Arabidopsis thaliana Oxa proteins locate to mitochondria and fulfill essential roles during embryo development

Abstract

Members of the Alb3/Oxa1/YidC protein family function as insertases in chloroplasts, mitochondria, and bacteria. Due to independent gene duplications, all organisms possess two isoforms, Oxa1 and Oxa2 except gram-negative bacteria, which encode only for one YidC-like protein. The genome of Arabidopsis thaliana however, encodes for eight different isoforms. The localization of three of these isoforms has been identified earlier: Alb3 and Alb4 located in thylakoid membranes of chloroplasts while AtOxa1 was found in the inner membrane of mitochondria. Here, we show that the second Oxa1 protein, Oxa1b as well as two Oxa2 proteins are also localized in mitochondria. The last two isoforms most likely encode truncated versions of Oxa-like proteins, which might be inoperable pseudogenes. Homozygous mutant lines were only obtained for Oxa1b, which did not reveal any significant phenotypes, while T-DNA insertion lines of Oxa1a, Oxa2a and Oxa2b resulted only in heterozygous plants indicating that these genes are indispensable for plant development. Phenotyping heterozygous lines showed that embryos are either retarded in growth, display an albino phenotype or embryo formation was entirely abolished suggesting that Oxa1a and both Oxa2 proteins function in embryo formation although at different developmental stages as indicated by the various phenotypes observed.

Phenotype to genotype using forward-genetic Mu-seq for identification and functional classification of maize mutants

“…Four of the seven candidate genes are predicted to modulate that process at some level (Table 5). This finding is analogous to that of a growing number of studies pointing to prominent roles of organellar function in embryogenesis and seed development (McElver et al, 2001; Schmitz-Linneweber and Small, 2008; Myouga et al, 2010; Bryant et al, 2011; Steinnebrunner et al, 2011; Holdorf et al, 2012; Benz et al, 2013). …”

OXA2b is Crucial for Proper Membrane Insertion of COX2 during Biogenesis of Complex IV in Plant Mitochondria

“…For comparison, a selection of bacterial YidC and chloroplast Alb3/Alb4 sequences were also included in the phylogenetic analysis. As observed in Benz et al (2013), YidC and Alb3/Alb4 proteins were more closely related and clustered together on one side (Fig. 2).…”

“…The Oxa1 super family is well conserved from a structural and mechanistic standpoint, although conservation can be quite low at sequence level (Anghel et al, 2017). Previous attempts to determine whether OXA2b is more closely related to yeast or mammalian Oxa1 or Cox18 were limited to small data sets (Benz et al, 2013). To overcome this limitation, Oxa1-like proteins of all plant species found in the Phytozome database were used to create an unrooted phylogenetic tree ( Fig.…”

“…Plants have four Oxa homologs, OXA1a, OXA1b, OXA2a, and OXA2b, which were all confirmed to be localized within the mitochondrial inner membrane using a combination of GFP tagging and in vitro import experiments (Sakamoto et al, 2000;Benz et al, 2013). Homozygous T-DNA lines of OXA1a, OXA2a, and OXA2b aborted at early stages of embryogenesis (Benz et al, 2013), indicating that each of them performs essential functions during mitochondrial biogenesis. Interestingly, plant mitochondrial OXA2a and OXA2b have a tetratricopeptide repeat (TPR) domain at the C terminus that is not found in any other known homolog of Cox18 or the Oxa1/YidC/Alb3 protein family ( Fig.…”

“…Interestingly, plant mitochondrial OXA2a and OXA2b have a tetratricopeptide repeat (TPR) domain at the C terminus that is not found in any other known homolog of Cox18 or the Oxa1/YidC/Alb3 protein family ( Fig. 1; Benz et al, 2013;Kolli et al, 2018). TPR domains serve as scaffolds for protein-protein interactions in a variety of cellular functions, including mitochondrial precursor targeting and translocation (Blatch and Lässle, 1999;Fan and Young, 2011).…”