title: A MEM1-like motif directs mesophyll cell-specific expression of the gene encoding the C4 carbonic anhydrase in Flaveria.
abstract: The first two reactions of C4photosynthesis are catalysed by carbonic anhydrase (CA) and phosphoenolpyruvate carboxylase (PEPC) in the leaf mesophyll (M) cell cytosol. Translatome experiments using a tagged ribosomal protein expressed under the control of M and bundle-sheath (BS) cell-specific promoters showed transcripts encoding CA3 from the C4species Flaveria bidentis were highly enriched in polysomes from M cells relative to those of the BS. Localisation experiments employing a CA3-green fluorescent protein fusion protein showed F. bidentis CA3 is a cytosolic enzyme. A motif showing high sequence homology to that of the Flaveria M expression module 1 (MEM1) element was identified approximately 2 kb upstream of the F. bidentis and F. trinervia ca3 translation start sites. MEM1 is located in the promoter of C4Flaveria ppcA genes, which encode the C4-associated PEPC, and is necessary for M-specific expression. No MEM1-like sequence was found in the 4 kb upstream of the C3species F. pringlei ca3 translation start site. Promoter-reporter fusion experiments demonstrated the region containing the ca3 MEM1-like element also directs M-specific expression. These results support the idea that a common regulatory switch drives the expression of the C4Flaveria ca3 and ppcA1 genes specifically in M cells.
authors.affiliation: Institute of Plant Molecular and Developmental Biology, Heinrich-Heine-University, Düsseldorf, Germany.
authors.forename: Udo
authors.initials: U
authors.lastname: Gowik
authors.affiliation: Institute of Plant Molecular and Developmental Biology, Heinrich-Heine-University, Düsseldorf, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Schulze
authors.affiliation: School of Chemistry and Biochemistry, University of Western Australia, Crawley, WA, Australia.
authors.forename: Montserrat
authors.initials: M
authors.lastname: Saladié
authors.affiliation: Australian Research Council Centre of Excellence for Translational Photosynthesis, Plant Science Division, Research School of Biology, Australian National University, Canberra, ACT, Australia.
authors.forename: Vivien
authors.initials: V
authors.lastname: Rolland
authors.affiliation: Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, WA, Australia.
authors.forename: Sandra K
authors.initials: SK
authors.lastname: Tanz
authors.affiliation: Institute of Plant Molecular and Developmental Biology, Heinrich-Heine-University, Düsseldorf, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Westhoff
authors.affiliation: School of Chemistry and Biochemistry, University of Western Australia, Crawley, WA, Australia martha.ludwig@uwa.edu.au.
authors.forename: Martha
authors.initials: M
authors.lastname: Ludwig
mesh_terms: D001483:Base Sequence; D037142:Flaveria / Q000201:enzymology* / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D058503:Mesophyll Cells / Q000201:enzymology*; D008969:Molecular Sequence Data
keywords: 
  Flaveria
  ; C4 photosynthesis; MEM1; carbonic anhydrase; evolution of C4 photosynthesis; gene expression; mesophyll cell expression; translatome.