Mediates the transfer of glucuronic acid (GlcA) from UDP-GlcA to glycosyl inositol phosphorylceramides (GIPCs) (PubMed:25122154, PubMed:27643972). The formation of GIPCs sphingolipids is essential for pollen function, plant growth and defense (PubMed:25122154, PubMed:27643972). Required for global fitness (PubMed:27643972). glucuronate acceptor + UDP-alpha-D-glucuronate = acceptor beta-D-glucuronoside + H(+) + UDP a 1D-myo-inositol-1-phospho-N-[(R)-2-hydroxy-very-long-chain fatty acyl]-(R)-4-hydroxysphingoid base + UDP-alpha-D-glucuronate = an alpha-D-glucuronosyl-(1<->6)-1D-myo-inositol-1-phospho-N-[(R)-2-hydroxy-very-long-chain fatty acyl]-(R)-4-hydroxysphingoid base + H(+) + UDP Sphingolipid metabolism. Expressed in seedlings, roots, leaves, stems and siliques. Expressed throughout pollen development. Defect in transmission of mutated alleles through the male gametophyte (e.g. pollen) (PubMed:25122154). Pollen rescued mutants show severe dwarfism with reduced roots, compromised pollen tube guidance, and constitutive activation of salicyclic acid-mediated defense pathways. They have also an altered sphingolipidome with reduced glycosyl inositol phosphorylceramides (GIPCs), increased ceramides, and an increased incorporation of short-chain fatty acids and dihydroxylated bases into inositol phosphorylceramides and GIPCs (PubMed:27643972). Belongs to the glycosyltransferase 8 family. Glycogenin subfamily.