ATP-binding cassette-like transporters are involved in the transport of lignin precursors across plasma and vacuolar membranes

Abstract

Lignin is a complex biopolymer derived primarily from the condensation of three monomeric precursors, the monolignols. The synthesis of monolignols occurs in the cytoplasm. To reach the cell wall where they are oxidized and polymerized, they must be transported across the cell membrane. However, the molecular mechanisms underlying the transport process are unclear. There are conflicting views about whether the transport of these precursors occurs by passive diffusion or is an energized active process; further, we know little about what chemical forms are required. Using isolated plasma and vacuolar membrane vesicles prepared from Arabidopsis, together with applying different transporter inhibitors in the assays, we examined the uptake of monolignols and their derivatives by these native membrane vesicles. We demonstrate that the transport of lignin precursors across plasmalemma and their sequestration into vacuoles are ATP-dependent primary-transport processes, involving ATP-binding cassette-like transporters. Moreover, we show that both plasma and vacuolar membrane vesicles selectively transport different forms of lignin precursors. In the presence of ATP, the inverted plasma membrane vesicles preferentially take up monolignol aglycones, whereas the vacuolar vesicles are more specific for glucoconjugates, suggesting that the different ATP-binding cassette-like transporters recognize different chemical forms in conveying them to distinct sites, and that glucosylation of monolignols is necessary for their vacuolar storage but not required for direct transport into the cell wall in Arabidopsis.

Proton-Dependent Coniferin Transport, a Common Major Transport Event in Differentiating Xylem Tissue of Woody Plants

“…Our data also show that such H + -dependent transport is not restricted to angiosperms but occurs in the gymnosperm Japanese cypress. This is contradictory to data from Arabidopsis (Miao and Liu, 2010), in which similar experimental procedures were employed. One possible reason for this discrepancy may be the different plant materials used: Arabidopsis leaves, which are primarily mesophyll cells that do not lignify the cell wall, versus the differentiating xylem of tree species, in which the majority of cells are actively forming lignin.…”

“…Recently, biochemical experiments using microsomal fractions from rosette leaves of Arabidopsis (Arabidopsis thaliana) indicated the possible involvement of an ATPbinding cassette (ABC)-like transporter in the transport of lignin precursors (Miao and Liu, 2010). In Arabidopsis leaves, however, lignification occurs in only a limited number of cells at the leaf vein, and the majority of microsomes are derived from mesophyll cells.…”

Vacuolar Transport of Abscisic Acid Glucosyl Ester Is Mediated by ATP-Binding Cassette and Proton-Antiport Mechanisms in Arabidopsis

“…The glucoside of coniferyl alcohol was shown to be transported into endomembrane-enriched vesicles isolated from differentiating xylem of poplar (Populus spp.) via proton antiporters and into Arabidopsis leaf mesophyll vacuoles via ABC transporters (Miao and Liu, 2010;Tsuyama et al, 2013). Furthermore, concurrent ABC-type and proton-dependent vacuolar transport mechanisms were shown for the flavone diglucoside saponarin (Frangne et al, 2002).…”

Arabidopsis ABCG14 protein controls the acropetal translocation of root-synthesized cytokinins

“…Microsome preparation was followed by the procedure described in Miao and Liu 43 . Briefly, Arabidopsis seedlings (12-DAG) harboring 35S::EGFP-AtABCG14 expression cassette were ground with 50 mM Tris buffer A (pH 8.0) containing 2 mM EDTA, 20% Glycerol, 1 mM DTT and a 1X Protease inhibitor cocktail (PIC).…”