β1,3-galactosyltransferase on chromosome 6 is essential for the formation of Lewis a structure on N -glycan in Oryza sativa

β1,3-galactose is the component of outer-chain elongation of complex N -glycans that, together with α1,4-fucose, forms Lewis a structures in plants. Previous studies have revealed that N -glycan maturation is mediated by sequential attachment of β1,3-galactose and α1,4-fucose by individual β1,3-galactosyltransferase (GalT) and α1,4-fucosyltransferase (1,4-FucT), respectively. Although GalT from several species has been studied, little information about GalT from rice is available. I therefore characterized three GalT candidate genes on different chromosomes in Oryza sativa . Seeds of rice lines that had T-DNA insertions in regions corresponding to individual putative GalT genes were obtained from a Rice Functional Genomic Express Database and plants grown until maturity. Homozygotes were selected from the next generation by genotyping PCR, and used for callus induction. Callus extracts of two independent T-DNA mutant rice which have T-DNA insertions at the same gene on chromosome 6 but in different exons showed highly reduced band intensity on a western blots using an anti-Lewis a antibody. Cell extracts and cultured media from suspension culture of the one of these mutant rice were further analysed by N -glycan profiling using matrix-associated laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF). Identified N -glycan species containing β1,3-galactose from both cell extracts and cultured media of knock-out mutant were less than 0.5% of total N -glycans while that of WT cells were 9.8% and 49.1%, respectively. This suggests that GalT located on rice chromosome 6 plays a major role in N -glycan galactosylation, and mutations within it lead to blockage of Lewis a epitope formation.