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Jonathan Phillips

Publications and source records attributed to Jonathan Phillips.

8 recordsLinked to original sources
PubMed2006

Proteome analysis of leaves from the resurrection plant Boea hygrometrica in response to dehydration and rehydration.

Resurrection plants differ from other species in their unique ability to survive desiccation. In order to understand the mechanisms of desiccation tolerance, proteome studies were carried out using leaves of the resurrection plant Boea hygrometrica to reveal proteins that were differentially expressed in response to changes in relative water content. This opportunity was afforded by the rare ability of excised B. hygrometrica leaves to survive and resume metabolism following desiccation in a manner similar to intact plants. From a total of 223 proteins that were reproducibly detected and analyzed, 35% showed increased abundance in dehydrated leaves, 5% were induced in rehydrated leaves and 60% showed decreased or unchanged abundance in dehydrated and rehydrated leaves. Since the induction kinetics fall into clearly defined patterns, we suggest that programmed regulation of protein expression triggered by changes of water status. Fourteen dehydration responsive proteins were analyzed by mass spectrometry. Eight proteins were classified as playing a role in reactive oxygen species scavenging, photosynthesis and energy metabolism. In agreement with these findings, glutathione content and polyphenol oxidase activity were found to increase upon dehydration and rapid recovery of photosynthesis was observed.

Energy Metabolism↗
PubMed2006

Graphitic structures by design.

It is shown that self-supporting graphitic structures of specific shape can be grown in a variety of forms, from nanoscale to macroscale, on metal templates, in a fuel-rich mixture of ethylene and oxygen at temperatures between 750 and 900 K. The evidence presented suggests graphite can be grown in any shape created from catalytic metals (e.g., Ni) under the proper conditions of temperature and gas composition. Structures produced include macroscale bodies, centimeters in dimension, composed of micrometer-scale graphite elements such as graphite "foam" and regular graphite "lattices". Nanoscale hollow graphite spheres were also produced. The production rate in the apparatus employed was roughly shown to be 1 layer/s and was steady with time over several hours. The process of producing self-supporting bodies generally produces hollow graphite structures, as the underlying metal template must be removed by acid following the completion of graphite growth. The process is believed to be possible only in an environment, such as combustion, in which a high concentration of particular radical species is present in the vicinity of the template surface. The following process is postulated: (i) a single layer of graphite is formed from gas-phase radicals by the catalytic action of the metal template, (ii) additional graphite growth is "autocatalytic" and occurs via the decomposition of radicals on the surface and the incorporation of "free" carbon atoms, or other radical fragments, into "edge sites" on the graphite surface.

Journal Article↗
PubMed2006

A high throughput Agrobacterium tumefaciens-mediated transformation method for functional genomics of perennial ryegrass (Lolium perenne L.).

A robust and high throughput Agrobacterium genetic transformation procedure has been developed for perennial ryegrass (Lolium perenne L.). Embryogenic callus lines were selected and maintained as plants in vitro. Embryogenic calli derived from meristematic regions of the vegetative tillers were co-cultivated with Agrobacterium tumefaciens strain EHA101 carrying the plasmid pCAMBIA 1305.1 in the presence of acetosyringone for 3-4 days. The calli were grown under 94.8 and 151.6 microM hygromycin selection, respectively for two cycles of 2-weeks each, followed by transfer to regeneration medium with 47.4 microM hygromycin. Regenerated plants were rooted and successfully transferred to soil. The transgenic nature of the regenerated plants was confirmed by DNA gel blot analysis and gene expression demonstrated by GUS histochemical assay and/or reverse transcription PCR. After development of the transformation procedure, we used Agrobacterium strain EHA101 carrying a modified binary plasmid pMH bearing genes of interest. In the past 2 years, we have produced more than 1,000 plants with constructs encoding different genes of interest from perennial ryegrass.

Agrobacterium tumefaciens↗
PubMed2006

A homeodomain leucine zipper gene from Craterostigma plantagineum regulates abscisic acid responsive gene expression and physiological responses.

