Arabinogalactan glycosyltransferases target to a unique subcellular compartment that may function in unconventional secretion in plants

We report that fluorescently tagged arabinogalactan glycosyltransferases target not only the Golgi apparatus but also uncharacterized smaller compartments when transiently expressed in Nicotiana benthamiana. Approximately 80% of AtGALT31A [Arabidopsis thaliana galactosyltransferase from family 31 (At1g32930)] was found in the small compartments, of which, 45 and 40% of AtGALT29A [Arabidopsis thaliana galactosyltransferase from family 29 (At1g08280)] and AtGlcAT14A [Arabidopsis thaliana glucuronosyltransferase from family 14 (At5g39990)] colocalized with AtGALT31A, respectively; in contrast, N-glycosylation enzymes rarely colocalized (3-18%), implicating a role of the small compartments in a part of arabinogalactan (O-glycan) biosynthesis rather than N-glycan processing. The dual localization of AtGALT31A was also observed for fluorescently tagged AtGALT31A stably expressed in an Arabidopsis atgalt31a mutant background. Further, site-directed mutagenesis of a phosphorylation site of AtGALT29A (Y144) increased the frequency of the protein being targeted to the AtGALT31A-localized small compartments, suggesting a role of Y144 in subcellular targeting. The AtGALT31A localized to the small compartments were colocalized with neither SYP61 (syntaxin of plants 61), a marker for trans-Golgi network (TGN), nor FM4-64-stained endosomes. However, 41% colocalized with EXO70E2 (Arabidopsis thaliana exocyst protein Exo70 homolog 2), a marker for exocyst-positive organelles, and least affected by Brefeldin A and Wortmannin. Taken together, AtGALT31A localized to small compartments that are distinct from the Golgi apparatus, the SYP61-localized TGN, FM4-64-stained endosomes and Wortmannin-vacuolated prevacuolar compartments, but may be part of an unconventional protein secretory pathway represented by EXO70E2 in plants

Mutation of an Arabidopsis Golgi membrane protein ELMO1 reduces cell adhesion

Plant growth, morphogenesis and development involve cellular adhesion, a process dependent on the composition and structure of the extracellular matrix or cell wall. Pectin in the cell wall is thought to play an essential role in adhesion, and its modification and cleavage are suggested to be highly regulated so as to change adhesive properties. To increase our understanding of plant cell adhesion, a population of ethyl methanesulfonate-mutagenized Arabidopsis were screened for hypocotyl adhesion defects using the pectin binding dye Ruthenium Red that penetrates defective but not wild-type (WT) hypocotyl cell walls. Genomic sequencing was used to identify a mutant allele of ELMO1 which encodes a 20 kDa Golgi membrane protein that has no predicted enzymatic domains. ELMO1 colocalizes with several Golgi markers and elmo1-/- plants can be rescued by an ELMO1-GFP fusion. elmo1-/- exhibits reduced mannose content relative to WT but no other cell wall changes and can be rescued to WT phenotype by mutants in ESMERALDA1, which also suppresses other adhesion mutants. elmo1 describes a previously unidentified role for the ELMO1 protein in plant cell adhesion

Arabidopsis Phyllotaxis Is Controlled by the Methyl-Esterification Status of Cell-Wall Pectins

SummaryPlant organs are produced from meristems in a characteristic pattern. This pattern, referred to as phyllotaxis, is thought to be generated by local gradients of an information molecule, auxin [1–6]. Some studies propose a key role for the mechanical properties of the cell walls in the control of organ outgrowth [7–12]. A major cell-wall component is the linear α-1-4-linked D-GalAp pectic polysaccharide homogalacturonan (HG), which plays a key role in cell-to-cell cohesion [13, 14]. HG is deposited in the cell wall in a highly (70%–80%) methyl-esterified form and is subsequently de-methyl-esterified by pectin methyl-esterases (PME, EC 3.1.1.11). PME activity is itself regulated by endogenous PME inhibitor (PMEI) proteins [15]. PME action modulates cell-wall-matrix properties and plays a role in the control of cell growth [16–18]. Here, we show that the formation of flower primordia in the Arabidopsis shoot apical meristem is accompanied by the de-methyl-esterification of pectic polysaccharides in the cell walls. In addition, experimental perturbation of the methyl-esterification status of pectins within the meristem dramatically alters the phyllotactic pattern. These results demonstrate that regulated de-methyl-esterification of pectins is a key event in the outgrowth of primordia and possibly also in phyllotactic patterning

