Respiration Arabidopsis homologues of mitochondrial copper chaperones SCO1, COX17 and COX19: More than COX assembly factors

GONZALEZ, D.H.; GARCIA, L.; WELCHEN, E.; ATTALLAH, C.V.

Fulda

Congreso; International Conference for Plant Molecular Biology; 2011

The Arabidopsis genome encodes putative homologues of mitochondrial proteins involved in copper delivery and insertion into cytochrome c oxidase (COX) in other organisms. Two Arabidopsis genes (HCC1 and HCC2), resulting from a duplication that occurred before the emergence of flowering plants, encode proteins with homology to SCO proteins, that participate in copper insertion into COX2. Mutation of HCC1 is embryo lethal and these embryos lack COX activity, suggesting that HCC1 participates in COX assembly. On the contrary, homozygote HCC2 mutant plants develop normally and do not show changes in COX2 levels. These plants display increased sensitivity of root growth to increased copper and higher expression of miR398 and other genes that respond to copper limitation, in spite of the fact that they have a higher copper content than wild-type. HCC2 mutant plants also show increased expression of stress-responsive genes. The results suggest that HCC1 is the protein involved in COX biogenesis and that HCC2, that lacks the cysteines and histidine putatively involved in copper binding, functions in copper sensing and redox homeostasis. We have also studied the function of COX17 and COX19, two soluble copper chaperones from the intermembrane space, using artificial miRNAs to reduce their expression levels. Plants with reduced levels of COX17 and COX19 show normal COX2 levels, induction of the copper chaperone CCH and repression of COPT2, a transporter induced by copper deficiency. These plants also show reduced expression levels of the stress-responsive genes APX1 and CAT3, increased lipid peroxidation and increased sensitivity to high concentrations of mannitol and NaCl. Overexpression of COX17 and COX19 produces the induction of low-copper responsive genes and increased tolerance to stress conditions. We postulate that these mitochondrial copper chaperones have roles beyond COX biogenesis and participate in the regulation of copper and redox homeostasis within plant cells.