| The soil salification is a serious problem for resource and environment. On the one hand, the soil salification causes a great deal of pressure to the balance of the ecosystem, on the other hand, it reduces the area of the cultivated land seriously. There are 950 million hm2 saline-alkali soil in the world. And China has a total area of about 100 million hm2 saline soil, Halostachys caspica is a kind of succulent halophyte semishrub in desert. Their suitable value for salt-tolerant of its seed is 332.5 mmo1 / L, the critical value is 540.0 mmol / L, and the limit value is 749.0 mmo1 / L. So it is very significant to do research on Halostachys caspica as it has so high resistant to saline.Plant microRNAs are single-stranded RNA molecules with about 21 nucleotides (nt) in length that belong to noncoding RNA family. They act as post- transcriptional negative regulators of gene expression mainly by guiding cleavage or attenuating ranslation of target transcripts. Studies on Arabidopsis seed germination have shown that: miR417 were significantly reduced in the process of seed germination under salt stress.The study on plant microRNA is mainly focusd on their function on gene exepresion, growth and deveopment at present. Furthermore, the model plant and the economic crops were mainly used as micioRNA research materials. There is no report about the relation between microRNAs and halophyte using the halophytea as research material at present.This experiment designs universal primers for Halostachys caspica's miR417 coding sequences refering to Arabidopsis and rice's miR417 coding sequences which have been published. The whole genome of Halostachys caspica is as a template for polymerase chain reaction. The Halostachys caspica's miR417 coding sequences was got by polymerase chain reaction. The homologous analysis for nucleicacid between Halostachys caspica and Oryza sativa showed that their homologous is not high and the rate is less than 60%. This is similar to the homologous analysis for nucleicacid between Arabidopsis thaliana and Oryza sativa. The analysis of secondary sturcture showed that the pre-miRNA of Halostachys caspica is a stem-loop, which is little different from the pre-miRNA of Oryza sativa. The stem of Halostachys caspica's pre-miRNA is short than that of Oryza sativa's pre-miRNA. But the pre-miRNA of Halostachys caspica has a more loop at the end of the stem-loop.The plant expression vector of Halostachys caspica miR417 was constructed. Firstly, the empty plasmid pCAMBIA1301 was digested by Kpn I and Sal I and recoverid by Fragment DNA Agarose Gel Recovery Kit; Secondly, the synthetic single-strand annealed and the fragments with cohesive end was formd; Lastly, the target fragement was ligated to the vector successfully.Using Arabidopsis inflorescence DIP dip method, positive transgenic plants were obtained. First of all, the recombinant was transformed into Agrobacterium tumefaciens EHA105 competent cell. And then the genomic transformation of miR417 coden region into Arabidopsis thaliana mediated by Agrobacterium tumefaciens EHA105 was completed. Finally, the transgenic Arabidopsis thaliana's seedlings were aslo obtained successful by resistance selection using hygromycin.It's reported that miR417 may regulate the gene expression, such as At1g04150, At5g66460, At4g11130 and At3g06430, which are related to the salt-resistance. The overexpression plant can be uesd in the research on these genes . Halostachys caspica's sequence were obtained, which help construct the foundation of the study on Halostachys caspica's miR417 and the mechanism of salt-resistant.
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