Cadmium Tissue Concentrations in Kidney, Liver and Muscle in Moose (Alces alces) From First Nations Communities in Northern Alberta

The consumption of traditional foods, including moose, is vitally important to Canada's indigenous communities for dietary, social, and cultural reasons. Cadmium is a key contaminant of concern in moose as it accumulates primarily the organs, with the kidney accumulating more than the liver. The objectives of this study were to identify relationships between cadmium concentrations in the kidney, liver and muscle tissue of moose, and to estimate benchmark consumption quantities that are associated with minimal health risk for three First Nation communities: the Chipewyan Prairie Déné First Nation, the Swan River First Nation and Cold Lake First Nations. Moose quality studies were conducted with the Chipewyan Prairie Déné First Nation in 2012, the Swan River First Nation in 2014 and the Cold Lake First Nations in 2016, all located in Alberta, Canada. The measured cadmium tissue concentrations from these studies were found to be comparable to those reported in the 2016 Alberta First Nations Food, Nutrition and Environment Study, and other North American studies. The results of our study suggest that linear relationships exist between cadmium concentrations in kidney and liver tissue, which can be used as a tool to predict organ concentrations in moose from northern Alberta. First Nations communities can use this information to predict cadmium tissue concentrations in both kidney and liver in the absence of actual, measured cadmium concentrations. Benchmark consumption quantities that are associated with minimal risk were estimated for the different tissue types

FTIR analysis of xylem vessel cell walls in twining stem of Dioscorea balcanica

Using stem cross sections of Dioscorea balcanica, as a model, we detected changes in anatomy and structural organization of xylem vessel cell walls (CWs) linked to stem twining in liana plants. UV microscopy, scanning electron microscopy and Fourier transform infrared (FTIR) microspectrometry were used. Different microfibrils orientation in vessel CWs of twisted compared to straight internodes, revealed by histological examination, coincide with the lower lignin content, the lower amount of xylan and cellulose, and the higher amount of xyloglucan, showed by FTIR. Xylem vessels resist high mechanical strain developed in twisted internodes by decreased CW rigidity (lower lignin content) and extensibility (higher xyloglucan content), and increased elasticity (lower xylan content)

Fabrication, characterization and photoelectrochemical behavior of Fe2TiO5 screen printed thick films

Pseudobrookite paste was composed of a mixture of starting nanopowders of hematite (α-Fe2O3) and anatase (TiO2) in the molar ratio 1:1.5, organic vehicle and glass frit. The paste was screen printed on on fluorine-doped tin oxide (FTO) glass substrate using screen printing technology. Structural, morphological and optical studies have been carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The photo-electrochemical performance of Fe2TiO5 screen printed thick film was examined under xenon lamp illumination in 1 M NaOH electrolyte

Xyloglucan Remodeling Defines Auxin-Dependent Differential Tissue Expansion in Plants

Size control is a fundamental question in biology, showing incremental complexity in plants, whose cells possess a rigid cell wall. The phytohormone auxin is a vital growth regulator with central importance for differential growth control. Our results indicate that auxin-reliant growth programs affect the molecular complexity of xyloglucans, the major type of cell wall hemicellulose in eudicots. Auxin-dependent induction and repression of growth coincide with reduced and enhanced molecular complexity of xyloglucans, respectively. In agreement with a proposed function in growth control, genetic interference with xyloglucan side decorations distinctly modulates auxin-dependent differential growth rates. Our work proposes that auxin-dependent growth programs have a spatially defined effect on xyloglucan's molecular structure, which in turn affects cell wall mechanics and specifies differential, gravitropic hypocotyl growth