Suppression of Arabidopsis GGLT1 affects growth by reducing the L-galactose content and borate cross-linking of rhamnogalacturonan-II.

Boron is a micronutrient that is required for the normal growth and development of vascular plants, but its precise functions remain a subject of debate. One established role for boron is in the cell wall where it forms a diester cross-link between two monomers of the low-abundance pectic polysaccharide rhamnogalacturonan-II (RG-II). The inability of RG-II to properly assemble into a dimer results in the formation of cell walls with abnormal biochemical and biomechanical properties and has a severe impact on plant productivity. Here we describe the effects on RG-II structure and cross-linking and on the growth of plants in which the expression of a GDP-sugar transporter (GONST3/GGLT1) has been reduced. In the GGLT1-silenced plants the amount of L-galactose in side-chain A of RG-II is reduced by up to 50%. This leads to a reduction in the extent of RG-II cross-linking in the cell walls as well as a reduction in the stability of the dimer in the presence of calcium chelators. The silenced plants have a dwarf phenotype, which is rescued by growth in the presence of increased amounts of boric acid. Similar to the mur1 mutant, which also disrupts RG-II cross-linking, GGLT1-silenced plants display a loss of cell wall integrity under salt stress. We conclude that GGLT1 is probably the primary Golgi GDP-L-galactose transporter, and provides GDP-L-galactose for RG-II biosynthesis. We propose that the L-galactose residue is critical for RG-II dimerization and for the stability of the borate cross-link.

Inter-α inhibitor proteins maintain neutrophils in a resting state by regulating shape and reducing ROS production.

The plasma levels of inter-α inhibitor proteins (IAIPs) are decreased in patients with sepsis and the reduced levels correlate with increased mortality. In the present study, we examined the effects of IAIPs on human neutrophils to better understand the beneficial effects of IAIPs in the treatment of sepsis. We demonstrated that IAIPs induced a spherical shape that was smaller in size with a smooth cellular surface in a concentration-dependent manner. These changes were inhibited by a specific antibody against IAIPs. In contrast, bikunin, light chain of IAIP, had no effect on neutrophil morphology. The neutrophils treated with IAIPs could easily pass through the artificial microcapillaries and were prevented from entrapment inside the capillaries. Coincubation of human blood neutrophils with a confluent human vascular endothelial monolayer showed that adhesion of neutrophils on endothelial cells was suppressed by treatment with IAIPs. IAIPs inhibited the spontaneous release of reactive oxygen species (ROS) in a concentration-dependent fashion. ROS inhibition was associated with reductions in p47phox phosphorylation on Ser328. These results suggest that IAIP-induced morphological changes that render neutrophils quiescent, facilitate passage through the microvasculature, and reduce adhesion to vascular endothelial cells and production of ROS. Thus, IAIP plays a key role in controlling neutrophil activation.