基金
Supported by the National Natural Science Foundation of China （No. 20673014：20273010）. Acknowledgements： We are grateful to Dr. Zhu Ruiyan, from State Key Laboratory of Agro-biotechnology, China Agricultural University, for providing the strain of E. coli cell, and thanks should be given to Dr. Xin Mingxiu, from College of Life Science, Beijing Normal University, for his instrumental support for the culture of E. coil cell.
