Giaretta Sabrina, Prasad Dinesh, Forieri Ilaria, Vamerali Teofilo, Trentin Anna Rita, Wirtz Markus, Hell Rüdiger, Masi Antonio
Department of Agronomy, Food, Natural Resources, Animals and the Environment (DAFNAE), University of Padova, Viale dell'Università 16, Legnaro 35020, Padova, Italy.
Department of Bio-Engineering, Birla Institute of Technology, Mesra, Ranchi, Jharkhand 835215, India.
Plant Physiol Biochem. 2017 Jun;115:44-56. doi: 10.1016/j.plaphy.2017.03.007. Epub 2017 Mar 10.
Gamma-glutamyl transferase (GGT; EC 2.3.2.2) is the only enzyme capable of degrading glutathione (GSH) in extra-cytosolic spaces. In plant cells, the GGT1 and GGT2 isoforms are located in the apoplast, bound respectively to the cell wall and the plasma membrane. GGT1 is expressed throughout plants, mainly in the leaves and vascular system, while GGT2 is more specifically expressed in seeds and trichomes, and weakly in roots. Their role in plant physiology remains to be clarified, however. Obtaining the ggt1/ggt2 double mutant can offer more clues than the corresponding single mutants, and to prevent any compensatory expression between the two isoforms. In this work, ggt1/ggt2 RNAi (RNA interference) lines were generated and characterized in the tissues where both isoforms are expressed. The seed yield was lower in the ggt1/ggt2 RNAi plants due to the siliques being fewer in number and shorter in length, with no changes in thiols and sulfur compounds. Proline accumulation and delayed seed germination were seen in one line. There were also fewer trichomes (which contain high levels of GSH) in the RNAi lines than in the wild type, and the root elongation rate was slower. In conclusion, apoplastic GGT silencing induces a decrease in the number of organs with a high GSH demand (seeds and trichomes) as a result of resource reallocation to preserve integrity and composition.
γ-谷氨酰转移酶（GGT；EC 2.3.2.2）是唯一能够在胞外空间降解谷胱甘肽（GSH）的酶。在植物细胞中，GGT1和GGT2同工型位于质外体，分别与细胞壁和质膜结合。GGT1在整个植物中都有表达，主要在叶片和维管系统中，而GGT2更特异性地在种子和毛状体中表达，在根中表达较弱。然而，它们在植物生理学中的作用仍有待阐明。获得ggt1/ggt2双突变体比相应的单突变体可以提供更多线索，并且可以防止两种同工型之间的任何补偿性表达。在这项工作中，在两种同工型都表达的组织中产生并表征了ggt1/ggt2 RNA干扰（RNAi）株系。由于角果数量减少和长度变短，ggt1/ggt2 RNAi植株的种子产量较低，硫醇和硫化合物没有变化。在一个株系中观察到脯氨酸积累和种子萌发延迟。RNAi株系中的毛状体（其中含有高水平的GSH）也比野生型少，并且根伸长率较慢。总之，质外体GGT沉默由于资源重新分配以保持完整性和组成，导致对GSH需求高的器官（种子和毛状体）数量减少。
