α-Glucosidase I is required for cellulose biosynthesis and morphogenesis in Arabidopsis

Abstract

Novel mutations in the RSW1 and KNOPF genes were identified in a large-scale screen for mutations that affect cell expansion in early Arabidopsis embryos. Embryos from both types of mutants were radially swollen with greatly reduced levels of crystalline cellulose, the principal structural component of the cell wall. Because RSW1 was previously shown to encode a catalytic subunit of cellulose synthase, the similar morphology of knf and rsw1-2 embryos suggests that the radially swollen phenotype of knf mutants is largely due to their cellulose deficiency. Map-based cloning of the KNF gene and enzyme assays of knf embryos demonstrated that KNF encodes α-glucosidase I, the enzyme that catalyzes the first step in N-linked glycan processing. The strongly reduced cellulose content of knf mutants indicates that N-linked glycans are required for cellulose biosynthesis. Because cellulose synthase catalytic subunits do not appear to be N glycosylated, the N-glycan requirement apparently resides in other component(s) of the cellulose synthase machinery. Remarkably, cellular processes other than extracellular matrix biosynthesis and the formation of protein storage vacuoles appear unaffected in knf embryos. Thus in Arabidopsis cells, like yeast, N-glycan trimming is apparently required for the function of only a small subset of N-glycoproteins.

Glycosylphosphatidylinositol-Anchored Proteins Are Required for Cell Wall Synthesis and Morphogenesis in Arabidopsis

“…The gene name refers to the characteristic shape and wrinkled seed coat of mutant seeds. Mutant embryos exhibit a radially swollen phenotype that is similar to strong alleles of the cellulose-deficient rsw1 mutants (Beeckman et al, 2002;Gillmor et al, 2002), in that they show altered polarity of cell expansion in outer cell layers during embryogenesis (Figure 1).…”

“…Five pnt mutants were recovered by microscopic analysis of embryo and seed morphology (Gillmor et al, 2002). The gene name refers to the characteristic shape and wrinkled seed coat of mutant seeds.…”

“…The importance of N-glycosylation for cellulose biosynthesis has been demonstrated (Lukowitz et al, 2001;Burn et al, 2002;Gillmor et al, 2002). Another posttranslational modification of cell wall-localized proteins is the addition of a glycosylphosphatidylinositol (GPI) membrane anchor, which is synthesized by enzyme complexes associated with the ER membrane.…”

“…The mutants were recovered in a genetic screen for radially swollen embryos (Gillmor et al, 2002). PNT1 encodes a predicted mannosyltransferase with sequence similarity to human PIG-M, an ER-localized mannosyltransferase that is required for synthesis of the GPI anchor (Maeda et al, 2001).…”

α-Mannosidase Involved in Turnover of Plant Complex TypeN-Glycans in Tomato (Lycopersicum esculentum) Fruits

“…2,3) The former -mannosidases reside in the endoplasmic reticulum (ER) or Golgi apparatus and play a critical role in the early stage of processing pathway of N-glycans. 1) In plant cells, it has been found that N-glycan processing by -glucosidase I and II in the ER is critical to growth and development, [4][5][6] but N-glycan processing in Golgi apparatus appeared to have little effect on normal growth. Arabidopsis mutants that lack N-acetylglucosaminyltransferase I (GNT-I) 7) or bothxylosyltransferase ( 1-2XylT) and -fucosyltransferase ( 1-3FucT) 8) grow normally and produce normal seeds.…”