A subset of homeodomain leucine zipper proteins (HDZip) play a role in regulating adaptation responses including developmental adjustment to environmental cues in plants. Here we report the structural and functional characterisation of a dehydration responsive nuclear-targeted HDZip transcriptional regulator, CpHB-7. DNA-protein interaction studies suggest that CDeT6-19, a known ABA and dehydration responsive dehydrin gene, is a potential target gene of CpHB-7 in the desiccation-tolerant plant Craterostigma plantagineum. Transgenic plants that ectopically express CpHB-7 display reduced sensitivity towards ABA during seed germination and stomatal closure. Expression analysis reveals that genes with induced or repressed expression in CpHB-7 ectopic expression lines are either mostly repressed or induced by ABA, drought or salt treatment respectively, thus demonstrating that CpHB-7 modifies ABA-responsive gene expression as a negative regulator. CpHB-7 gene expression is also linked to early organ development, leading to the suggestion that CpHB-7 is functionally similar to the Arabidopsis transcription factor, ATHB-6.

Abscisic Acid↗
PubMed2004

Novel dual-bed reactors: utilization of hydrogen spillover in reactor design.

Hydrogen spillover over macroscopic distances was demonstrated and exploited in the design of two novel catalytic reactors for 1-butene isomerization. A dual-bed reactor containing separate zones of noble metal and bimetallic catalysts yielded activities up to 2.7 times greater than that of the noble metal alone. The noble metal catalyst contained palladium supported on graphitic carbon. The bimetallic catalyst contained a base metal, either iron or cobalt, and a lanthanide metal, either cerium or praseodymium, also supported on graphitic carbon. The bimetallic catalysts by themselves had no measurable activity at the current experimental conditions. Results from a dual-bed, dual-feed reactor using the same catalysts showed dramatic activity increases relative to controls. In this reactor, the hydrocarbon never contacted the noble metal catalyst, yet substantial hydrocarbon conversion was measured. No hydrocarbon conversion was detected when blank support replaced the bimetallic catalyst or when no material at all was placed above the noble metal catalyst. In both reactors, the activity increase was attributed to hydrogen spillover. That is, molecular hydrogen adsorbed and dissociated on the noble metal catalyst. The adsorbed atomic hydrogen was then transported via surface diffusion to the bimetallic catalyst, activating those sites. The results also demonstrated that a catalytic reaction may occur at distinctly different reactive sites and that catalysts may be selected to promote specific steps within the reaction.

Journal Article↗
PubMed2004

Recombinant viruses and early global HIV-1 epidemic.

Central Africa was the epicenter of the HIV type 1 (HIV-1) pandemic. Understanding the early epidemic in the Democratic Republic of the Congo, formerly Zaire, could provide insight into how HIV evolved and assist vaccine design and intervention efforts. Using enzyme immunosorbent assays, we tested 3,988 serum samples collected in Kinshasa in the mid-1980s and confirmed seroreactivity by Western blot. Polymerase chain reaction of gag p17, env C2V3C3, and/or gp41; DNA sequencing; and genetic analyses were performed. Gene regions representing all the HIV-1 group M clades and unclassifiable sequences were found. From two or three short gene regions, 37% of the strains represented recombinant viruses, multiple infections, or both, which suggests that if whole genome sequences were available, most of these strains would have mosaic genomes. We propose that the HIV epidemic was well established in central Africa by the early 1980s and that some recombinant viruses most likely seeded the early global epidemic.

Democratic Republic of the Congo↗
PubMed2002

Characterization of five novel dehydration-responsive homeodomain leucine zipper genes from the resurrection plant Craterostigma plantagineum.

Homeodomain leucine zipper (HDZip) genes encode putative transcription factors that are unique to plants. A function in regulating processes that are specific for plants is postulated, such as responses to environmental cues and developmental signals. This is supported by a growing body of evidence resulting from studies of HDZip genes in a variety of species. In addition to the previously isolated CPHB-1 and -2 genes, this paper reports the isolation of members of five families of Craterostigma plantagineum homeobox leucine zipper genes (CPHB) via a yeast one-hybrid screening approach. Based on the sequence homology and protein interactions the encoded proteins (CPHB-3/4/5/6/7) were classified into HDZip class II and I genes. Homo- and heterodimerization of CPHB proteins within the same structurally related class has been demonstrated and the DNA-binding activity of CPHB proteins to two homeodomain recognition elements (HDE1 and HDE2) has been compared in yeast. All families of CPHB genes were modulated in their expression in response to dehydration in leaves and roots. CPHB-6 and CPHB-7 transcripts accumulated in leaves during early stages of dehydration and decreased after prolonged dehydration. Both transcripts were also induced in ABA-treated callus. CPHB-3/4/5 were down-regulated by dehydration in both leaves and roots. The results support the role of HDZips in regulating programs of gene expression in C. plantagineum that lead to desiccation tolerance.

Abscisic Acid↗