Brassinosteroids regulate pavement cell growth by mediating BIN2-induced microtubule stabilization.

Area of Science:

• Plant biology
• Molecular and cell biology
• Biochemistry

Background:

• Brassinosteroids (BRs) are crucial plant steroid hormones regulating development.
• Cytoskeletal organization, particularly microtubules, is vital for plant growth.
• BR deficiency causes phenotypes resembling microtubule defects, suggesting a link.

Purpose of the Study:

• To elucidate the molecular mechanism by which BRs regulate microtubule dynamics and cell morphology.
• To identify specific proteins involved in the interaction between BR signaling and the cytoskeleton.

Main Methods:

• Liquid chromatography-tandem mass spectrometry (LC-MS/MS) to identify interacting proteins.
• In vitro and in vivo pull-down assays to confirm protein-protein interactions.
• High-speed co-sedimentation assays to assess microtubule binding.
• Analysis of Arabidopsis mutants (bin2-3 bil1 bil2 and bin2-1) and wild-type responses to microtubule-disrupting drugs.

Main Results:

• Tubulin proteins were identified as interacting partners of BRASSINOSTEROID INSENSITIVE2 (BIN2).
• BIN2 directly interacts with tubulin proteins and binds to microtubules.
• BIN2 homologs (BIL1 and BIL2) function redundantly with BIN2.
• Mutant analysis revealed that BIN2 mediates microtubule stabilization, affecting sensitivity to oryzalin.

Conclusions:

• BR signaling, through BIN2, directly influences microtubule stability in plants.
• This mechanism is critical for regulating pavement cell and leaf growth.
• The findings reveal a novel role for BRs in cytoskeletal regulation.