Isolation of choline monooxygenase (CMO) gene from Salicornia europaea and enhanced salt tolerance of transgenic tobacco with CMO genes.

Glycinebetaine (GB) is an osmoprotectant accumulated by certain plants in response to high salinity, drought, and cold stress. Plants synthesize GB via the pathway choline --> betaine aldehyde --> glycinebetaine, and the first step is catalyzed by choline monooxygenase (CMO). In the present study, by using RT-PCR and RLM-RACE, a full-length CMO cDNA (1844 bp) was cloned from a halophyte Salicornia europaea, which showed high homology to other known sequences. In order to identify its function, the ORF of CMO cDNA was inserted into binary vector PBI121 to construct the chimeric plant expression vector PBI121-CMO. Using Agrobacterium (LBA4404) mediation, the recombinant plasmid was transferred into tobacco (Nicotiana tabacum). The PCR, Southern blot and RT-PCR analysis indicated the CMO gene was integrated into the tobacco genome, as well as expressed on the level of transcription. The transgenic tobacco plants were able to survive on MS medium containing 300 mmol/L NaCl and more vigorous than those of wild type with the same concentration salt treatment. In salt-stress conditions, transgenic plants had distinctly higher chlorophyll content and betaine accumulation than that of the control, while relative electrical conductivity of transgenic plants was generally lower. The results suggested the CMO gene transformation could effectively contribute to improving tobacco salt-resistance.