| The phytohormone abscisic acid (ABA), which regulates many agronomically important aspects of plant life, including seed development and dormancy, plays a critical role in plant stress responses such as drought, salinity and cold shock . These physiological responses to ABA are in large part due to changes in gene expression and a complex signal transduction network . Several transcription factors mediating ABA responses have been isolated.A variety of second messengers contribute to the transmission of the ABA signal. Down stream signalling involves a complex network of both positive and negative regulators. As a common topic in signal transduction, protein phosphorylation also seems to play an important role in ABA signaling. Biochemical and molecular genetic studies in Arabidopsis have identified PP2C enzymes as key players in plant signal transduction processes.Genetic evidence has implicated Arabidopsis PP2Cs (ABI1,ABI2,HAB1,HAG3 and PP2CA) as negative regulators of the ABA signal pathway. Whereas ABI1 is central regulators of ABA signalling both in seeds and vegetative tissues.Thellungiella halophila ,a close-relative of Arabidopsis thaliana, which is been suggested and be developed as a new salt tolerance model plant. Studying the function and mechanism of the ThABI1 can help to further reveal the mechanism of ABA singling pathway in Thellungiella halophila , and it give a understabding of the mechanisms of plant stress-tolerance.The research includes the following contents:1. The full cDNA sequence of ThABI1 in Thellungiella halophila was cloned;2. The results showed that the expression of ThABI1 is been up-regulated under drought, salt, cold, ABA in Thellungiella halophila by Real-time quantitative PCR;3. Over-expression Study of ThABI1 in Thellungiella halophila wild type:The plant over-expression vector of 35S promoter∷ThABI1 in pCAMBIA3301 was constructed. The vector of 35S∷ThABI1 has transferred into Agrobacterium tumefaciens GV3101, and was introduced into Thellungiella halophila (wt) by dipping method. The transformed plants of 35S∷ThABI1 were screened by using 0.2% Basta, and gained Basta-resistance plants, The Basta-resistance plants were further identified: Bar gene(500bp) were showed strong positive signals by PCR, and no signal was shown in Thellungiella halophila (wt). It was showed that 35S∷ThABI1 gene was been in the genome of Thellungiella halophila.4. Gene silence study of ThABI1 in Thellungiella halophila: ThABI1∷pCAMBIA3301 is silencing vector and it was introduced into Thellungiella halophila (wt) by dipping method. The transformed plants of ThABI1∷pCAMBIA3301 were screened by using 0.2%Basta, and gained Basat-resistance plants. The Basta-resistant plants were further identified as follows: (1) Bar gene(500bp) were showed strong positive signals by PCR, and no signal was shown in Thellungiella halophila (wt); (2) Comparing the expression level between transgenic lines and wide type by real-time quantitative PCR, we found expression level of ThABI1 have been decreased by different levels in transgenic plants.(3) The expression of ThABI1 were up-regulated under the 60μmol/L ABA for 0, 3, 6 hours in the transgenic lines by real-time quantitative PCR.5. The analysis of AtHKT1 promoter∷ThHKT1 in Arabidopsis HKT1 mutant(sas2-1) are as follows: (1) The Na+ contents of AtHKT1 promoter∷ThHKT1 transgenic lines are similar with that of sas2-1 in shoot, but higher than that of the wild type under the different concentration of NaCl (0,75,125mmol/L); (2) The K+ content of AtHKT1 promoter∷ThHKT1 transgenic lines are much higher than that of sas2-1 in shoot under the different K+ concentrations (0,50,100 mmol/L). Our results suggested that ThHKT1 improve the content of the K+ in all transgenic plants under the condition of normal and high-K+, and also reduced the transportation of Na+ into the shoot. In all it is indicates that HKT1 in Thellungiella halophila as function of K+ transporter,and it can regulated Na+ and K+ ion homeostasis.
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