Browsing by Author "Elorza, A"

Now showing 1 - 4 of 4
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    Identification and characterization of a novel tobacco mosaic virus resistance N gene homologue in Nicotiana tabacum plants
    (2004) Stange, C; Matus, JT; Elorza, A; Arce-Johnson, P
    Nicotiana tabacum cv. Xanthi nn plants are susceptible to infection by most tobamoviruses (TMV). However, such plants display a partial hypersensitive resistance response (HR-like response) to TMV-Cg. The genetic mechanism of the HR-like response has yet not been determined, but it may involve a gene with a function similar to that of a resistance gene, responsible for HR in resistant plants. We have cloned a gene homologous to the resistance N gene, named NH, from Nicotiana Xanthi nn plants. The coding region of NH is 5.028 base pairs ( bp) long and has 82.6% nucleotide identity with the N gene. In contrast to the N gene, the NH gene lacks intron 4 and does not have sites for alternative splicing of intron 3. Analysis of its sequence revealed that NH belongs to the TIR/NSB/LRR gene class. We were able to detect stable levels of NH-transcript in Nicotiana Xanthi nn plants from 0 to 18 h post-inoculation (hpi) with TMV-Cg. Transcript levels increased slightly at 24 hpi and dropped below basal values at 48 hpi. The NH transcript was also detected in a range of resistant Nicotiana plants ( N. tabacum Xanthi NN,N. glutinosa, N. glauca and N. rustica) suggesting that NH is a homologue of the N gene, rather than an allele. We have cloned and characterised the NH gene ( GenBank acc. no. bankit598573 AY535010) from nn susceptible plants and postulate that this gene might be involved in the HR-like response seen in these plants.
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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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    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.