OCTOPUS regulates BIN2 to control leaf curvature in Chinese cabbage

Area of Science:

• Plant Genetics
• Molecular Biology
• Agronomy

Background:

• Heading is a key agronomic trait in Chinese cabbage, involving essential leaf axial growth.
• Previous research on heading-related genes relied on Arabidopsis studies, with no genes mapped via forward genetics in Chinese cabbage.
• Leaf axial growth and curvature are critical for heading development.

Purpose of the Study:

• To characterize the inward curling mutant 'ic1' in Chinese cabbage (Brassica rapa ssp. pekinensis).
• To identify the gene responsible for the 'ic1' mutation using map-based cloning.
• To elucidate the molecular mechanism of leaf axial growth regulation during the heading stage.

Main Methods:

• Map-based cloning was employed to identify the causative gene in the 'ic1' mutant.
• Genetic analysis and characterization of the inward curling phenotype.
• Investigation of the interaction between BrOPS, brassinosteroid (BR) signaling components (BrBIN2, BrBES1), and downstream genes (BrAS1).

Main Results:

• A mutation in the OCTOPUS (BrOPS) gene was identified as the cause of the 'ic1' inward curling phenotype.
• BrOPS regulates leaf curvature in Chinese cabbage, a function distinct from its role in Arabidopsis phloem differentiation.
• In 'ic1' mutants, impaired BrOPS function prevents brassinosteroid insensitive 2 (BrBIN2) sequestration, leading to constitutive brassinosteroid signaling and inward leaf curling.

Conclusions:

• BrOPS positively regulates brassinosteroid signaling by antagonizing BrBIN2.
• This antagonism promotes leaf epinastic growth at the early heading stage in Chinese cabbage.
• The study identifies BrOPS as a key regulator of heading development through its role in brassinosteroid-mediated leaf axial growth.