139 research outputs found
The CELLULOSE SYNTHASE-LIKE A and CELLULOSE SYNTHASE-LIKE C families: recent advances and future perspectives
The CELLULOSE SYNTHASE (CESA) superfamily of proteins contains several sub-families of closely related CELLULOSE SYNTHASE-LIKE (CSL) sequences. Among these, the CSLA and CSLC families are closely related to each other and are the most evolutionarily divergent from the CESA family. Significant progress has been made with the functional characterization of CSLA and CSLC genes, which have been shown to encode enzymes with 1,4-β-glycan synthase activities involved in the biosynthesis of mannan and possibly xyloglucan backbones, respectively. This review examines recent work on the CSLA and CSLC families from evolutionary, molecular, and biochemical perspectives. We pose a series of questions, whose answers likely will provide further insight about the specific functions of members of the CSLA and CSLC families and about plant polysaccharide biosynthesis is general
Subsonic Boundary-Layer Wavefront Spectra for a Range of Reynolds Numbers
Aero-optic measurements of turbulent boundary layers were performed in wind tunnels at the University of Notre Dame and California Institute of Technology for heated walls at a
range of Reynolds numbers. Temporally resolved measurements of wavefronts were collected at a range of Mach numbers between 0.03 and 0.4 and the range of Re_θ between
1,700 and 20,000. Wavefront spectra for both heated and un-heated walls were extracted and compared to demonstrate that wall heating does not noticeably alter the shape of
wavefront spectra in the boundary layer. The effect of Reynolds number on the normalized spectra was also presented, and an empirical spectral model was modified to account for Reynolds number dependence. Measurements of OPD_(rms) for heated walls were shown to be consistent with results from prior experiments, and a method of estimating OPD_(rms) and other boundary layer statistics from wavefront measurements of heated-wall boundary layers was demonstrated and discussed
Deep EST profiling of developing fenugreek endosperm to investigate galactomannan biosynthesis and its regulation
Galactomannans are hemicellulosic polysaccharides composed of a (1 → 4)-linked β-D-mannan backbone substituted with single-unit (1 → 6)-α-linked D-galactosyl residues. Developing fenugreek (Trigonella foenum-graecum) seeds are known to accumulate large quantities of galactomannans in the endosperm, and were thus used here as a model system to better understand galactomannan biosynthesis and its regulation. We first verified the specific deposition of galactomannans in developing endosperms and determined that active accumulation occurred from 25 to 38 days post anthesis (DPA) under our growth conditions. We then examined the expression levels during seed development of ManS and GMGT, two genes encoding backbone and side chain synthetic enzymes. Based on transcript accumulation dynamics for ManS and GMGT, cDNA libraries were constructed using RNA isolated from endosperms at four ages corresponding to before, at the beginning of, and during active galactomannan deposition. DNA from these libraries was sequenced using the 454 sequencing technology to yield a total of 1.5 million expressed sequence tags (ESTs). Through analysis of the EST profiling data, we identified genes known to be involved in galactomannan biosynthesis, as well as new genes that may be involved in this process, and proposed a model for the flow of carbon from sucrose to galactomannans. Measurement of in vitro ManS and GMGT activities and analysis of sugar phosphate and nucleotide sugar levels in the endosperms of developing fenugreek seeds provided data consistent with this model. In vitro enzymatic assays also revealed that the ManS enzyme from fenugreek endosperm preferentially used GDP-mannose as the substrate for the backbone synthesis
Analysis of alanine aminotransferase in various organs of soybean (Glycine max) and in dependence of different nitrogen fertilisers during hypoxic stress
Alanine aminotransferase (AlaAT) catalyses the reversible conversion of pyruvate and glutamate into alanine and oxoglutarate. In soybean, two subclasses were identified, each represented by two highly similar members. To investigate the role of AlaAT during hypoxic stress in soybean, changes in transcript level of both subclasses were analysed together with the enzyme activity and alanine content of the tissue. Moreover, the dependency of AlaAT activity and gene expression was investigated in relation to the source of nitrogen supplied to the plants. Using semi-quantitative PCR, GmAlaAT genes were determined to be highest expressed in roots and nodules. Under normal growth conditions, enzyme activity of AlaAT was detected in all organs tested, with lowest activity in the roots. Upon waterlogging-induced hypoxia, AlaAT activity increased strongly. Concomitantly, alanine accumulated. During re-oxygenation, AlaAT activity remained high, but the transcript level and the alanine content decreased. Our results show a role for AlaAT in the catabolism of alanine during the initial period of re-oxygenation following hypoxia. GmAlaAT also responded to nitrogen availability in the solution during waterlogging. Ammonium as nitrogen source induced both gene expression and enzyme activity of AlaAT more than when nitrate was supplied in the nutrient solution. The work presented here indicates that AlaAT might not only be important during hypoxia, but also during the recovery phase after waterlogging, when oxygen is available to the tissue again
Differential regulation of alanine aminotransferase homologues by abiotic stresses in wheat (Triticum aestivum L.) seedlings
