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First published online October 15, 2004; 10.1104/pp.104.051508 Plant Physiology 136:3550-3561 (2004) © 2004 American Society of Plant Biologists Untranslated Regions from C4 Amaranth AhRbcS1 mRNAs Confer Translational Enhancement and Preferential Bundle Sheath Cell Expression in Transgenic C4 Flaveria bidentis1Department of Biological Sciences, The State University of New York at Buffalo, Buffalo, New York 14120 (M.P., A.C.C., J.O.B.); Department of Biology, Capital Normal University, Beijing 100037, China (L-P.Y.); and Commonwealth Scientific and Industrial Research Organization Division of Plant Industry, Canberra 2601, Australia (S.A., W.C.T.)
Many aspects of photosynthetic gene expression are posttranscriptionally regulated in C4 plants. To determine if RbcS mRNA untranslated regions (UTRs) in themselves could confer any characteristic C4 expression patterns, 5'- and 3'-UTRs of AhRbcS1 mRNA from the C4 dicot amaranth were linked to a gusA reporter gene. These were constitutively transcribed from a cauliflower mosaic virus promoter and assayed for posttranscriptional expression patterns in transgenic lines of the C4 dicot Flaveria bidentis. Three characteristic C4 expression patterns were conferred by heterologous AhRbcS1 UTRs in transgenic F. bidentis. First, the AhRbcS1 UTRs conferred strong translational enhancement of gusA expression, relative to control constructs lacking these UTRs. Second, while the UTRs did not appear to confer tissue-specific expression when analyzed by
1 This work was supported by the National Science Foundation (grant nos. INT 9724775 and MCB 0110411 to J.O.B.), the U.S. Department of Agriculture National Research Initiative (grant no. 2001–01825 to J.O.B.), and an academic exchange fellowship program from the University at Buffalo and Capitol Normal University (to L-P.Y.). 2 Present address: Department of Cell and Structural Biology, University of Illinois, 190 Edward R. Madigan Laboratories (ERML), 1201 W. Gregory Drive, Urbana, IL 61801. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.051508. * Corresponding author; e-mail camjob{at}buffalo.edu; fax: 716–645–3369. Received August 17, 2004; returned for revision September 7, 2004; accepted September 7, 2004. This article has been cited by other articles:
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-glucuronidase activity assays, differences in gusA mRNA accumulation were observed in leaves, stems, and roots. Third, the AhRbcS1 UTRs conferred preferential gusA expression (enzyme activity and gusA mRNA accumulation) in leaf bundle sheath cells. AhRbcS1 UTR-mediated translational enhancement was also observed in transgenic C3 plants (tobacco [Nicotiana tabacum]) and in in vitro translation extracts. These mRNAs appear to be translated with different efficiencies in C4 versus C3 plants, indicating that processes determining overall translational efficiency may vary between these two categories of higher plants. Our findings suggest that the AhRbcS1 5'-UTR functions as a strong translational enhancer in leaves and other tissues, and may work synergistically with the 3'-UTR to modulate overall levels of Rubisco gene expression in different tissues and cell types of C4 plants. 
