| Drought stress is one of the most important factors affecting plant growth, development, survival and crop productivity. An important way for the improvement of crop tolerance to drought is to identify and functionally characterize drought-related genes. Drought-related mutants in model plant Arabidopsis are widely used to elucidate the mechanism of drought tolerance in plant. When plants are subjected to water deficit, plant cells perceive the drought signal to trigger a cellular signal transduction pathway enabling them to survive. Drought stress can affect the interaction between the plasma membrane and cell wall of plant cells. The cell wall and/or cell wall-plasma membrane interaction is essential in sensing drought stress. Accumulating evidence has shown that there is a cell wall-plasma membrane-cytoskeleton continuum in plant cells, which plays important roles in the regulation of plant responses to drought stress.AT14A mediates the cell wall-plasma membrane-cytoskeleton continuum. AT14A may be a substantial middle member of the cell wall-plasma membrane-cytoskeleton continuum and play an important role in the continuum by regulating cell wall and cortical cytoskeleton organization. The sequence and structural similarity of AT14A to the integrins of animals suggests that AT14A may be an integrin-like protein in Arabidopsis. In this study, we try to gain further insight into the function of AT14A, especially clarify the functions and molecular mechanisms of AT14A protein in the processes of signal transduction under drought stress. The suspension cultured cells and plants of Arabidopsis mutants (at14a), transgenic overexpressing AT14A (AT14A-OE) and wild type were used. PEG-6000 treatment was used as drought stress. Various approaches and techniques, including analysis of gene expression, plant physiology and biochemistry, transcriptome and quantitative proteomics analysis, bioinformatics, etc. were also applied.The main results are as follows:1.The expression of AT14A was induced by PEG-6000 resulting from reverse transcription-PCR in the suspension cultured cells. Compared to the wild-type cells, overexpression of AT14A (AT14A-OE) in Arabidopsis cultures exhibited a greater ability to adapt to water deficit, as evidenced by higher biomass accumulation and cell survival rate. Furthermore, AT14A-OE cells showed a higher tolerance to PEG-induced oxidative damage, as reflected by less H2O2 content, lipid peroxidation (malondialdehyde (MDA) content), and ion leakage, which was further verified by maintaining high levels of activities of antioxidant defense enzymes such as scorbate peroxidase and guaiacol peroxidase and soluble protein. Taken together, the results suggest that AT14A plays an important regulatory role in response to drought stress in Arabidopsis suspension cells. Overexpression of AT14A improves drought stress tolerance and AT14A is involved in inhibition of oxidative damage in part through enhancing antioxidant enzyme activities to suppress the levels of ROS as well as lipid peroxidation and electrolyte leakage in suspension cultures of Arabidopsis.2. AT14A was more highly expressed in leaves than in roots, flowers and stems. The RT-PCR results showed that the AT14A expression in leaves was induced by PEG-6000. Compared to the WT plant under soil drought, the mutant at14a plant was more sensitive to drought stress. The different genes expression in both genotypic was analysed after drought stress by a transcriptomic approach. There were 681 up-regulated difference genes and 613 down-regulated different genes in WT plant compared with the control under drought stress, while there were 1018 up-regulated different genes and 1413 down-regulated different genes in mutant at 14a plant. Q-PCR results showed that the expression of ABA biosynthesis-related genes (AAO3,NCED5) and ABA-dependent drought stress-related genes (RAB18,RD22) was significantly accumulated in both genotypes under drought stress. However, a lower expression of the molecules (AAO3,NCED5,RAB18,RD22) was found in mutant at14a plant when compared to WT plant upon exposure to drought stress. ABA content was significantly accumulated in both genotypes under drought stress. There was a significant tendency for a lower ABA accumulation in mutant at14a plant when compared to WT plant upon exposure to drought stress types like PEG treatment. The results show that AT14A plays an important role in drought stress-induced ABA synthesis by regulating ABA biosynthesis-related genes (AAO3,NCED5) to response to drought stress in Arabidopsis. Besides, AT14A is involved in response to drought stress through regulating ABA-dependent drought stress-related genes (RAB18,RD22)3. The different proteins expression in both genotypic was analysed after drought stress by a proteomics approach. There were totally 123 difference proteins in WT and at 14a plant including 71 up-regulated proteins and 52 down-regulated proteins. There were totally 625 difference proteins in WT and atl4a plant under drought stress including 339 up-regulated proteins and 286 down-regulated proteins. Under drought stress, the expression of antioxidant defense enzyme APX1 and V-H+ATPase E1 in two genotypes plant was increased, but lower expression of APX1 and V-H+ATPase El was found in mutant (at 14a) plant compared to the wild-type (WT) plant. The results further demonstrate that AT14A is involved in inhibition of oxidative damage. AT14A is also involved in response to drought stress possibly through regulating V-H+ATPase El.In conclusion, AT14A plays an important role in response to drought stress in Arabidopsis. These results not only help us to laid a foundation for further study of the molecular biological function of AT14A but also provide a foundation and guidance for improving plant drought tolerance through molecular techniques both theoretically and practically.
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