ATP-binding cassette G23 is required for Arabidopsis seed coat suberization

Suberin is an extracellular hydrophobic polymer deposited in seed coats that acts as a barrier to regulate the movement of ions, water, and gases, and protects seeds against pathogens. However, the molecular mechanisms underlying suberin deposition in the seed coat remain unknown. In this study, the in planta role of ATP-binding cassette G23 (ABCG23) was investigated in the Arabidopsis seed coat. ABCG23 transcripts were predominantly expressed in the outer integument1 (oi1) of seed coats and the endodermal cells of roots. The fluorescence of the eYFP:ABCG23 construct was observed in the plasma membranes of the tobacco epidermis, seed coat oi1, and root endodermal cells. Seed coats of abcg23-1 and abcg23-2 mutants exhibited reduced autofluorescence under UV light and increased permeability to tetrazolium salts. Total suberin loads and major suberin components, C24 ω-hydroxy fatty acids and 1, ω-dicarboxylic acids were significantly decreased in the mutant seed coats. The ratio of seed germination and seedling establishment of abcg23-1 and abcg23-2 was significantly reduced compared to the WT under salt and osmotic stress conditions. The bimolecular fluorescence complementation assay showed homodimeric interactions of ABCG-2, -6, -20, and -23 and heterodimeric interactions between ABCG23 and ABCG-2, -6, -11, or -20. Our findings indicate that ABCG23 contributes to the transport of suberin monomers in the Arabidopsis seed coats.