Journal
PLANT PHYSIOLOGY
Volume 146, Issue 4, Pages 1773-1785Publisher
AMER SOC PLANT BIOLOGISTS
DOI: 10.1104/pp.107.114462
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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 C-3 plants, GDC can be found in all photosynthetic cells, whereas in leaves of C-3-C-4 intermediate and C-4 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 C-4 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 C-4 species Flaveria trinervia. Expression of a promoter-reporter gene fusion in transgenic plants of the transformable C-4 species Flaveria bidentis (C-4) 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 C-4-like spatial activity also in the C-3 plant Arabidopsis (Arabidopsis thaliana), indicating that a mechanism for bundle-sheath-specific expression is also present in this C-3 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 C-4 context.
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