Expression of the Arabidopsis thaliana cytochrome c gene cytc-1 in anthers and meristems is controlled by TCP-domain protein binding elements and an internal telomeric repeat.

WELCHEN, ELINA.; GONZALEZ, DANIEL H.

Obernai

Congreso; International Congress on Plant Mitochondrial Biology. ICPMB 2005.; 2005

Societé Francaise de Biologie Végétale.

The promoters of the Arabidopsis thaliana cytochrome c genes Cytc-1 (At1g22840) and Cytc-2 (At4g10040) were analyzed using plants transformed with fusions to the b-glucuronidase coding sequence. The Cytc-1 promoter directs specific expression in root and shoot meristems and in anthers, as deduced from histochemical staining of transformed plants. In turn, plants transformed with the Cytc-2 promoter fusions showed expression in vascular tissues of cotyledons, leaves, roots, and hypocotyls, and also in anthers. Quantitative measurements in extracts prepared from different organs indicated that expression of Cytc-1 is higher in flowers, while that of Cytc-2 is higher in leaves. The analysis of deletion mutants of the Cytc-1 promoter revealed that a segment located between -147 and -218 from the translation start site is required for expression. A set of 10-bp scanning mutations along this 72-bp fragment was used to map the presence of discrete regulatory elements. Mutagenesis of the region between -147 and -156 completely abolished expression. This region contains two copies of the site II motif (TGGGCC/T) of the type present in genes which are actively transcribed in proliferating cells (1). The Cytc-1 gene also shares with these other genes the presence of a downstream internal telomeric repeat or telo box (AAACCCTAA), located between -86 and -94. Point mutations in the site II motifs or the telo box either abolished or dramatically reduced expression, respectively. Proteins present in cauliflower nuclear extracts were able to specifically bind to the region of the Cytc-1 gene required for expression. In addition, recombinant proteins AtTCP20 and AtPur also showed specific binding to the regions containing the site II elements and the telo box. We propose that expression of the Cytc-1 gene in meristems and anthers is linked to cell proliferation through the elements described above. We have also noted the presence of closely located site II motifs in several genes encoding subunits of cytochrome c oxidase or proteins involved in its biogenesis. This suggests that these elements may be the target of factors that co-ordinate the expression of nuclear genes encoding components of this part of the mitochondrial respiratory chain.