H<sub>2</sub>O<sub>2</sub> regulates activity of the GSK3-like kinase BIN2

Lu et al. unravel a mechanism by which reactive oxygen species modulate brassinosteroid signaling through the GSK3-like kinase BIN2

Qing Lu^a,b, Eugenia Russinova^a,b

^a Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052 Ghent, Belgium

^b Center for Plant Systems Biology, VIB, 9052 Ghent, Belgium

Background: Brassinosteroids (BRs) are steroidal hormones that are essential for plant growth and development. BRs bind and activate the leucine-rich repeat receptor kinase BR INSENSITIVE1 (BRI1) and its coreceptor BRI1-ASSOCIATED KINASE1 (BAK1) to consequently inactivate the constitutively active GSK3-like kinase BR-INSENSITIVE2 (BIN2) and trigger BR responses. The synthetic chemical inhibitor of the plant GSK3-like kinases, bikinin can initiate BR signaling and is broadly used for functional studies of BR hormones.

Question: Although BR signaling pathway is well understood, not all mechanisms that control BIN2 activity are uncovered. Our aim was to find unknow BIN2 regulators via a forward genetic screen for bikinin-resistant mutants in Arabidopsis.

Findings: We discovered that a mutation in the ADENOSINE MONOPHOSPHATE DEAMINASE (AMPD)/EMBRYONIC FACTOR1 (FAC1) gene reduces the sensitivity of Arabidopsis seedlings to both bikinin and BRs. Further studies showed that AMPD regulates BIN2 oligomerization by modulating the homeostasis of the reactive oxygen species (ROS) hydrogen peroxide (H₂O₂). The BIN2oligomer is less active and more sensitive to bikinin, compared to its monomer. In addition, BIN2 phosphorylates AMPD to possibly alter its function. Our study revealed a H₂O₂ homeostasis-mediated regulation loop between AMPD and BIN2 that fine-tunes the BIN2 kinase activity to control plant growth and development.

Next steps, We will further investigate how different types of ROS affect BIN2 activity and what roles these different mechanisms play in plant adaptation to the changing environment