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Structure of the wild-type Arabidopsis ABCB1 in the brassinolide-bound state
Structural highlights
FunctionAB1B_ARATH Auxin efflux transporter that acts as a negative regulator of light signaling to promote hypocotyl elongation. Mediates the accumulation of chlorophyll and anthocyanin, as well as the expression of genes in response to light. Participates directly in auxin efflux and thus regulates the polar (presumably basipetal) auxin transport (from root tips to root elongating zone). Transports also some auxin metabolites such as oxindoleacetic acid and indoleacetaldehyde. Involved in diverse auxin-mediated responses including gravitropism, phototropism and lateral root formation. Confers resistance to herbicides such as dicamba, pendimethalin, oryzalin, and monosodium acid methanearsonate (MSMA), but not to herbicides such as glyphosate, atrazine, bentazon and fluazifop-p-butyl. Mediates also resistance to xenobiotics such as cycloheximide and the cytokinin N6-(2-isopentenyl)adenine (2IP).[1] [2] [3] [4] [5] [6] [7] Publication Abstract from PubMedBrassinosteroids (BRs) are steroidal phytohormones indispensable for plant growth, development, and responses to environmental stresses. The export of bioactive BRs to the apoplast is essential for BR signaling initiation, which requires binding of a BR molecule to the extracellular domains of the plasma membrane-localized receptor complex. We have previously shown that the Arabidopsis thaliana ATP-binding cassette (ABC) transporter ABCB19 functions as a BR exporter and, together with its close homolog ABCB1, positively regulates BR signaling. Here, we demonstrate that ABCB1 is another BR transporter. The ATP hydrolysis activity of ABCB1 can be stimulated by bioactive BRs, and its transport activity was confirmed in proteoliposomes and protoplasts. Structures of ABCB1 were determined in substrate-unbound (apo), brassinolide (BL)-bound, and ATP plus BL-bound states. In the BL-bound structure, BL is bound to the hydrophobic cavity formed by the transmembrane domain and triggers local conformational changes. Together, our data provide additional insights into ABC transporter-mediated BR export. Structural insights into brassinosteroid export mediated by the Arabidopsis ABC transporter ABCB1.,Wei H, Zhu H, Ying W, Janssens H, Kvasnica M, Winne JM, Gao Y, Friml J, Ma Q, Tan S, Liu X, Russinova E, Sun L Plant Commun. 2025 Jan 13;6(1):101181. doi: 10.1016/j.xplc.2024.101181. Epub 2024 , Nov 4. PMID:39497419[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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