The promoters of Arabidopsis thaliana genes AtCOX17‐1 and ‐2, encoding a copper chaperone involved in cytochrome c oxidase biogenesis, are preferentially active in roots and anthers and induced by biotic and abiotic stress

Abstract

AtCOX17 genes encode Arabidopsis thaliana homologs of the yeast metallochaperone Cox17p, involved in the delivery of copper for cytochrome c oxidase (COX) assembly. Two different AtCOX17 genes, located in chromosomes 1 and 3, are present in the Arabidopsis genome. Sequences available in data banks indicate that the presence of two genes is a common feature in monocots, but not in dicots, suggesting that Arabidopsis genes may be the result of a recent duplication. Sequences upstream from the translation start sites of AtCOX17 genes, which include an intron located in the 5′ leader region, were introduced into plants in front of the gus gene. For both genes, expression was localized preferentially in young roots and anthers, but almost 10‐fold higher β‐glucuronidase activity levels were observed in plants transformed with AtCOX17‐1 upstream regions. Both promoters were induced to different extents by wounding, treatment of leaves with the bacterial pathogen Pseudomonas syringae and incubation with agents that produce oxidative stress and metals. AtCOX17‐2 showed similar responses to these factors, while AtCOX17‐1 was more strongly induced by relatively low (10–100 μM) copper. The results indicate that both AtCOX17 genes have similar, though not identical, expression characteristics and suggest the existence in their promoters of elements involved in tissue‐specific expression and in responses to factors that may produce mitochondrial or cell damage. It can be speculated that Arabidopsis COX17 accumulates under stress conditions to actively replace damaged or inactive cytochrome c oxidase to sustain cyanide‐sensitive respiration in plant cells.

Knock-down of the COX3 and COX17 gene expression of cytochrome c oxidase in the unicellular green alga Chlamydomonas reinhardtii

“…In Arabidopsis thaliana, the abundance of the COX17 mRNA is increased after short treatments with metals (Attallah et al 2007;Balandin and Castresana 2002). To determine if a similar situation is found in Chlamydomonas, exponentially growing cells were treated with a non-inhibiting concentration of CuSO 4 (250 lM, 4 h) or CdCl 2 (250 lM, 2 h; Hanikenne et al 2005).…”

“…This strengthens the suggestion that this protein could have additional essential function(s) in the cell. Because COX17 expression is induced following addition of pathogens or metals, the idea that Cox17 could be implicated in responses to stresses has already been proposed in higher plants (Attallah et al 2007;Balandin and Castresana 2002). To decipher the molecular mechanism in which Cox17 is implicated, one may try to find out possible loss of co-regulation between expression of COX17 and other genes involved in Cu/Cd excess or ROS signaling in our cox17-RNAi mutant by using q-RT-PCR and/or transcriptomics.…”

“…Two COX17 genes are present in the Arabidopsis genome and one of them was shown to encode a protein able to complement a cox17 yeast mutant (Balandin and Castresana 2002). Moreover, RNA abundance of both genes was induced by compounds or factors that produce stress, like metals or pathogens, which may indicate a relevant role of this protein in the biogenesis of cytochrome c oxidase to replace damaged forms of the enzyme or a more general role in the plant stress response (Attallah et al 2007;Balandin and Castresana 2002).…”

Characterization of Arabidopsis thaliana genes encoding functional homologues of the yeast metal chaperone Cox19p, involved in cytochrome c oxidase biogenesis

“…Our results suggest that, in addition to increasing the capacity of alternative respiration, plant cells induce proteins involved in the biogenesis of the cytochrome pathway, presumably to replace inactive components. In this sense, it has been observed that genes encoding another metallochaperone involved in COX assembly, AtCOX17, show very similar responses to stress factors (Balandin and Castresana 2002;Attallah et al 2007). In addition, the analysis of publicly available microarray data indicates that genes encoding homologues of other COX assembly factors, such as COX15 and SCO1, and a group of plantspecific COX subunits (COXX1, COXX6; Millar et al 2004) are also induced by pathogens and other stress factors.…”

Arabidopsis Pollen Fertility Requires the Transcription Factors CITF1 and SPL7 That Regulate Copper Delivery to Anthers and Jasmonic Acid Synthesis

“…In addition to Cu transporters, plantacyanins, which are classified as blue Cu proteins, have a conserved Cu binding site and are involved in pollen germination and pollen tube guidance (Rydén and Hunt, 1993;Einsle et al, 2000). Finally, Arabidopsis cytochrome c oxidase biogenesis factor 17 is expressed in anthers and roots (Attallah et al, 2007). These data suggest that Cu must function in anthers of Arabidopsis; however, the localization of Cu in plant reproductive structures has not been determined experimentally.…”