			Home About us Contact

Mutant Seedlings (mutant + seedling)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Arabidopsis peroxisomal malate dehydrogenase functions in ,-oxidation but not in the glyoxylate cycle

THE PLANT JOURNAL, Issue 3 2007
Itsara Pracharoenwattana
Summary The aim was to determine the function of peroxisomal NAD+ -malate dehydrogenase (PMDH) in fatty acid ,-oxidation and the glyoxylate cycle in Arabidopsis. Seeds in which both PMDH genes are disrupted by T-DNA insertions germinate, but seedling establishment is dependent on exogenous sugar. Mutant seedlings mobilize their triacylglycerol very slowly and growth is insensitive to 2,4-dichlorophenoxybutyric acid. Thus mutant seedlings are severely impaired in ,-oxidation, even though microarray analysis shows that ,-oxidation genes are expressed normally. The mutant phenotype was complemented by expression of a cDNA encoding PMDH with either its native peroxisome targeting signal-2 (PTS2) targeting sequence or a heterologous PTS1 sequence. In contrast to the block in ,-oxidation in mutant seedlings, [14C]acetate is readily metabolized into sugars and organic acids, thereby demonstrating normal activity of the glyoxylate cycle. We conclude that PMDH serves to reoxidize NADH produced from fatty acid ,-oxidation and does not participate directly in the glyoxylate cycle. [source]

OsNOA1/RIF1 is a functional homolog of AtNOA1/RIF1: implication for a highly conserved plant cGTPase essential for chloroplast function

NEW PHYTOLOGIST, Issue 1 2010
Hongjia Liu
Summary ,The bacterial protein YqeH is a circularly permuted GTPase with homologs encoded by plant nuclear genomes. The rice homolog OsNOA1/RIF1 is encoded by the single-copy gene Os02g01440. OsNOA1/RIF1 is expressed in different tissues and is light-inducible. The OsNOA1/RIF1-EYFP fusion protein was targeted to chloroplasts in transgenic Arabidopsis plants. In addition, the rice homolog was able to rescue most of the growth phenotypes in an Arabidopsis rif1 mutant. ,Rice (Oryza sativa) OsNOA1/RIF1 RNAi mutant seedlings were chlorotic with reduced pigment contents and lower photosystem II (PSII) efficiency. However, the expressions of the chloroplast-encoded genes rbcL, atpB, psaA and psbA were not affected. By contrast, reduced abundance of the chloroplast 16S rRNA was observed in the mutant. ,Quantitative iTRAQ-LC-MS/MS proteomics investigations revealed proteome changes in the rice mutant consistent with the expected functional role of OsNOA1/RIF1 in chloroplast translation. The RNAi mutant showed significantly decreased expression levels of chloroplast-encoded proteins as well as nuclear-encoded components of chloroplast enzyme complexes. Conversely, upregulation of some classes of nonchloroplastic proteins, such as glycolytic and phenylpropanoid pathway enzymes, was detected. ,Our work provides independent indications that a highly conserved nuclear-encoded cGTPase of likely prokaryotic origin is essential for proper chloroplast ribosome assembly and/or translation in plants. [source]

Arabidopsis XXT5 gene encodes a putative ,-1,6-xylosyltransferase that is involved in xyloglucan biosynthesis

THE PLANT JOURNAL, Issue 1 2008
Olga A. Zabotina
Summary The function of a putative xyloglucan xylosyltransferase from Arabidopsis thaliana (At1g74380; XXT5) was studied. The XXT5 gene is expressed in all plant tissues, with higher levels of expression in roots, stems and cauline leaves. A T-DNA insertion in the XXT5 gene generates a readily visible root hair phenotype (root hairs are shorter and form bubble-like extrusions at the tip), and also causes the alteration of the main root cellular morphology. Biochemical characterization of cell wall polysaccharides isolated from xxt5 mutant seedlings demonstrated decreased xyloglucan quantity and reduced glucan backbone substitution with xylosyl residues. Immunohistochemical analyses of xxt5 plants revealed a selective decrease in some xyloglucan epitopes, whereas the distribution patterns of epitopes characteristic for other cell wall polysaccharides remained undisturbed. Transformation of xxt5 plants with a 35S::HA-XXT5 construct resulted in complementation of the morphological, biochemical and immunological phenotypes, restoring xyloglucan content and composition to wild-type levels. These data provide evidence that XXT5 is a xyloglucan ,-1,6-xylosyltransferase, and functions in the biosynthesis of xyloglucan. [source]

26S proteasome regulatory particle mutants have increased oxidative stress tolerance

THE PLANT JOURNAL, Issue 1 2008
Jasmina Kurepa
Summary The 26S proteasome (26SP) is a multi-subunit, multi-catalytic protease that is responsible for most of the cytosolic and nuclear protein turnover. The 26SP is composed of two sub-particles, the 19S regulatory particle (RP) that binds and unfolds protein targets, and the 20S core particle (20SP) that degrades proteins into small peptides. Most 26SP targets are conjugated to a poly-ubiquitin (Ub) chain that serves as a degradation signal. However, some targets, such as oxidized proteins, do not require a poly-Ub tag for proteasomal degradation, and recent studies have shown that the main protease in this Ub-independent pathway is free 20SP. It is currently unknown how the ratio of 26SP- to 20SP-dependent proteolysis is controlled. Here we show that loss of function of the Arabidopsis RP subunits RPT2a, RPN10 and RPN12a leads to decreased 26SP accumulation, resulting in reduced rates of Ub-dependent proteolysis. In contrast, all three RP mutants have increased 20SP levels and thus enhanced Ub-independent protein degradation. As a consequence of this shift in proteolytic activity, mutant seedlings are hypersensitive to stresses that cause protein misfolding, and have increased tolerance to treatments that promote protein oxidation. Taken together, the data show that plant cells increase 20SP-dependent proteolysis when 26SP activity is impaired. [source]

