Is it easy to become C2? - Molecular components and evolutionary significance of Gldp promoter regulation in Arabidopsis thaliana

• Applicant: Professorin Dr. Jutta Papenbrock, since 4/2017
• Subject Area: Plant Physiology ; Plant Genetics and Genomics
• Term: from 2015 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 271649190

Limitation of glycine decarboxylase (GDC) activity to bundle sheath (BS) cells was an important step during the evolution of C4 plants. Some plants called C2 plants or C3-C4 intermediates still use this mechanism to enhance the refixation of carbon dioxide released in photorespiration. Current evidence suggests that restriction of the expression of the gene encoding the P subunit of GDC (Gldp) was used to move GDC to the BS in independent evolutionary lineages. In Arabidopsis, a classical C3 plant, the GLDP protein is encoded by the two functionally redundant genes Gldp1 and Gldp2, that are both expressed in mesophyll (M) and BS cells. Using promoter-reporter fusions, we observed that deletion of an upstream promoter element was sufficient to eliminate expression of both Gldp1 and Gldp2 in Arabidopsis M cells and, thus, to resemble the expression pattern found in C2 and C4 plants. We pinned down the responsible M box to 60 bp. A 13 bp sequence in this region is highly conserved in the Brassicaceae family. The M box coincides with a region of low nucleosome occupancy on the promoter. In this project, we want to define the minimal M box motif and identify trans-acting M box binding factors (MBBF). Overexpression and mutation of MBBF genes will be used to characterize their function. We will further restrict expression of the GLDP protein to BS cells by expression of a BS-specific version of Gldp1 in Arabidopsis gldp mutants and study the physiology of these plants. In addition, expression of the intact Arabidopsis Gldp1 promoter and the BS-specific version will be studied in Gynandropsis gynandra, the nearest C4 relative to Arabidopsis. The analysis of Gldp promoters will be extended to rice in order to identify a M box homologue in a grass species, by this enabling us to make use of the ever growing collection of C3, C2 and C4 genome sequences in the Poaceae for comparative genomics. These analyses will provide mechanistic insights into the evolution of C2 and C4 metabolism.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Professor Dr. Christoph Peterhänsel, until 4/2017