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J Exp Bot. 2017 Jan;68(2):311-320. doi: 10.1093/jxb/erw475. Epub 2016 Dec 30.

A MEM1-like motif directs mesophyll cell-specific expression of the gene encoding the C4 carbonic anhydrase in Flaveria.

Author information

1
Institute of Plant Molecular and Developmental Biology, Heinrich-Heine-University, Düsseldorf, Germany.
2
School of Chemistry and Biochemistry, University of Western Australia, Crawley, WA, Australia.
3
Australian Research Council Centre of Excellence for Translational Photosynthesis, Plant Science Division, Research School of Biology, Australian National University, Canberra, ACT, Australia.
4
Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, WA, Australia.
5
School of Chemistry and Biochemistry, University of Western Australia, Crawley, WA, Australia martha.ludwig@uwa.edu.au.

Abstract

The first two reactions of C4 photosynthesis 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 C4 species 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 C4 Flaveria 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 C3 species 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 C4 Flaveria ca3 and ppcA1 genes specifically in M cells.

KEYWORDS:

Flaveria ; C4 photosynthesis; MEM1; carbonic anhydrase; evolution of C4 photosynthesis; gene expression; mesophyll cell expression; translatome.

PMID:
28040798
PMCID:
PMC5853542
DOI:
10.1093/jxb/erw475
[Indexed for MEDLINE]
Free PMC Article

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