Arabidopsis peroxisomal malate dehydrogenase functions in ,-oxidation but not in the glyoxylate cycle

A role for caleosin in degradation of oil-body storage lipid during seed germination

THE PLANT JOURNAL, Issue 6 2006
Marianne Poxleitner
Summary Caleosin is a Ca2+ -binding oil-body surface protein. To assess its role in the degradation of oil-bodies, two independent insertion mutants lacking caleosin were studied. Both mutants demonstrated significant delay of breakdown of the 20:1 storage lipid at 48 and 60 h of germination. Additionally, although germination rates for seeds were not affected by the mutations, mutant seedlings grew more slowly than wild type when measured at 48 h of germination, a defect that was corrected with continued growth for 72 and 96 h in the light. After 48 h of germination, wild-type central vacuoles had smooth contours and demonstrated internalization of oil bodies and of membrane containing , - and , -tonoplast intrinsic proteins (TIPs), markers for protein storage vacuoles. In contrast, mutant central vacuoles had distorted limiting membranes displaying domains with clumps of the two TIPs, and they contained fewer oil bodies. Thus, during germination caleosin plays a role in the degradation of storage lipid in oil bodies. Its role involves both the normal modification of storage vacuole membrane and the interaction of oil bodies with vacuoles. The results indicate that interaction of oil bodies with vacuoles is one mechanism that contributes to the degradation of storage lipid. [source]

The maize viviparous15 locus encodes the molybdopterin synthase small subunit

THE PLANT JOURNAL, Issue 2 2006
Masaharu Suzuki
Summary A new Zea mays viviparous seed mutant, viviparous15 (vp15), was isolated from the UniformMu transposon-tagging population. In addition to precocious germination, vp15 has an early seedling lethal phenotype. Biochemical analysis showed reduced activities of several enzymes that require molybdenum cofactor (MoCo) in vp15 mutant seedlings. Because MoCo is required for abscisic acid (ABA) biosynthesis, the viviparous phenotype is probably caused by ABA deficiency. We cloned the vp15 mutant using a novel high-throughput strategy for analysis of high-copy Mu lines: We used MuTAIL PCR to extract genomic sequences flanking the Mu transposons in the vp15 line. The Mu insertions specific to the vp15 line were identified by in silico subtraction using a database of MuTAIL sequences from 90 UniformMu lines. Annotation of the vp15 -specific sequences revealed a Mu insertion in a gene homologous to human MOCS2A, the small subunit of molybdopterin (MPT) synthase. Molecular analysis of two allelic mutations confirmed that Vp15 encodes a plant MPT synthase small subunit (ZmCNX7). Our results, and a related paper reporting the cloning of maize viviparous10, demonstrate robust cloning strategies based on MuTAIL-PCR. The Vp15/CNX7, together with other CNX genes, is expressed in both embryo and endosperm during seed maturation. Expression of Vp15 appears to be regulated independently of MoCo biosynthesis. Comparisons of Vp15 loci in genomes of three cereals and Arabidopsis thaliana identified a conserved sequence element in the 5, untranslated region as well as a micro-synteny among the cereals. [source]

ELF4 is a phytochrome-regulated component of a negative-feedback loop involving the central oscillator components CCA1 and LHY

THE PLANT JOURNAL, Issue 2 2005
Elise A. Kikis
Summary Evidence has been presented that a negative transcriptional feedback loop formed by the genes CIRCADIAN CLOCK ASSOCIATED (CCA1), LATE ELONGATED HYPOCOTYL (LHY) and TIMING OF CAB (TOC1) constitutes the core of the central oscillator of the circadian clock in Arabidopsis. Here we show that these genes are expressed at constant, basal levels in dark-grown seedlings. Transfer to constant red light (Rc) rapidly induces a biphasic pattern of CCA1 and LHY expression, and a reciprocal TOC1 expression pattern over the first 24 h, consistent with initial induction of this synchronous oscillation by the light signal. We have used this assay with wild-type and mutant seedlings to examine the role of these oscillator components, and to determine the function of ELF3 and ELF4 in their light-regulated expression. The data show that whereas TOC1 is necessary for light-induced CCA1/LHY expression, the combined absence of CCA1 and LHY has little effect on the pattern of light-induced TOC1 expression, indicating that the negative regulatory arm of the proposed oscillator is not fully functional during initial seedling de-etiolation. By contrast, ELF4 is necessary for light-induced expression of both CCA1 and LHY, and conversely, CCA1 and LHY act negatively on light-induced ELF4 expression. Together with the observation that the temporal light-induced expression profile of ELF4 is counter-phased to that of CCA1 and LHY and parallels that of TOC1, these data are consistent with a previously unrecognized negative-feedback loop formed by CCA1/LHY and ELF4 in a manner analogous to the proposed CCA1/LHY/TOC1 oscillator. ELF3 is also necessary for light-induced CCA1/LHY expression, but it is neither light-induced nor clock-regulated during de-etiolation. Taken together, the data suggest (a) that ELF3, ELF4, and TOC1 all function in the primary, phytochrome-mediated light-input pathway to the circadian oscillator in Arabidopsis; and (b) that this oscillator consists of two or more interlocking transcriptional feedback loops that may be differentially operative during initial light induction and under steady-state circadian conditions in entrained green plants. [source]