Wheat (Triticum aestivum L.) seedlings contain four alanine aminotransferase (AlaAT) homologues. Two of them encode AlaAT enzymes, whereas two homologues act as glumate:glyoxylate aminotransferase (GGAT). To address the function of the distinct AlaAT homologues a comparative examination of the changes in transcript level together with the enzyme activity and alanine and glutamate content in wheat seedlings subjected to low oxygen availability, nitrogen and light deficiency has been studied. Shoots of wheat seedlings were more tolerant to hypoxia than the roots as judging on the basis of enzyme activity and transcript level. Hypoxia induced AlaAT1 earlier in roots than in shoots, while AlaAT2 and GGAT were unaffected. The increase in AlaAT activity lagged behind the increase in alanine content. Nitrogen deficiency has little effect on the activity of GGAT. In contrast, lower activity of AlaAT and the level of mRNA for AlaAT1 and AlaAT2 in wheat seedlings growing on a nitrogen-free medium seems to indicate that AlaAT is regulated by the availability of nitrogen. Both AlaAT and GGAT activities were present in etiolated wheat seedlings but their activity was half of that observed in light-grown seedlings. Exposure of etiolated seedlings to light caused an increase in enzyme activities and up-regulated GGAT1. It is proposed that hypoxia-induced AlaAT1 and light-induced peroxisomal GGAT1 appears to be crucial for the regulation of energy availability in plants grown under unfavourable environmental conditions
The Glycosyltransferase Repertoire of the Spikemoss Selaginella moellendorffii and a Comparative Study of Its Cell Wall
Spike mosses are among the most basal vascular plants, and one species, Selaginella moellendorffii, was recently selected for full genome sequencing by the Joint Genome Institute (JGI). Glycosyltransferases (GTs) are involved in many aspects of a plant life, including cell wall biosynthesis, protein glycosylation, primary and secondary metabolism. Here, we present a comparative study of the S. moellendorffii genome across 92 GT families and an additional family (DUF266) likely to include GTs. The study encompasses the moss Physcomitrella patens, a non-vascular land plant, while rice and Arabidopsis represent commelinid and non-commelinid seed plants. Analysis of the subset of GT-families particularly relevant to cell wall polysaccharide biosynthesis was complemented by a detailed analysis of S. moellendorffii cell walls. The S. moellendorffii cell wall contains many of the same components as seed plant cell walls, but appears to differ somewhat in its detailed architecture. The S. moellendorffii genome encodes fewer GTs (287 GTs including DUF266s) than the reference genomes. In a few families, notably GT51 and GT78, S. moellendorffii GTs have no higher plant orthologs, but in most families S. moellendorffii GTs have clear orthologies with Arabidopsis and rice. A gene naming convention of GTs is proposed which takes orthologies and GT-family membership into account. The evolutionary significance of apparently modern and ancient traits in S. moellendorffii is discussed, as is its use as a reference organism for functional annotation of GTs
Evaluation of the significance of cell wall polymers in flax infected with a pathogenic strain of Fusarium oxysporum
Role of plant glyoxylate reductases during stress: a hypothesis
Molecular modelling suggests that a group of proteins in plants known as the β-hydroxyacid dehydrogenases, or the hydroxyisobutyrate dehydrogenase superfamily, includes enzymes that reduce succinic semialdehyde and glyoxylate to γ-hydroxybutyrate and glycolate respectively. Recent biochemical and expression studies reveal that NADPH-dependent cytosolic (termed GLYR1) and plastidial (termed GLYR2) isoforms of succinic semialdehyde/glyoxylate reductase exist in Arabidopsis. Succinic semialdehyde and glyoxylate are typically generated in leaves via two distinct metabolic pathways, γ-aminobutyrate and glycolate respectively. In the present review, it is proposed that the GLYRs function in the detoxification of both aldehydes during stress and contribute to redox balance. Outstanding questions are highlighted in a scheme for the subcellular organization of the detoxification mechanism in Arabidopsis
Refinement of Light-Responsive Transcript Lists Using Rice Oligonucleotide Arrays: Evaluation of Gene-Redundancy
Studies of gene function are often hampered by gene-redundancy, especially in organisms with large genomes such as rice (Oryza sativa). We present an approach for using transcriptomics data to focus functional studies and address redundancy. To this end, we have constructed and validated an inexpensive and publicly available rice oligonucleotide near-whole genome array, called the rice NSF45K array. We generated expression profiles for light- vs. dark-grown rice leaf tissue and validated the biological significance of the data by analyzing sources of variation and confirming expression trends with reverse transcription polymerase chain reaction. We examined trends in the data by evaluating enrichment of gene ontology terms at multiple false discovery rate thresholds. To compare data generated with the NSF45K array with published results, we developed publicly available, web-based tools (www.ricearray.org). The Oligo and EST Anatomy Viewer enables visualization of EST-based expression profiling data for all genes on the array. The Rice Multi-platform Microarray Search Tool facilitates comparison of gene expression profiles across multiple rice microarray platforms. Finally, we incorporated gene expression and biochemical pathway data to reduce the number of candidate gene products putatively participating in the eight steps of the photorespiration pathway from 52 to 10, based on expression levels of putatively functionally redundant genes. We confirmed the efficacy of this method to cope with redundancy by correctly predicting participation in photorespiration of a gene with five paralogs. Applying these methods will accelerate rice functional genomics
Altered ABA, proline and hydrogen peroxide in an Arabidopsis glutamate:glyoxylate aminotransferase mutant
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