Cloning of cDNA Encoding Choline Monooxygenase from Suaeda liaotungensis and Salt Tolerance of Transgenic Tobacco

Betaine is a very effective osmoprotectant found in many organisms. In high plants, betaine is synthesized by oxidation of choline in two sequential steps: choline-->betaine aldehyde-->betaine. The first step is catalyzed by choline monooxygenase (CMO). In this study, the full-length CMO cDNA (1 820 bp) was cloned from halophyte Suaeda liaotungensis Kitag by RT-PCR and RACE. It included a 123 bp 5' UTR, a 368 bp 3' UTR and a 1 329 bp open reading frame encoding a 442-amino-acid polypeptide with 77%, 72% and 74% sequence identity compared to CMOs from spinach, sugar beet and Atriplex hortensis, respectively. The CMO open reading frame (ORF) was cloned and the plant expression vector pBI121-CMO was constructed. It was transferred into tobacco ( Nicotiana tabacum L. ev. 89) via Agrobacterium mediation. PCR and Southern blotting analysis showed that the CMO gene was integrated into tobacco genome. Transgenic tobacco plants contained higher amount of betaine than that of control plants and were able to survive on MS medium containing 250 mmol/L NaCl. Relative electronic conductivity demonstrated less membrane damage in transgenic plants as in the wild type.

Isolation of a choline monooxygenase cDNA clone from Amaranthus tricolor and its expressions under stress conditions

Plants synthesize the osmoprotectant glycine betaine (GB) via choline→betaine aldehyde→glycine be- taine[1]. Two enzymes are involved in the pathway choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH). A full length CMO cDNA (1,643bp) was cloned from Amaranthus tricolor. The open reading frame encoded a 442-amino acid polypeptide, which showed 69% identity with CMOs in Spina- cia oleracea L. and Beta vulgaris L. DNA gel blot analysis indicated the presence of one copy of CMO gene in the A. tricolor genome. The expressions of CMO and BADH proteins in A.tricolor leaves significantly increased under salinization, drought and heat stress (42℃), as determined by immunoblot analysis, but did not respond to cold stress (4℃), or exogenous ABA application. The increase of GB content in leaves was parallel to CMO and BADH contents.

Rapid Amplification of 5′ cDNA End of S. Liaotungensis Choline Monooxygenase Using Inverse PCR RACE

Based on part of a known cDNA sequence of Suaeda Liaotungensis choline monooxygenase, the authors successfully cloned the 5′ cDNA end of Suaeda Lianotungensis choline monooxygenase using Inverse PCR RACE with a specially designed 5′-phosphated RT primer and two pairs of specific inverse PCR primers. Compared with the anchored PCR RACE, inverse PCR RACE has better specificity and higher amplification.

Isolation and Characterization of CMO Gene Promoter from Halophyte Suaeda liaotungensis K.

The 5＇-flanking proximal region of stress-induced gene encoding choline monooxygenase （CMO） was isolated by Adaptor-PCR and TAIL-PCR from halophyte Suaeda liaotungensis K. A total of 2,204 bp DNA sequence was obtained. The transcription start site, which is located at 128 bp upstream to the start ATG, was predicted by the TSSP-TCM program. The functional elements were analysed by PLACE program. The obtained SICMO gene promoter contains the basic elements： TATA-box, CAAT-box, and stress-induced elements, for example, salt responsive element （GAAAAA）, cold responsive elements （CANNTG）, ABA （Abscisic Acid） responsive elements （NAACAA）, water stress element （CGGTTG）, and WUN responsive elements （GTTAGGTTC）. Isolation and analysis of the promoter of the CMO gene from S. liaotungensis lays a foundation for characterising the stress-induced promoter elements, studying the relationship between the structure and function of the promoter, and investigating the molecular mechanism of CMO gene regulation.