Browsing by Author "Araya, A"

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    Editing status of mat-r transcripts in mitochondria from two plant species
    (1998) Bégu, D; Mercado, A; Farré, JC; Moenne, A; Holuigue, L; Araya, A; Jordana, X
    The intronic mat-r ORF encodes a protein with significant homology to retroviral reverse transcriptases. Here, we describe the nucleotide sequence of potato mat-r and study the editing status of mat-r transcripts in two systems, potato and wheat, where the mat-r ORF is part of the trans-introns but in two different configurations relative to nadl exons d and e. In potato and wheat, 13 and 15 C-to-U transitions respectively were observed. Most transcripts were partially edited, but potato transcripts were edited more efficiently than wheat transcripts. As in functional mitochondrial genes, RNA editing increased the similarity between plant mat-r proteins and their homologous non-plant counterparts. Interestingly, editing of mat-r was clustered in the reverse-transcriptase (RT) and the maturase (X) domains, two well defined regions having known functions in other systems. These results, together with the integrity and sequence conservation of mat-r, strongly suggest that the encoded protein plays a functional role in plant mitochondria.
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    Estimation of the number of institutionalized elderly in Chile
    (SOC MEDICA SANTIAGO, 2004) Marin, PP; Guzman, JM; Araya, A
    Background: Elderly people (>60 years) in Chile represented 11.4% (n = 1,717,478) of the total population in 2002. The group with disabilities or mental problems is increasing and there is no reliable information about the number of institutionalized elderly subjects. Aim: To estimate the number of elderly people living in residences for long term care and their and main characteristics. Patients and methods: Chilean Census does not provide: exact information about institutional care, therefore; we developed "proxy" indicator of the: percentage of institutionalized elderly (those living in "collective residences with more than 5 elderly persons and in which they represent more than 25% of the residents". This proxy has a R2=0.9859 with the true value of institutionalized persons for those Latin-American countries with exact value in census data at CELADE. Results: Using the proxy we found that institutionalized elderly population had increased,from. 14,114 (1992) to 26,854 (2002) and is projected to reach 83,500 (2025). In 2002, there were 1,668 institutions (37.4% informal care). In the Metropolitan Area, there were 804 institutions (14,178 elderly persons) and 40.3% of these were registered at the Ministry of Health. The proportion of institutionalized elderly subjects was 1.56% of the total elderly population; this proportion increased from 0.87% in subjects 60-74 years old to 2.5% among subjects aged 75-84 years and 6.1% in subjects 85 years old and over. Among subjects living in institutions, 60.9 were women, 21% were married, 35% were single, approximately 50% receive a pension and around 15% were handicapped. Conclusions: Institutional care affects a small percentage of elderly population, but it will increase to the near future. The main characteristics of institutionalized elderly subjects are not well known. We propose to create a formal Registry of these institutions and to include Nursing Homes and hospitals in type of housing of future Censuses.
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    Gene expression studies in isolated mitochondria
    (2005) Choury, D; Farré, JC; Jordana, X; Araya, A
    The complex gene expression mechanisms that occur in plant mitochondria, such as RNA editing and splicing, are not yet well understood. RNA editing in higher plant mitochondria is a highly specific process which modifies mRNA sequences by C-to-U conversions. It has been suggested that in some cases this process is required for splicing. Here, we use an experimental model based on the introduction of DNA into isolated mitochondria by electroporation to study organellar gene expression events. Our aim was to compare processing and editing of potato small ribosomal protein 10 gene (rps10) transcripts in heterologous (wheat mitochondria) and homologous (potato mitochondria) contexts. rps10 is a suitable model because it contains a group II intron, is absent in wheat mitochondria but is actively expressed in potato mitochondria, where transcripts are spliced and undergo five C-to-U editing events. For this purpose, conditions for electroporating isolated potato mitochondria were established. rps10 was placed under the control of either potato or wheat cox2 promoters. We found that rps10 was only transcribed under the control of a cognate promoter. In wheat mitochondria, rps10 transcripts were neither spliced nor edited while they are correctly processed in potato mitochondria. Interestingly, a wheat editing site grafted into rps10 was not recognized by wheat mitochondria but was correctly edited in potato mitochondria. Taken together, these results suggest that editing might occur only when the transcripts are engaged in processing and that they would not be available to editing factors outside of a putative RNA maturation machinery complex.
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    cis recognition elements in plant mitochondrion RNA editing
    (2001) Farré, JC; Leon, G; Jordana, X; Araya, A
    RNA editing in higher plant mitochondria modifies mRNA sequences by means of C-to-U conversions at highly specific sites. To determine the cis elements involved in recognition of an editing site in plant mitochondria, deletion and site-directed mutation constructs containing the cognate cox II mitochondrial gene were introduced into purified mitochondria by electroporation. The RNA editing status was analyzed for precursor and spliced transcripts from the test construct. We found that only a restricted number of nucleotides in the vicinity of the target C residue were necessary for recognition by the editing machinery and that the nearest neighbor 3 ' residues were crucial for the editing process. We provide evidence that two functionally distinguishable sequences can be defined: the 16-nucleotide 5 ' region, which can be replaced with the same region from another editing site, and a 6-nucleotide 3 ' region specific to the editing site. The latter region may play a role in positioning the actual editing residue.
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    Nuclear SDH2-1 and SDH2-2 genes, encoding the iron-sulfur subunit of mitochondrial complex II in arabidopsis, have distinct cell-specific expression patterns and promoter activities
    (2004) Elorza, A; León, G; Gómez, I; Mouras, A; Holuigue, L; Araya, A; Jordana, X
    Three different nuclear genes encode the essential iron-sulfur subunit of mitochondrial complex 11 (succinate dehydrogenase) in Arabidopsis (Arabidopsis thaliana), raising interesting questions about their origin and function. To find clues about their role, we have undertaken a detailed analysis of their expression. Two genes (SDH2-1 and SDH2-2) that likely arose via a relatively recent duplication event are expressed in all organs from adult plants, whereas transcripts from the third gene (SDH2-3) were not detected. The tissue- and cell-specific expression of SDH2-1 and SDH2-2 was investigated by in situ hybridization. In flowers, both genes are regulated in a similar way. Enhanced expression was observed in floral meristems and sex organ primordia at early stages of development. As flowers develop, SDH2-1 and SDH2-2 transcripts accumulate in anthers, particularly in the tapetum, pollen mother cells, and microspores, in agreement with an essential role of mitochondria during anther development. Interestingly, in contrast to the situation in flowers, only SDH2-2 appears to be expressed at a significant level in root tips. Strong labeling was observed in all cell layers of the root meristematic zone, and a cell-specific pattern of expression was found with increasing distance from the root tip, as cells attain their differentiated state. Analysis of transgenic Arabidopsis plants carrying SDH2-1 and SDH2-2 promoters fused to the beta-glucuronidase reporter gene indicate that both promoters have similar activities in flowers, driving enhanced expression in anthers and/or pollen, and that only the SDH2-2 promoter is active in root tips. These beta-glucuronidase staining patterns parallel those obtained by in situ hybridization, suggesting transcriptional regulation of these genes. Progressive deletions of the promoters identified regions important for SDH2-1 expression in anthers and/or pollen and for SDH2-2 expression in anthers and/or pollen and root tips. Interestingly, regions driving enhanced expression in anthers are differently located in the two promoters.
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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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    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.