IDENTIFICATION OF A FUNCTIONAL HOMOLOG OF THE YEAST COPPER HOMEOSTASIS GENE ATX1 FROM ARABIDOPSIS

A cDNA clone encoding a homolog of the yeast (Saccharomyces cerevisiae ) gene Anti-oxidant I (ATX1) has been identified from Arabidopsis. Thi s gene, referred to as Copper CHaperone (CCH), encodes a protein that is 36% identical to the amino acid sequence of ATX1 and has a 48-amino acid extension at the C-terminal end, which is absent from ATX1 homol ogs identified in animals. ATX1-deficient yeast (atx1) displayed a los s of high-affinity iron uptake. Expression of CCH in the atx1 strain r estored high-affinity iron uptake, demonstrating that CCH is a functio nal homolog of ATX1. When overexpressed in yeast lacking the superoxid e dismutase gene SOD1, both ATX1 and CCH protected the cell from the r eactive oxygen toxicity that results from superoxide dismutase deficie ncy. CCH was unable to rescue the sod1 phenotype in the absence of cop per, indicating that CCH function is copper dependent. In Arabidopsis CCH mRNA is present in the root, leaf, and inflorescence and is up-reg ulated 7-fold in leaves undergoing senescence. In plants treated with 800 nL/L ozone for 30 min, CCH mRNA levels increased by 30%. In excise d leaves and whole plants treated with high levels of exogenous CuSO4, CCH mRNA levels decreased, indicating that CCH is regulated different ly than characterized metallothionein proteins in Arabidopsis.