The Relationship Between The BR Regulated-protein PMRP And Stress-tolerance In Arabidopsis

In nature, plants often encounter great changes of environmental conditions. And if the change extent is above the normal life scope of the plants, the plants will be damaged or die. As a result, improving plants’ resistance has a great effect on increasing the productivity of the plants. So far, brassinosteroids are one kind of plant growth hormones which are internationally recognized as high efficient, broad-spectrum and non-toxic. It can not only improve the physiological metabolism but also enhance plants’ ability of stress-tolerance. Therefore, to make clear of the stress-tolerance mechanism of BRs has directive significance to its economical and effective application in agricultural production.The analysis of the function and action mechanism of the BR regulated-proteins involved in adversity regulation is the basis of improving plant resistance. PMRP(a putative membrane-related protein, At3g13062), a conjectural membrane protein regulated by BR, is likely to play an important role in regulating plant adversity. In this study, the function and mechanism of PMRP in the stress regulation were analyzed. The results were as follows:1. PMRP consists of 411 amino acids and it contains START domain. The START domain has the function of the involved in lipid transport and metabolism; PMRP contains phosphatidylcholine binding sites. Therefore, PMRP is likely to be involved in the stress regulation of plants.2. On the basis of the gain-function and loss-function transgenic Arabidopsis’ response to the drought stress, salt, and cold stress, we analyzed the role of PMRP in Arabidopsis adversity regulation.(1) PMRP played a role in the process of Arabidopsis’ tolerance to draught. After planning the wild type(Col-0) and PMRP transgenic Arabidopsis seeds on the one-half-strength Murashige(MS) culture medium supplemented with/without 300 m M mannitol and culturing for 10 d, the results showed that under the 300 m M mannitol treatment, the green leaves rate of wild type(Col-0) was 62.2%. However, the green leaves rate of the three lines of over expression PMRP transgenic Arabidopsis were 35.3%, 31.8%, 25.2% respectively and the green leaves rate of the three lines of PMRP-RNAi transgenic Arabidopsis lines were 62.8%, 60.7%, 61.4% respectively, which indicated that the increase of the PMRP expression quantity reduced Arabidopsis’ tolerance against drought resistance but the decrease of PMRP expression quantity had no obvious effect on Arabidopsis’ tolerance against drought resistance.(2) PMRP played a role in the process of Arabidopsis’ tolerance to salt. After planning the wild type(Col-0) and PMRP transgenic Arabidopsis seeds on the one-half-strength MS culture medium supplemented with/without 150 m M Na Cl and culturing for 10 d, the results showed that under 150 m M Na Cl treatment, the green leaves rate of wild type(Col-0) was 64.6%. However, the green leaves rate of the three lines of over expression PMRP transgenic Arabidopsis were 10.6%, 19.7%, 18.2% respectively and the green leaves rate of the three lines of PMRP-RNAi transgenic Arabidopsis were 56.8%, 63.7%, 57.6% respectively, which indicated that the increase of the PMRP expression quantity also reduced Arabidopsis’ tolerance against salt resistance and the decrease of PMRP expression quantity had no obvious effect on Arabidopsis’ tolerance against salt resistance.(3) PMRP played a role in the process of Arabidopsis’ tolerance to coldness. All the wild type(Col-0), over expression PMRP transgenic Arabidopsis and PMRP-RNAi transgenic Arabidopsis were grown at 21°C with a 16-h-light/8-h-dark cycle. After 21 d, they were transferred to 4°C cold light incubator for 7 d and then cultivate for 1.5 h at 8°C. After it they were take out again to the indoor cultivation at 21°C with a 16-h-light for 7 d, the green leaves rate of wild type(Col-0) was 48%. However, the green leaves rate of the three lines of over expression PMRP transgenic Arabidopsis were 48.6%, 47.8%, 49.2% respectively, and the green leaves rate of the three lines of PMRP-RNAi transgenic Arabidopsis were 65.9%, 67.4%, 68.3% respectively, which indicated that the decrease of PMRP expression quantity enhanced Arabidopsis’ tolerance to cold stress.3. The analysis of the function mechanism of PMRP which participate in the Arabidopsis’ adversity regulation. Under the adversity stress, cell membrane permeability and photosynthesis is the physiological index of plant stress response. Cold stress can affect the structure of chloroplast, so we determinated cell membrane permeability and photosynthetic rate of the PMRP gain-function and loss-function transgenic Arabidopsis lines and observed chloroplast ultrastructure of it.(1) PMRP effects on the stability of cell membrane. We selected the wild type(Col-0), over expression PMRP transgenic Arabidopsis and PMRP-RNAi transgenic Arabidopsis which growth in the 14 d and determined the exudates’ conductivity of rosette leaf. The results showed that under 150 m M Na Cl treatment for 4 h, wild type(Col-0) showed 78.77 μS.cm-1, while the three lines of over expression PMRP transgenic Arabidopsis were 84.47, 96.17, 85.0 μS.cm-1 respectively, which indicated that the increase of the PMRP expression quantity aggravated salt stress’ damage to the cell membrane. When exposure to-8°C for 30 min, the exudates conductivity of wild type(Col-0) showed 70.67 μS.cm-1, while the three lines of PMRP-RNAi transgenic Arabidopsis were 48.57, 45.40, 52.10 μS.cm-1 respectively, which indicated that the decrease of PMRP expression quantity greatly reduced adversity’s damage to the cell membrane.(2) PMRP effects on photosynthetic rate in Arabidopsis thaliana. We selected wild type(Col-0), over expression PMRP transgenic Arabidopsis and PMRP-RNAi transgenic Arabidopsis, all of which were grown at 21°C with a 16-h-light/8-h-dark cycle for 14 d, and then determined the photosynthetic rate of rosette leaf. The results showed that photosynthetic rate of wild type(Col-0) was 7.3 umol/m2.s while the PMRP-RNAi transgenic Arabidopsis were 8.8, 7.8 and 8.5 umol/m2·s respectively, which indicated that the decrease of PMRP expression quantity slightly enhanced the photosynthetic rate of Arabidopsis.(3) PMRP effects on ultrastructure of chloroplast and accumulation of starch grains. We selected fully expanded rosette leaf of wild type(Col-0) and PMRP-RNAi transgenic Arabidopsis, all of them were grown at 21°C with a 16-h-light/8-h-dark cycle, and then observe the ultrastructure of it. The results showed that chloroplast was oval in the cells of rosette leaf of wild type(Col-0), but chloroplast was approximate circle shape in PMRP-RNAi transgenic Arabidopsis. Under light, the accumulation of starch grains increased in the chloroplast of the PMRP transgenic Arabidopsis was similar to that of the wild type. But in the dark environment, the accumulation of starch granules in chloroplasts of PMRP-RNAi transgenic Arabidopsis increased significantly.