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Author: search.filters.author.Ki, Seong KoHas files: Yes

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    LIMITED ADDITION OF THE 6-ARM Β1,2-LINKED N-ACETYLGLUCOSAMINE (GLCNAC) RESIDUE FACILITATES THE FORMATION OF THE LARGEST N-GLYCAN IN PLANTS
    (Pub Med, 2015-07-03) Jae, Yong Yoo; Ki, Seong Ko; Hyun-Kyeong, Seo; Seongha, Park; Wahyu, Indra Duwi Fanata; Rikno, Harmoko; Nirmal Kumar, Ramasamy; Thiyagarajan, Thulasinathan; Tesfaye, Mengiste; Jae-Min, Lim; Sang, Yeol Lee; Kyun, Oh Lee
    The most abundant N-glycan in plants is the paucimannosidic N-glycan with core β1,2-xylose and α1,3-fucose residues (Man3XylFuc(GlcNAc)2). Here, we report a mechanism in Arabidopsis thaliana that efficiently produces the largest N-glycan in plants. Genetic and biochemical evidence indicates that the addition of the 6-arm β1,2-GlcNAc residue by N-acetylglucosaminyltransferase II (GnTII) is less effective than additions of the core β1,2-xylose and α1,3-fucose residues by XylT, FucTA, and FucTB in Arabidopsis. Furthermore, analysis of gnt2 mutant and 35S:GnTII transgenic plants shows that the addition of the 6-arm non-reducing GlcNAc residue to the common N-glycan acceptor GlcNAcMan3(GlcNAc)2 inhibits additions of the core β1,2-xylose and α1,3-fucose residues. Our findings indicate that plants limit the rate of the addition of the 6-arm GlcNAc residue to the common N-glycan acceptor as a mechanism to facilitate formation of the prevalent N-glycans with Man3XylFuc(GlcNAc)2 and (GlcNAc)2Man3XylFuc(GlcNAc)2 structures.
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    N-GLYCAN MATURATION IS CRUCIAL FOR CYTOKININ-MEDIATED DEVELOPMENT AND CELLULOSE SYNTHESIS IN ORYZA SATIVA
    (Pub Med, 2013-02-25) Wahyu Indra, Duwi Fanata; Kyoung, Hwan Lee; Bo Hwa, Son; Jae, Yong Yoo; Rikno Harmoko, Harmoko; Ki, Seong Ko; Nirmal Kumar, Ramasamy; Kyung, Hwa Kim; Doo-Byoung, Oh; Hyun, Suk Jung; Jae-Yean, Kim; Sang, Yeol Lee; Kyun, Oh Lee
    To explore the physiological significance of N-glycan maturation in the plant Golgi apparatus, gnt1, a mutant with loss of N-acetylglucosaminyltransferase I (GnTI) function, was isolated in Oryza sativa. gnt1 exhibited complete inhibition of N-glycan maturation and accumulated high-mannose N-glycans. Phenotypic analyses revealed that gnt1 shows defective post-seedling development and incomplete cell wall biosynthesis, leading to symptoms such as failure in tiller formation, brittle leaves, reduced cell wall thickness, and decreased cellulose content. The developmental defects of gnt1 ultimately resulted in early lethality without transition to the reproductive stage. However, callus induced from gnt1 seeds could be maintained for periods, although it exhibited a low proliferation rate, small size, and hypersensitivity to salt stress. Shoot regeneration and dark-induced leaf senescence assays indicated that the loss of GnTI function results in reduced sensitivity to cytokinin in rice. Reduced expression of A-type O. sativa response regulators that are rapidly induced by cytokinins in gnt1 confirmed that cytokinin signaling is impaired in the mutant. These results strongly support the proposed involvement of N-glycan maturation in transport as well as in the function of membrane proteins that are synthesized via the endomembrane system.