| Low temperature, drought, and high salinity are common stress conditions that adversely affect plant growth and crop productivity. It is well known that in China there are lots of droughty and semiarid land, accounting for 38% of the arable land, and great acres of saline soil need increasing productivity and reclamation. In addition, low/freezing temperatures restrict the planting and harvest of crops in a year-round manner. Therefore, enhancing the plant ability against environmental stresses is critical for increasing the yield of crops.Oxidative stress is the common mechanism by which abiotic stresses affect plant growth and development. Under adverse environmental conditions, such as drought, high salinity and low temperature, the endogenous level of plant hormone ABA (Absicisic Acid) rapidly increases which leads to excess production of reactive oxygen species (ROS), resulting in the formation of oxidative stress that causes irreversible injuries to plants. To scavenge excess ROS and reduce its toxic effects, plants have evolved an antioxidant system whose activity is up-regulated under stressful conditions and correlated well with enhanced tolerance. However, due to the poor capability for induction of the various enzymes of the antioxidant defense system, the degree of the enhancement is limited. Therefore, a more enhanced anti-oxidant ability is required for improving plant stress tolerance.As a part of the anti-oxidant system of Maize, Call gene plays an indispensable role in scavenging excess cellular H2O2. Our previous studies have demonstrated that the expression of Catl is ABA-inducible which is mediated by ABRE2 motif in its promoter and transcription factor ABP9 that specifically interacts with ABRE2 motif of Maize Catl gene has been cloned. Given that ABRE motif is located in the promoters of many stress-induced genes, it will be interesting to know if ABP9 can trigger the expression of a battery of stress-related genes and contributes to the improvement of plant performance under abiotic stresses. My research focuses on addressing these questions by analyzing the role of ABP9 expression in Maize suspension cells and in transgenic Arabidopsis plants.The research work and the main conclusions are as follows:1. Two ABP9 constructs were made, pAHC25ABP9 and pBI121ABP9, for transient expression in Maize suspension cells and stable transformation of Arabidopsis, respectively.2. Transcription activation expression vector (pAHC25ABP9) and reporter vector (pIGA) were co-transformed into Maize suspension cells by biolistic method. The GUS staining results indicated that ABP9 was able to bind to ABRE motif and activate the expression of downstream reporter gene (GUS). Thus we conclude that ABP9 protein functions as a transcription activator regulating gene expression through specifically binding to ABRE motif.3. ABP9 transgenic Arabidopsis plants were obtained through agro-bacterium -mediated transformation via vacuum infiltration. Identification of transgenic plants by PCR was done on 62 kanamycin resistant TI plants and revealed that 75.8% of them were PCR positive.4. Five of homozygous ABP9 transgenic lines were used to analyze the expression of ABP9 and other stress-related genes by Northern blotting. The results showed that ABP9 gene was over-expressed and its expression level in the five lines was different, with 5 line the strongest. The expression of stress-related genes, cor47, cor 15a, kinl and erd!4, was either activated or enhanced comparing to their expression in the wild-type control.5. Stress tolerance assays of ABP9 transgenic Arabidopsis plants showed that ABP9 significantly improved plant performance under stress conditions, such as high salt, freezing and drought.6. ESR method was employed to quantify the level of reactive oxygen species in plants. The results showed that the expression of ABP9 gene in Arabidopsis led to about 50% decrease of ROS amount in transgenic plants, compared with that hi non-transgenic ones. The results...
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