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ABSTRACT: Determination of the role of mitochondrial (mt) ATP synthesis in plant metabolism is complicated by chloroplastic ATP synthesis. To differentiate ATP synthesis from these two organelles, we created transgenic Arabidopsis plants in which two different subunits of the mt ATP synthase, the oligomycin sensitivity-conferring protein (OSCP) (=delta) (ATP5) and the gamma (ATP3) subunit, were expressed individually in antisense orientation under the control of a dexamethasone-inducible promoter. The phenotypic effects of antisense expression were identical for both atp5 and atp3. Seedling lethality resulted from induction during germination in the light, demonstrating the essentiality of both gene products. Reduced expression of either gene resulted in stunting of dark-grown (etiolated) seedlings, downward curling or wavy-edged leaf margins of light-grown plants and ball-shaped unexpanded flowers. Antisense induction reduced total ATP levels in dark-grown (etiolated) seedlings germinated on media lacking sucrose, but increased total ATP levels in induced light-grown plants and in induced dark-grown seedlings germinated on media containing sucrose. Induction reduced transcript levels for two transcription factors (TCP3 and TCP4) whose decreased expression is associated with a similar wavy-edged leaf phenotype in Arabidopsis, and increased transcript levels for dynamin-related proteins whose increased expression is associated with increased mt division. Reduced expression of these subunits of the mt ATP synthase is proposed to disturb cellular redox states, which ultimately manifest downstream as diverse and seemingly unrelated phenotypes.
Plant and Cell Physiology 09/2009; 50(10):1840-50. · 4.70 Impact Factor
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ABSTRACT: Plant growth-promoting rhizobacteria (PGPR) can have positive effects on vigour and productivity, especially under stress conditions. In asparagus (Asparagus officinalis L.) field culture, seeds are planted in high-density nurseries, and 1-year-old crowns are transplanted to production fields. Performance can be negatively affected by water stress, transplant shock, and disease pressure on wounded roots. PGPR inoculation has the potential to alleviate some of the stresses incurred in the production system. In this study, the effects of PGPR (Pseudomonas spp.) treatment were determined on 3-week-old greenhouse-grown seedlings and germinating seeds of 2 asparagus cultivars. The pots were irrigated to a predetermined level that resulted in optimum growth or the plants were subjected to drought or flooding stress for 8 weeks. The cultivars responded differently to PGPR: single inoculations of seedlings enhanced growth of 'Guelph Millennium' under optimum conditions and 'Jersey Giant' seedlings under drought stress. Seed inoculations with PGPR resulted in a positive response only for 'Guelph Millennium', for which both single or multiple inoculations enhanced plant growth under drought stress.
Canadian Journal of Microbiology 05/2009; 55(4):388-94. · 1.36 Impact Factor
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ABSTRACT: Two different atp8 reading frames with divergent C-terminal extensions were identified in a sterility-inducing mitochondrial type (mitotype) of carrot; examination of three fertility-inducing mitotypes revealed atp8 reading frames that were either terminated at a position conserved among other plant atp8 genes or continued with unique C-terminal extensions. Similarities between the C-terminal extensions suggest ancient common ancestry, but the level of sequence divergence implies lack of functional conservation. Northern analysis indicated that the C-terminal extensions are transcribed and are present within the primary atp8 transcripts. Western analysis revealed that the products of the two extended atp8 reading frames encoded by the sterility-inducing mitotype are significantly smaller than those predicted by complete translation of their C-terminal extensions, but are slightly larger than the products from unextended reading frames. No alterations were observed in atp8 transcripts or proteins isolated from flowers of the sterility-inducing mitotype that were phenotypically fertile as a result of segregation for nuclear fertility-restoring Ms or Rf alleles, and thus, there is no evidence that expression of atp8 is directly involved in the petaloid cms phenotype in carrot.
Theoretical and Applied Genetics 06/2006; 112(8):1496-502. · 3.30 Impact Factor
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ABSTRACT: An inverted repeat in the mitochondrial DNA of carrot mitochondrial type (mitotype) SW3 has been sequenced in the context of its up- and downstream genomic environments. The 3,159 bp repeat encodes rps7 and cox1, but the cox1 reading frame does not encode a stop codon at a position predicted by alignment with other plant cox1 genes; cox1 extends into both of the downstream flanking sequences as unique C-terminal extensions of 224 (cox1-1) or 284 (cox1-2) amino acids. Northern and RT-PCR analyses revealed that rps7 and cox1 are co-transcribed and RNA-edited. In three additional mitotypes of carrot, rps7 and cox1 are co-transcribed, but are present as single copies within the genome. In mitotype FG17, the cox1 gene has a C-terminal extension like cox1-1, but in mitotypes FW2 and FW4, the cox1 genes lack C-terminal extensions and have stop codons and 3' UTRs like those of other plant cox1 genes. The C-terminal extensions are transcribed in SW3 and FG17 and result in longer primary transcripts than those from FW2 and FW4. Western immunoblotting of mitochondrial proteins from all mitotypes detected COX1 products of the predicted unextended size in all mitotypes, irrespective of the presence of a C-terminal extension in the reading frame.
Molecular and General Genetics 02/2006; 275(1):68-73. · 2.63 Impact Factor
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ABSTRACT: The mitochondrial genome of mitochondrial type (mitotype) SW3 of carrot (Daucus carota L.) encodes intact reading frames for a RNA polymerase (Rpo) and a DNA polymerase (Dpo) similar to those encoded by linear mitochondrial plasmids from plants. A BLAST search of translated nucleotide sequences in GenBank revealed previously unreported plasmid-like Rpo or Dpo sequence fragments in many plant mitochondrial DNAs. Phylogenetic analyses of the relationships between mitochondrial (mt)DNA-encoded and plasmid-encoded Rpos and Dpos from plants suggest that the mitochondrial sequences were derived from integrated plant plasmid sequences. A linear mitochondrial plasmid was detected in a different mitotype (FG21) of carrot by Southern hybridization of the Rpo and Dpo to undigested mtDNAs. Transcripts of the mtDNA-encoded Rpo and Dpo in mitotype SW3 were detected by RT-PCR.
Current Genetics 02/2005; 47(1):57-66. · 2.56 Impact Factor
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ABSTRACT: Genetic analysis of natural variation in ecotypes of Arabidopsis thaliana can facilitate the discovery of new genes or of allelic variants of previously identified genes controlling physiological processes in plants. We mapped quantitative trait loci (QTL) for light response in recombinant inbred lines (RILs) derived from the Columbia and Kashmir accessions via two methods: composite interval mapping and eXtreme array mapping (XAM). After measuring seedling hypocotyl lengths in blue, red, far-red, and white light, and in darkness, eight QTL were identified by composite interval mapping and five localized near photoreceptor loci. Two QTL in blue light were associated with CRY1 and CRY2, two in red light were near PHYB and PHYC, and one in far-red light localized near PHYA. The RED2 and RED5 QTL were verified in segregating lines. XAM was tested for the identification of QTL in red light with pools of RILs selected for extreme phenotypes. Thousands of single feature polymorphisms detected by differential DNA hybridized to high-density oligo-nucleotide arrays were used to estimate allele frequency differences between the pools. The RED2 QTL was identified clearly; differences exceeded a threshold of significance determined by simulations. The sensitivities of XAM to population type and size and genetic models were also determined by simulation analysis.
Genetics 07/2004; 167(2):907-17. · 4.01 Impact Factor
