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Plant Physiology Preview Published on March 2, 2007; 10.1104/pp.107.095752
Received January 10, 2007 An Unusual Post-transcriptional Processing in Two Betaine Aldehyde Dehydrogenase (BADH) Loci of Cereal Crops Directed by Short-direct Repeats in Response to Stress Conditions
Ministry of Education Key Laboratory for Southwest Bio-resource and Eco-environment, College of Life Science, Sichuan University, Chengdu 610064, China; Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Institute of Biodiversity Science, Fudan University, Shanghai 200433, China; Institute of Crop Research, Sichuan Academy of Agricultural Sciences, Chengdu 610066, China; State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610064, China * Corresponding author; email: liuyongsheng1122{at}yahoo.com.cn.
Various abilities to synthesize and accumulate glycine betaine (GB) are crucial for angiosperms to develop salt and drought tolerances. In higher plants, GB is synthesized by a two-step oxidation of choline via an intermediate form of betaine aldehyde, and catalyzed by choline monooxygenase (CMO) and betaine aldehyde dehydrogenase (BADH). In this study, numerous truncated and/or recombinant transcripts of two BADH homologues resulted from an unusual post-transcriptional processing were detected in rice (Oryza sativa) and other cereal crops, including maize (Zea mays), wheat (Triticum aestivum) and barley (Hordeum vulgare). The observed events took place at the 5' exonic region, and led to the insertion of exogenous gene sequences and a variety of deletions that resulted in the removal of translation initiation codon, loss of functional domain and frame-shifts with premature termination by introducing stop codon. By contrast, the BADH transcripts from dicotyledonous species such as spinach (Spinacia oleracea), Arabidopsis (Arabidopsis thaliana), and tomato (Solanum lycopersicum), had correctly processed mRNA. This suggests the differentiation of post-transcriptional processing in BADH genes potentially contributes to the variation of GB synthesizing capacities among various plant species. In addition, comprehensive sequence analyses demonstrated that extensive sequence similarities (named as short-direct repeats, SDRs) are of paired presence surrounding the junctions of both the deletion and/or insertion sites in the unusual BADH transcripts. The sites selection for the deletion/insertion was altered in response to the stress conditions. This indicates that the sequence elements of SDRs are probably required for the recognition of the deletion/insertion sites.
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