Coniferin β-glucosidase is ionically bound to cell wall in differentiating xylem of poplar

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Lignin is crucial for the growth and persistence of vascular plants in diverse environments. Although biosynthesis and polymerization of lignin precursors have been subjected to in-depth studies, only limited information exists on the ways in which these precursors are transported. Recent research has demonstrated that V-ATPase-dependent transport of coniferyl alcohol glucoside (coniferin) is a major metabolic function in differentiating xylem of both angiosperms and gymnosperms. Localization of β-glucosidase involved in the cleavage of coniferin to coniferyl alcohol and glucose is important to clarify the role of coniferin in lignification; nevertheless, only little has been reported in angiosperms. Here, we demonstrated the presence of coniferin β-glucosidase activity in a cell wall ionically bound protein fraction extracted from differentiating xylem of poplar. Coniferin β-glucosidase localization is very likely in cell wall similar to previous reports in conifers. We identified a putative poplar coniferin β-glucosidase through phylogenetic analysis and named this protein “PtrBGL6”. Immunoprecipitation assays showed that the anti-PtrBGL6 antibody recognizes a coniferin β-glucosidase in a cell wall ionically bound protein fraction. Conserved coniferin β-glucosidases localized in cell wall in both angiosperm and gymnosperm implies their important roles in the formation of lignified cell wall.