Towards identification of molecular mechanism in which the overexpression of wheat cytosolic and plastid glutamine synthetases in tobacco enhanced drought tolerance.

Glutamine synthetases (GS) play an essential role in Nitrogen assimilation. Nonetheless, information respecting the molecular functions of GS in drought tolerance (DT) is limited. Here we show that overexpressing cytosolic GS1 or plastidic GS2 gene in tobacco enhanced DT of both root and leaf tissues of the two transgenic seedlings (named as GS1-TR and GS2-TR). RNA-seq analysis on root tissues showed that 83 aquaporin (AQP) genes were identified. Among them, 37 differential expression genes (DEGs) were found in the GS1-TR roots under normal condition, and all were down-regulated; no any DEGs in the GS2-TR roots were found. Contrastingly, under drought, 28 and 32 DEGs of AQP were up-regulated in GS1-TR and GS2-TR roots, respectively. GC-MS analysis on leaf tissues showed that glutamine (Gln) concentrations were negatively correlated AQP expressions in the all four conditions, which suggests that Gln, as a signal molecule, can negatively regulate many AQP expressions. Prestress accumulation of sucrose and proline (Pro) and chlorophyll, and had higher activities of ROS scavengers also contribute the plant DT in both of the two transgenic plants under drought. In addition, 5-aminolevulinic acid (ALA) was up-accumulated in GS2-TR leaves solely under normal condition, which leads to its net photosynthetic rate higher than that in GS1-TR leaves. Last but not the less, the PYL-PP2C-SnRK2 core ABA-signaling pathway was uniquely activated in GS1-TR independent of drought stress (DS). Therefore, our results suggest a possible model reflecting how overexpression of wheat TaGS1 and TaGS2 regulate plant responses to drought.

BCR-ABL1 transcript decline ratio combined BCR-ABL1IS as a precise predictor for imatinib response and outcome in the patients with chronic myeloid leukemia.

Purpose: The early BCR-ABL1 reduction had the prognostic impact of the chronic-phase chronic myeloid leukemia (CML-CP) patients. This study was to find a more precise early prognosis index at 3 months in the patients with newly diagnosed CML-CP, especially for the patients with BCR-ABL1IS >10%. Methods: We retrospectively analyzed the data of 79 newly diagnosed CML-CP patients from October 2013 to April 2017. All patients took imatinib regularly and continuously and monitored BCR-ABL1 transcript level at baseline and 3, 6, 9, 12, 18 months after starting imatinib treatment. Results: Among the 44(55.7%) patients with BCR/ABL1IS ≤10% at 3 months after imatinib treatment, 12(27.3%) cases did not achieve major molecular response (MMR) at 12 months, and 7(14.9%) patients with the halving time BCR-ABL1 transcript ≤40 days failed to achieve MMR at 12 months. However, approximately twenty-six percent of the patients with BCR-ABL1IS >10% still obtained MMR. Moreover, the patients with BCR-ABL1IS ≤10% and halving time ≤40 days had a significantly better MMR than that of the patients with the BCR-ABL1IS ≤10% and halving time >40 days (88.6% versus 11.1%, P <0.001). However, the patients with the BCR-ABL1IS >10% and halving time >40 days rarely achieved MMR at 12 months. Conclusion: These data indicated that the halving time of BCR-ABL1 transcript was also an important prognostic factor as that of the BCR-ABL1IS. Combined observations of these two prognosis indexes are more accurate predictor for the long-term molecular response, especially for the CML-CP patients with BCR-ABL1IS >10%, and which is helpful for TKI switching as early as possible to improve patients' survival and reduce drug costs.

Nitrogen Supply and Leaf Age Affect the Expression of TaGS1 or TaGS2 Driven by a Constitutive Promoter in Transgenic Tobacco.

Glutamine synthetase (GS) plays a key role in nitrogen metabolism. Here, two types of tobacco transformants, overexpressing Triticum aestivum GS1 (TaGS1) or GS2 (TaGS2), were analysed. Four independent transformed lines, GS1-TR1, GS1-TR2, GS2-TR1 and GS2-TR2, were used for the nitrogen treatment. Under nitrogen-sufficient conditions, the leaves of GS2-TR showed high accumulation of the TaGS2 transcript, while those of GS1-TR showed a low TaGS1 transcript levels. However, compared with nitrogen-sufficient conditions, the TaGS1 transcript level increased in the leaves under nitrogen starvation, but the TaGS2 transcript level decreased. In addition, the TaGS1 and TaGS2 transcript levels were highest in the middle leaves under nitrogen-sufficient and starvation conditions. These results show that nitrogen supply and leaf age regulate TaGS expression, even when they are driven by a super-promoter. Additionally, in regard to nitrogen metabolism level, the lower leaves of the GS1-TR exhibited lower NH4⁺ and higher amino acid contents, while the upper leaves exhibited higher amino acid, soluble protein and chlorophyll contents. The leaves of the GS2-TR exhibited lower NH4⁺ but higher amino acid, soluble protein and chlorophyll contents. Given the role that GS isoforms play in nitrogen metabolism, these data suggest that TaGS1 overexpression may improve nitrogen transport, and that TaGS2 overexpression may improve nitrogen assimilation under nitrogen stress.

[Expression characteristics of glutamine synthetase of wheat in Escherichia coli].

Glutamine synthetase is a key enzyme in plant nitrogen assimilation. To study the structure of wheat glutamine synthetase isoenzymes, GS1, GSr, GSe, GS2 and GS2p of wheat were cloned into pET-21a, and the expression condition was optimized. Although wheat glutamine synthetase isoenzymes had 70%-80% amino acid sequence homology, the isoforms expressed with different characteristics. Induced at 30 °C, the most expression level of GSr, GSe and GS2 was after 3 h, and of GS1 was at the 7 h whereas no GS2p was expressed, and the GS isoenzymes showed different expression level, with the order of GS1 (22%)>GSr (15%)>GS2 (12%)>GSe (5%). GSe expressed as soluble protein, and GS1 expressed mainly as soluble protein whereas GSr and GS2 expressed as insoluble proteins. Induced at 30 °C for 3 h, mRNA transcript levels of GS isoforms were different, with the order of GSr (7.59)>GS2 (1.84)>GS2p (1.66)>GSe (1.46)>GS1 (1.00). The levels of mRNA transcription were not consistent with the level of the protein translation. The analysis of mRNA secondary structure showed the free energy of translation initiation region of glutamine synthetase isoforms was different, with the order of GS1 (14.4)GSr (13%)>GS2 (10%)>GSe (7%), and different activities with GS1>GSe>GS2, and the activity of GSr was not detected. The gene sequence of glutamine synthetase isoenzymes determines the amount, status and activity of proteins expressed in prokaryotic cells.