Browsing by Author "Figueroa, P"

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    The four subunits of mitochondrial respiratory complex II are encoded by multiple nuclear genes and targeted to mitochondria in Arabidopsis thaliana
    (2002) Figueroa, P; Léon, G; Elorza, A; Holuigue, L; Araya, A; Jordana, X
    Mitochondrial respiratory complex II contains four subunits: a flavoprotein (SDH1), an iron-sulphur subunit (SDH2) and two membrane anchor subunits (SDH3 and SDH4). We have found that in Arabidopsis thaliana SDH1 and SDH3 are encoded by two, and SDH4 by one nuclear genes, respectively. All these encoded polypeptides are found to be imported into isolated plant mitochondria. While both SDH1 proteins are highly conserved when compared to their counterparts in other organisms, SDH3 and SDH4 share little similarity with non-plant homologues. Expression of SDH1-1, SDH3 and SDH4 genes was detected in all tissues analysed, with the highest steady-state mRNA levels found in flowers and inflorescences. In contrast, the second SDH1 gene (SDH1-2) is expressed at a low level.
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    Three different genes encode the iron-sulfur subunit of succinate dehydrogenase in Arabidopsis thaliana
    (2001) Figueroa, P; León, G; Elorza, A; Holuigue, L; Jordana, X
    The iron-sulfur protein is an essential component of mitochondrial complex II (succinate dehydrogenase, SDH), which is a functional enzyme of both the citric acid cycle and the respiratory electron transport chain. This protein is encoded by a single-copy nuclear gene in mammals and fungi and by a mitochondrial gene in Rhodophyta and the protist Reclinomonas americana. In Arabidopsis thaliana, the homologous protein is now found to be encoded by three nuclear genes. Two genes (sdh2-1 and sdh2-2) likely arose from a relatively recent duplication event since they have similar structures, encode nearly identical proteins and show similar expression patterns. Both genes are interrupted by a single intron located at a conserved position. Expression was detected in all tissues analysed, with the highest steady-state mRNA levels found in flowers and inflorescences. In contrast, the third gene (sdh2-3) is interrupted by 4 introns, is expressed at a low level, and encodes a SDH2-3 protein which is only 67% similar to SDH2-1 and SDH2-2 and has a different N-terminal presequence. Interestingly, the proteins encoded by these three genes are probably functional because they are highly conserved compared with their homologues in other organisms. These proteins contain the cysteine motifs involved in binding the three iron-sulfur clusters essential for electron transport. Furthermore, the three polypeptides are found to be imported into isolated plant mitochondria.
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    Transfer of RPS14 and RPL5 from the mitochondrion to the nucleus in grasses
    (2004) Sandoval, P; León, G; Gómez, I; Carmona, R; Figueroa, P; Holuigue, L; Araya, A; Jordana, X
    Gene transfer from the mitochondrion to the nucleus, a process of outstanding importance to the evolution of the eukaryotic cell, is an ongoing phenomenon in higher plants. After transfer, the mitochondrial gene has to be adapted to the nuclear context by acquiring a new promoter and targeting information to direct the protein back to the organelle. To better understand the strategies developed by higher plants to transfer organellar genes during evolution, we investigated the fate of the mitochondrial PPL5-RPS14 locus in grasses. While maize mitochondrial genome does not contain RPS14 and RPL5 genes, wheat mitochondrial DNA contains an intact RPL5 gene and a nonfunctional RPS14 pseudogene. RPL5 and psiRPS14 are co-transcribed and their transcripts are edited. In wheat, the functional RPS14 gene is located in the nucleus, within the intron of the respiratory complex II iron-sulfur subunit gene (SDH2). Its organization and expression mechanisms are similar to those previously described in maize and rice, allowing us to conclude that RPS14 transfer and nuclear activation occurred before divergence of these grasses. Unexpectedly, we found evidence for a more recent RPL5 transfer to the nucleus in wheat. This nuclear wheat RPL5 acquired its targeting information by duplication of an existing targeting presequence for another mitochondrial protein, ribosomal protein L4. Thus, mitochondrial and nuclear functional RPL5 genes appear to be maintained in wheat, supporting the hypothesis that in an intermediate stage of the transfer process, both nuclear and mitochondrial functional genes coexist. Finally, we show that RPL5 has been independently transferred to the nucleus in the maize lineage and has acquired regulatory elements for its expression and a mitochondrial targeting peptide from an unknown source. (C) 2003 Elsevier B.V. All rights reserved.
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    Transfer of rps14 from the mitochondrion to the nucleus in maize implied integration within a gene encoding the iran-sulphur subunit of succinate dehydrogenase and expression by alternative splicing
    (1999) Figueroa, P; Gómez, I; Holuigue, L; Araya, A; Jordana, X
    The maize mitochondrial genome does not contain a gene coding for ribosomal protein S14. In this paper we show that the functional rps14 gene was translocated to the nucleus and acquired the signals conferring expression and product targeting to the mitochondrion in a way not previously described. Transferred rps14 was found integrated between both exons of a gene encoding the iron-sulphur subunit of the respiratory complex II (sdh2). Sdh2 exon 1 and rps14 were separated by a typical plant nuclear intron that was spliced to give a mature poly(A)+ mRNA of 1.4 kb. This processed mRNA encoded a chimeric SDH2 (truncated)-RPS14 polypeptide, and we show that this chimeric polypeptide is targeted into isolated plant mitochondria, where it is proteolytically processed in a complex way. An alternative splicing event utilizing the same 5' splice site and a different downstream 3' splice site generated a second mature poly(A)+ mRNA of 1.3 kb that contained both sdh2 exons. This sdh2 transcript encoded an SDH2 polypeptide highly conserved compared with its homologues in other organisms, and it contained the three cysteine-rich clusters that made up the three nonheme iron-sulphur centres responsible for electron transport. To our knowledge, these results constitute the first evidence of alternative splicing playing a role in the expression and targeting of two mitochondrial proteins with different functions from the same gene.