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GENETICS, GENOMICS, AND MOLECULAR EVOLUTION

The Gene for the P-Subunit of Glycine Decarboxylase from the C₄ Species Flaveria trinervia: Analysis of Transcriptional Control in Transgenic Flaveria bidentis (C₄) and Arabidopsis (C₃)^1,[W],[OA]

Institut für Entwicklungs- und Molekularbiologie der Pflanzen, Heinrich-Heine-Universität, 40225 Duesseldorf, Germany (S.E., C.W., J.B., U.G., U.S., M.K., M.S., P.W.); Institute of Plant Genetics and Crop Plant Research (IPK), 06466 Gatersleben, Germany (R.C.); and Abteilung Pflanzenphysiologie der Universität Rostock, 18051 Rostock, Germany (H.B.)

Glycine decarboxylase (GDC) plays an important role in the photorespiratory metabolism of plants. GDC is composed of four subunits (P, H, L, and T) with the P-subunit (GLDP) serving as the actual decarboxylating unit. In C₃ plants, GDC can be found in all photosynthetic cells, whereas in leaves of C₃-C₄ intermediate and C₄ species its occurrence is restricted to bundle-sheath cells. The specific expression of GLDP in bundle-sheath cells might have constituted a biochemical starting point for the evolution of C₄ photosynthesis. To understand the molecular mechanisms responsible for restricting GLDP expression to bundle-sheath cells, we performed a functional analysis of the GLDPA promoter from the C₄ species Flaveria trinervia. Expression of a promoter-reporter gene fusion in transgenic plants of the transformable C₄ species Flaveria bidentis (C₄) showed that 1,571 bp of the GLDPA 5' flanking region contain all the necessary information for the specific expression in bundle-sheath cells and vascular bundles. Interestingly, we found that the GLDPA promoter of F. trinervia exhibits a C₄-like spatial activity also in the C₃ plant Arabidopsis (Arabidopsis thaliana), indicating that a mechanism for bundle-sheath-specific expression is also present in this C₃ species. Using transgenic Arabidopsis, promoter deletion studies identified two regions in the GLDPA promoter, one conferring repression of gene expression in mesophyll cells and one functioning as a general transcriptional enhancer. Subsequent analyses in transgenic F. bidentis confirmed that these two segments fulfill the same function also in the C₄ context.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Peter Westhoff (west{at}uni-duesseldorf.de).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.114462

^* Corresponding author; e-mail west{at}uni-duesseldorf.de.

Received December 2, 2007; accepted February 17, 2008; published February 27, 2008.

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