Arabidopsis ABCG Transporters, Which Are Required for Export of Diverse Cuticular Lipids, Dimerize in Different Combinations

Abstract

ATP binding cassette (ABC) transporters play diverse roles, including lipid transport, in all kingdoms. ABCG subfamily transporters that are encoded as half-transporters require dimerization to form a functional ABC transporter. Different dimer combinations that may transport diverse substrates have been predicted from mutant phenotypes. In Arabidopsis thaliana, mutant analyses have shown that ABCG11/WBC11 and ABCG12/CER5 are required for lipid export from the epidermis to the protective cuticle. The objective of this study was to determine whether ABCG11 and ABCG12 interact with themselves or each other using bimolecular fluorescence complementation (BiFC) and protein traffic assays in vivo. With BiFC, ABCG11/ABCG12 heterodimers and ABCG11 homodimers were detected, while ABCG12 homodimers were not. Fluorescently tagged ABCG11 or ABCG12 was localized in the stem epidermal cells of abcg11 abcg12 double mutants. ABCG11 could traffic to the plasma membrane in the absence of ABCG12, suggesting that ABCG11 is capable of forming flexible dimer partnerships. By contrast, ABCG12 was retained in the endoplasmic reticulum in the absence of ABCG11, indicating that ABCG12 is only capable of forming a dimer with ABCG11 in epidermal cells. Emerging themes in ABCG transporter biology are that some ABCG proteins are promiscuous, having multiple partnerships, while other ABCG transporters form obligate heterodimers for specialized functions.

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

“…9a). The fluorescence distribution of the fusion protein in leaf epidermal cells agreed well with that revealed by FM4-64 staining, a typical plasma membrane indicator 31 , and also lined up with the adjacent cell wall that was labelled with propidium iodide (PI), the cell wall polysaccharide indicator 31 ( Fig. 4c,d).…”

“…Our attempt to determine AtABCG14's biochemical properties in vitro was unsuccessful. This is probably due to the assay systems that we adopted were not optimal for the effective functional detection or due to the transporter's half-molecular nature and the possible requirement for an unknown hetero-partner for its proper functioning 31 . These technical obstacles currently prevented our unequivocal assessment of its biochemical function; nevertheless, our transport activity assay using detached leaves, in which one set of leaf cells, as the control, was from a wild-type background that showed very low level of (or even negligible) expression of AtABCG14, and the other set of leaves harboured the overexpressed AtABCG14 (about 250-fold higher in its transcripts, compared with the control leaves), does closely resemble a conventional in vitro assay system for examining this transporter's function.…”

Two ATP Binding Cassette G (ABCG) Transporters, OsABCG26 and OsABCG15, Collaboratively Regulate Rice Male Reproduction

“…However, whether OsABCG26 and OsABCG15 function in the same pathway or complex in lipid export still remains to be investigated. We failed to identify an interactional of these two proteins with yeast (Saccharomyces cerevisiae) two-hybrid assays, probably because of no interaction between them or the difficulties in heterologous expression of plant transporters in yeast (McFarlane et al, 2010). Other approaches need to be used in future to solve this specific issue.…”

“…As transporters, ABCG transporters encoded as halftransporter form homodimers or heterodimers with other ABCG transporters. For example, ABCG11 forms homodimers and heterodimers with ABCG12, whereas ABCG12 forms only heterodimers with ABCG11 (McFarlane et al, 2010). Recently, four additional Arabidopsis ABCG proteins were reported to be related to pollen formation, including ABCG9 (Choi et al, 2014), ABCG31 (Choi et al, 2014), ABCG1 (Yadav et al, 2014), and ABCG16 (Yadav et al, 2014).…”

Enhanced cuticle accumulation by employing MIXTA-like transcription factors

“…In addition to the biosynthesis of cutin and wax monomers, the proper transport of cuticular lipids synthesized in the endoplasmic reticulum is necessary for wax and cutin accumulation outside epidermal cells (Bird et al 2007;Pighin et al 2004). An ABC transporter homodimer (ABCG11) and heterodimer (ABCG11-ABCG12) are responsible for the export of cutin and wax, respectively (Bird et al 2007;McFarlane et al 2010). Additionally, the genes encoding these transporters are expressed in epidermal cells (Bird et al 2007;Luo et al 2007;Panikashvili et al 2007;Pighin et al 2004).…”