title: Rice choline monooxygenase (OsCMO) protein functions in enhancing glycine betaine biosynthesis in transgenic tobacco but does not accumulate in rice (Oryza sativa L. ssp. japonica).
abstract: Glycine betaine (GB) is a compatible quaternary amine that enables plants to tolerate abiotic stresses, including salt, drought and cold. In plants, GB is synthesized through two-step of successive oxidations from choline, catalyzed by choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH), respectively. Rice is considered as a typical non-GB accumulating species, although the entire genome sequencing revealed rice contains orthologs of both CMO and BADH. Several studies unraveled that rice has a functional BADH gene, but whether rice CMO gene (OsCMO) is functional or a pseudogene remains to be elucidated. In the present study, we report the functional characterization of rice CMO gene. The OsCMO gene was isolated from rice cv. Nipponbare (Oryza sativa L. ssp. japonica) using RT-PCR. Northern blot demonstrated the transcription of OsCMO is enhanced by salt stress. Transgenic tobacco plants overexpressing OsCMO results in increased GB content and elevated tolerance to salt stress. Immunoblotting analysis demonstrates that a functional OsCMO protein with correct size was present in transgenic tobacco but rarely accumulated in wild-type rice plants. Surprisingly, a large amount of truncated proteins derived from OsCMO was induced in the rice seedlings in response to salt stresses. This suggests that it is the lack of a functional OsCMO protein that presumably results in non-GB accumulation in the tested rice plant.
  
  
  CONCLUSIONS
  Expression and transgenic studies demonstrate OsCMO is transcriptionally induced in response to salt stress and functions in increasing glycinebetaine accumulation and enhancing tolerance to salt stress. Immunoblotting analysis suggests that no accumulation of glycinebetaine in the Japonica rice plant presumably results from lack of a functional OsCMO protein.
authors.affiliation: Ministry of Education Key Laboratory for Bio-resource and Eco-environment, College of Life Science and State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu, 610064, China.
authors.forename: Di
authors.initials: D
authors.lastname: Luo
authors.forename: Xiangli
authors.initials: X
authors.lastname: Niu
authors.forename: Jinde
authors.initials: J
authors.lastname: Yu
authors.forename: Jun
authors.initials: J
authors.lastname: Yan
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Gou
authors.forename: Bao-Rong
authors.initials: BR
authors.lastname: Lu
authors.forename: Yongsheng
authors.initials: Y
authors.lastname: Liu
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001483:Base Sequence; D001622:Betaine / Q000378:metabolism*; D018533:Biomass; D015153:Blotting, Western; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant / Q000235:genetics; D008969:Molecular Sequence Data; D012275:Oryza / Q000187:drug effects / Q000201:enzymology*; D010105:Oxygenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism; D030821:Plants, Genetically Modified; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012965:Sodium Chloride / Q000494:pharmacology; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics; D014026:Nicotiana / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D024363:Transcription Initiation Site
chemical_list: D010940:Plant Proteins; D001622:Betaine; D012965:Sodium Chloride; C105448:choline monooxygenase; D010105:Oxygenases