New study elucidates the role of Arabidopsis ABCB19 as brassinosteroid exporter 

Ghent, Belgium 25/03/2024 – Brassinosteroids are steroidal phytohormones required for the growth and development of plants, and are widely used in agriculture to improve crop yields. They are synthesized in the cell interior but binding their receptors at the cell surface. While brassinosteroids were discovered over 50 years ago, research on the mechanisms exporting them out of the cell lagged for decades. Researchers have now uncovered a role for the Arabidopsis ABC transporter ABCB19, formerly known as an auxin transporter, in brassinosteroid export. Their findings have been published in Science this week.  

Brassinosteroid hormones regulate many processes in plants’ physiology, development, and adaptation to biotic and abiotic stresses. Brassinosteroid signaling is initiated at the cell surface, but they are synthesized in the cell interior. This raises the question of how brassinosteroids can reach the apoplast to bind to their receptors. Previous research in other organisms reported that ATP-binding cassette (ABC) transporters can transport steroids in humans and Drosophila. This indicates that transporters may also be required for brassinosteroid export in plants. ​ 

The ABCB transporters are membrane-bound proteins that utilize ATP to actively transport various substrates. In Arabidopsis, 29 ABCBs have been identified, of which ABCB1, ABCB4, and ABCB19 have been characterized as auxin transporters. Researchers from VIB-UGent Center for Plant Systems Biology and The University of Science and Technology of China have now corroborated the role of Arabidopsis ABCB19 as a key player in brassinosteroid export. ​ 

So far, most of the research in the field has been focused on elucidating brassinosteroid biosynthesis and signaling with little consideration about brassinosteroid distribution. Distribution and precise concentration gradients of phytohormones are essential for development. Now we are just beginning to understand the molecular mechanisms of cellular exit and short-distance transport of brassinosteroids in plant cells – Prof. Jenny Russinova, group leader of the Brassinosteroids lab at VIB-UGent Center for Plant Systems Biology (Belgium) 
This is a surprising, yet exciting finding. The role of ABCB19 has been described in the transport of another phytohormone auxin in previous studies. We now corroborated that ABCB19 also functions as a brassinosteroid exporter, thus answering the key question how active brassinosteroids get into the extracellular space to trigger its signaling pathway. ​ – Prof. Linfeng Sun, group leader of the structural biology lab at University of Science and Technology of China (China) 

The role of ABCB19 was studied through stimulation of ABCB19 ATPase activities, in vitro and in planta binding and transport assays, cryo-electron microscopy, and genetic analysis.

With the power of cryo-electron microscopy, we revealed the 3D architecture of ABCB19 and how it binds brassinolide. It is quite surprising that a transporter believed to function in the transport of another essential phytohormone auxin, has a hidden function as a brassinosteroid transporter. – Dr. Xin Liu, from Linfeng Sun’s group at University of Science and Technology of China (China) 

However, the exact mechanism of ABCB19-mediated brassinosteroid transport remains elusive. ​ 

Future research will unravel the mechanisms regulating the ABCB19 activation and substrate preference and hopefully identify additional brassinosteroid exporters. Such mechanisms will help us design more effective strategies for improving plant productivity and resilience via modulating endogenous brassinosteroid amounts and distribution. – Prof. Jenny Russinova, group leader of the Brassinosteroids lab at VIB-UGent Center for Plant Systems Biology (Belgium) 


DOI: 10.1126/science.adj4591

Steve Bers

Steve Bers

Science Communications Expert, VIB

About the VIB-UGent Center for Plant Systems Biology

The VIB-UGent Center for Plant Systems Biology wants to gain insight into how plants grow and respond to the environment. Scientists study how leaves and roots are formed, which micro-organisms live on and around the plant and which substances the plant makes. They map out the genetic diversity of the plant kingdom. This knowledge can lead to sustainable innovations in agriculture and food.

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VIB’s core mission is to generate disruptive insights in the molecular underpinning of life and to translate these actively into impactful innovations for patients and society. VIB is an independent research institute where some 1,800 top scientists from Belgium and abroad conduct pioneering basic research. As such, they are pushing the boundaries of what we know about molecular mechanisms and how they rule living organisms such as human beings, animals, plants, and microorganisms. Based on a close partnership with five Flemish universities – Ghent University, KU Leuven, University of Antwerp, Vrije Universiteit Brussel, and Hasselt University – and supported by a solid funding program, VIB unites the expertise of all its collaborators and research groups in a single institute. VIB’s technology transfer activities translate research results into concrete benefits for society such as new diagnostics and therapies and agricultural innovations. These applications are often developed by young start-ups from VIB or through collaborations with other companies. This also leads to additional employment and bridges the gap between scientific research and entrepreneurship. VIB also engages actively in the public debate on biotechnology by developing and disseminating a wide range of science-based information. 

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About VIB

VIB is an independent research institute that translates insights in biology into impactful innovations for society. Collaborating with the five Flemish universities, it conducts research in plant biology, cancer, neuroscience, microbiology, inflammatory diseases, artificial intelligence and more. VIB connects science with entrepreneurship and stimulates the growth of the Flemish biotech ecosystem. The institute contributes to solutions for societal challenges such as new methods for diagnostics and treatments, as well as innovations for agriculture. 

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