑制剂丝氨酸/硼酸阻碍了谷胱甘肽的恢复，表明质外体 GGT 在这个过程中起主要作用。这些发现可以解释 ggt1 敲除突变体从生长培养基中回收外源添加的谷胱甘肽的能力。
