Functional analysis of mitochondrial cytochrome c oxidase gene promoters in Arabidopsis thaliana

EDUARDO MUFARREGE; GRACIELA CURI; DANIEL GONZALEZ

Rosario- Santa Fe-Argentina

Otro; XIII Reunion Latinoamericana y XXVII Reunion Nacional de Fisiología Vegetal; 2008

Sociedad Argentina de Fisiología Vegetal

Cytochrome c oxidase (COX) is composed of several subunits, three of them encoded by the mitochondrial genome and the others encoded by the nuclear genome. In this work, we study the structure of the single COX6a and the three COX6b gene promoters from Arabidopsis thaliana. All of these promoters contain copies of a motif named site II (TGGGCC/T) involved in expression in proliferating cells in other genes. We obtained plants that express the gus (â-glucuronidase) gene under the control of COX6a and COX6b promoter sequences and we analyzed GUS enzymatic activity by histochemical and fluorometric assays. Plants with COX6a promoter sequences fused to gus revealed GUS activity only in pollen grains. The COX6b1/3 lines showed similar expression patterns in roots, cotyledon veins, leaf veins, shoot apical meristem and pollen. Deletions of the respective promoters down to approximately -200 (a fragment that included the site II motifs) produced plants with the same expression patterns as those observed with larger fragments. In plants that contained promoters with mutagenized site II motifs, the expression disappeared or was extremely low. Band shift assays using promoter fragments containing site II motifs or the respective mutagenized forms indicated the presence in nuclear extracts of common sets of proteins that interact with these motifs. We also analyzed the response of the four genes towards different factors. We found that all of them were induced when plants were grown in darkness and in the presence of sucrose. In addition, COX6b-1 and COX6b-3 expression increased in the presence of gibberellins and cytokinins, respectively. The response to darkness and sucrose was conserved upon deletion of the respective promoters down to -200, but was abolished after mutation of site II motifs. The results obtained suggest that site II motifs are required for expression of all Arabidopsis COX6 genes and may participate in the coordinated response of these genes to metabolic factors.