Figure 1.
(A) Transmembrane topology prediction for AtMPT1, AtMPT2, and AtMPT3. Hydropathy values were analyzed by TMPred prediction (http://www.ch.embnet.org/software/TMPRED_form.html). (B) Three- dimensional structures were predicted using their pdb coordinates and the Swiss-Model program (http://swissmodel.expasy.org).
Figure 2.
Expression patterns of the AtMPTs.
(A) Tissue-specific RNA expression. Total RNA was isolated from roots (R), primary shoot (S), rosette leaf (RL), cauline leaf (CL), flower (F), and siliques (Si) of 28-day-old wild-type (Col-0) plants and young rosette leaf (YL) and senescent rosette leaf (SL) of 14-day-old wild-type plants. AtMPT transcript levels were analyzed by quantitative real-time RT-PCR using gene-specific PCR primers. The transcript levels were normalized to that of elongation factor 1-a (EF1-α). Values are means±SEM of three replicates. (B) Histochemical analysis of expression patterns of the AtMPTs. Glucuronidase (GUS) activities in transgenic A. thaliana carrying the AtMPT1, AtMPT2, or AtMPT3 promoter::GUS constructs were analyzed by staining with X-gluc. Images were shown of flowers, siliques, seeds (embryos) and A. thaliana seedlings at different developmental stages.
Figure 3.
The roles of AtMPT in salt stress response.
(A) qRT-PCR analysis of AtMPT transcripts in wild-type plants and transgenic plants overexpressing AtMPTs under control and salt stress conditions. Ten-day-old seedlings grown on 1/2 MS agar media were transferred onto filter paper soaked with water and 150 mM NaCl for 24 h. The transcript level in the wild-type sample for AtMPT1 under control conditions was set to 1, and the other levels were calculated relative to the corresponding value. Values are means±SEM of three replicates. (B) Photographs of wild-type and overexpression lines were taken 10 days after germination on 1/2 MS agar media and 1/2 MS agar media with 150 mM NaCl. (C) Mean fresh weights (FW) of 10-day-old plants. (D) Mean radius of rosettes of 10-day-old plants. The overexpression lines for AtMPT3 under salt stress were damaged and had no normal rosette leaves to measure. Error bars represent±SEM. (E) Mean primary root lengths of 10-day-old plants. Error bars represent±SEM. Measurements shown in Figure C–E were made 10 days post-germination under control and high salinity stress conditions (n = 30). Samples with different letters are significantly different: P<0.01. OEMPTs, the AtMPT overexpressors.
Figure 4.
AtMPT mediates salt stress tolerance through an ATP-dependent pathway.
(A) ATP content in 10-day-old wild-type plants and the overexpression lines under control and 150 mM NaCl conditions. Values represent the average of three replicates±SEM. (B) Energy charge of 10-day-old wild-type plants and overexpression lines under control and salt stress. Values represent the average of three replicates±SEM. (C) Wild type and overexpressing seedlings germinated and grown under control and 150 mM NaCl together with 10 µM atractyloside. The pictures were taken 10 days post-germination. Samples with different letters are significantly different: P<0.05 (a and b, b and c). OEMPTs, the AtMPT overexpressors.
Figure 5.
Expression levels of the genes involved in gibberellin metabolism.
Expression levels of GA20ox, GA3ox, and GA2ox genes in wild-type and the AtMPT3 overexpression lines under control and salt stress. The mRNA levels of these genes were normalized against transcript levels of EF1-α. The transcripts of GA20ox5, GA3ox3 and GA2ox5 were not detected. Transcript level in the wild-type sample for each gene under control conditions was set to 1, and the other levels were calculated relative to the corresponding value. Values are means of three replicates with±SEM. OEMPTs, the AtMPT overexpressors.
Figure 6.
The role of gibberellin in AtMPT-modulated early responses to salt stress.
(A) ELISA-detectable gibberellin (GA1 and GA4) content of 10-day-old wild type and overexpression lines grown under control and high salinity stress. Values represent the average of three replicates±SEM. Samples with different letters are significantly different: P<0.01 (a and c, b and c) or P<0.05 (a and b). (B) Germination and seedling establishment was observed on control and 150 mM NaCl supplemented with 10 nM uniconazole. The pictures were taken 10 days post-germination. OEMPTs, the AtMPT overexpressors.