Transphosphatidylation by GIPC-PLD

Glycosylinositol phosphoceramide (GIPC) is the most abundant sphingolipid in plants and fungi. Recently, we detected GIPC-specific phospholipase D (GIPC-PLD) activity in plants. Here, we found that GIPC-PLD activity in young cabbage leaves catalyzes transphosphatidylation. The available alcohol for this reaction is a primary alcohol with a chain length below C4. Neither secondary alcohol, tertiary alcohol, choline, serine nor glycerol serves as an acceptor for transphosphatidylation of GIPC-PLD. We also found that cabbage GIPC-PLD prefers GIPC containing two sugars. Neither inositol phosphoceramide, mannosylinositol phosphoceramide nor GIPC with three sugar chains served as substrate. GIPC-PLD will become a useful catalyst for modification of polar head group of sphingophospholipid

The Arabidopsis thaliana nucleotide sugar transporter GONST2 is a functional homolog of GONST1.

Glycosylinositolphosphorylceramides (GIPCs) are the predominant lipid in the outer leaflet of the plasma membrane. Characterized GIPC glycosylation mutants have severe or lethal plant phenotypes. However, the function of the glycosylation is unclear. Previously, we characterized Arabidopsis thaliana GONST1 and showed that it was a nucleotide sugar transporter which provides GDP-mannose for GIPC glycosylation. gonst1 has a severe growth phenotype, as well as a constitutive defense response. Here, we characterize a mutant in GONST1's closest homolog, GONST2. The gonst2-1 allele has a minor change to GIPC headgroup glycosylation. Like other reported GIPC glycosylation mutants, gonst1-1gonst2-1 has reduced cellulose, a cell wall polymer that is synthesized at the plasma membrane. The gonst2-1 allele has increased resistance to a biotrophic pathogen Golovinomyces orontii but not the necrotrophic pathogen Botrytis cinerea. Expression of GONST2 under the GONST1 promoter can rescue the gonst1 phenotype, indicating that GONST2 has a similar function to GONST1 in providing GDP-D-Man for GIPC mannosylation

Loss of Inositol Phosphorylceramide Sphingolipid Mannosylation Induces Plant Immune Responses and Reduces Cellulose Content in Arabidopsis

Glycosylinositol phosphorylceramides (GIPCs) are a class of glycosylated sphingolipids found in plants, fungi, and protozoa. These lipids are abundant in the plant plasma membrane, forming ∼25% of total plasma membrane lipids. Little is known about the function of the glycosylated headgroup, but two recent studies have indicated that they play a key role in plant signaling and defense. Here, we show that a member of glycosyltransferase family 64, previously named ECTOPICALLY PARTING CELLS1, is likely a Golgi-localized GIPC-specific mannosyl-transferase, which we renamed GIPC MANNOSYL-TRANSFERASE1 (GMT1). Sphingolipid analysis revealed that the Arabidopsis thaliana gmt1 mutant almost completely lacks mannose-carrying GIPCs. Heterologous expression of GMT1 in Saccharomyces cerevisiae and tobacco (Nicotiana tabacum) cv Bright Yellow 2 resulted in the production of non-native mannosylated GIPCs. gmt1 displays a severe dwarfed phenotype and a constitutive hypersensitive response characterized by elevated salicylic acid and hydrogen peroxide levels, similar to that we previously reported for the Golgi-localized, GIPC-specific, GDP-Man transporter GONST1 (Mortimer et al., 2013). Unexpectedly, we show that gmt1 cell walls have a reduction in cellulose content, although other matrix polysaccharides are unchanged

The ASTRO-H X-ray Observatory

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the high-energy universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV. These instruments include a high-resolution, high-throughput spectrometer sensitive over 0.3-2 keV with high spectral resolution of Delta E < 7 eV, enabled by a micro-calorimeter array located in the focal plane of thin-foil X-ray optics; hard X-ray imaging spectrometers covering 5-80 keV, located in the focal plane of multilayer-coated, focusing hard X-ray mirrors; a wide-field imaging spectrometer sensitive over 0.4-12 keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope; and a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the 40-600 keV band. The simultaneous broad bandpass, coupled with high spectral resolution, will enable the pursuit of a wide variety of important science themes.Comment: 22 pages, 17 figures, Proceedings of the SPIE Astronomical Instrumentation "Space Telescopes and Instrumentation 2012: Ultraviolet to Gamma Ray

Hitomi (ASTRO-H) X-ray Astronomy Satellite

The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E  >  2  keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month

Dissection of Arabidopsis Bax Inhibitor-1 Suppressing Bax–, Hydrogen Peroxide–, and Salicylic Acid–Induced Cell Death

Overexpression of plant Bax Inhibitor-1 (BI-1) was able to suppress Bax-mediated cell death in yeast and Arabidopsis. Here, we demonstrate that reactive oxygen species production induced by the ectopic expression of Bax was insensitive to the coexpression of AtBI-1. Similarly, H(2)O(2)– or salicylic acid–mediated cell death also was suppressed in tobacco BY-2 cells overexpressing AtBI-1. To define the functional domain of AtBI-1 as a cell death suppressor, a truncated series of the AtBI-1 protein was analyzed in yeast possessing a galactose-inducible mammalian Bax. The results showed that ΔC-AtBI-1 (with the C-terminal 14 amino acids deleted) lost the ability to sustain cell growth. Furthermore, a mutant protein in which the C-terminal seven amino acid residues of AtBI-1 were replaced with others lacking a coiled-coil structure failed to inhibit cell death, suggesting that the C-terminal region is essential for the inhibition of cell death. We also noted that the C-terminal hydrophilic region was interchangeable between animal and plant Bax inhibitors

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Not AvailableThroughout the life cycle of plants, programmed cell death (PCD) is involved in a wide range of developmental processes and responses against abiotic or biotic stresses. PCD is an active form of cellular suicide controlled by a network of genes. Such phenomenon is associated with recovery of cellular compounds and sustaining plant life. Basic morphological and biochemical features of PCD are believed to be conserved in both plants and animals. Nevertheless, recent studies demonstrate an involvement of organelles such as vacuole and chloroplast in plant cell death regulation, indicating that plants evolved own cell death machinery. Reactive oxygen species (ROS) generated by biotic and abiotic stresses act as a signal that induces plant PCD. This article describes some of the fundamental characteristics of plant PCD and raises points that may lead to a better understanding and novel strategies for plant molecular breedingNot Availabl