Brassinosteroid Signaling in Plant Growth and Development

Brassinosteroids are a class of polyhydroxylated steroid hormones essential for regulating plant growth, development and environmental responses. Perception of these ligands at the plasma membrane is mediated by the receptor kinase BRI1 and its co-receptor SERK, which undergo mutual transphosphorylation upon ligand binding. Activation of this receptor complex initiates a cytoplasmic phosphorylation cascade in which the GSK3-like kinase BIN2 is inactivated, allowing dephosphorylated transcription factors such as BZR1 and BES1 to accumulate in the nucleus and modulate the expression of thousands of target genes. This signalling module controls cell elongation, division and differentiation across multiple tissues, including roots, shoots and reproductive organs, and is finely tuned in a spatiotemporal manner to integrate signals from other hormones and abiotic stress pathways. In roots, brassinosteroid activity varies between cell types to balance stem cell maintenance and differentiation, while in aerial tissues it coordinates vascular patterning and organ size. Understanding this pathway has direct implications for crop improvement by manipulating cell growth and stress resilience.

Research from Nature Portfolio

A recent study in maize and Arabidopsis demonstrated that plasma membrane-associated copine proteins of the BONZAI family are integral to brassinosteroid signalling. These proteins directly interact with SERK kinases to stabilise the BRI1–SERK receptor complex and promote efficient transphosphorylation upon ligand recognition. Loss of BON proteins impairs receptor assembly, reducing downstream signalling output and leading to defects in organ growth. Conservation of this mechanism across monocot and dicot species identifies BONZAI proteins as promising targets for enhancing agronomic traits by modulating brassinosteroid responsiveness.

Brassinosteroid Signaling in Plant Growth and Development publication trend

The graph below shows the total number of articles in brassinosteroid signaling in plant growth and development across all publications each year (not limited to Nature Index journals).

Technical terms

Brassinosteroids: Polyhydroxylated steroid hormones that regulate plant growth, development and stress responses.

BRI1: A plasma membrane leucine-rich repeat receptor kinase that binds brassinosteroid ligands.

SERK: A co-receptor kinase that forms a complex with BRI1 and catalyses mutual transphosphorylation upon ligand binding.

Transphosphorylation: Reciprocal phosphorylation between two kinases within a receptor complex, activating downstream signalling.

BIN2: A GSK3-like kinase that phosphorylates and inhibits brassinosteroid-responsive transcription factors in the absence of hormone.

Transcription factor: A protein that binds specific DNA sequences to regulate gene expression.

HASCh-seq: Hybrid allele-specific chromatin binding sequencing, a method to detect allele-specific transcription factor occupancy across the genome.

References

1. Polarity-guided uneven mitotic divisions control brassinosteroid activity in proliferating plant root cells. Cell (2025).
2. Copine proteins are required for brassinosteroid signaling in maize and Arabidopsis. Nature Communications (2024).
3. Hybrid allele-specific ChIP-seq analysis identifies variation in brassinosteroid-responsive transcription factor binding linked to traits in maize. Genome Biology (2023).
4. Mapping the signaling network of BIN2 kinase using TurboID-mediated biotin labeling and phosphoproteomics. The Plant Cell (2023).
5. Brassinosteroids: Multidimensional Regulators of Plant Growth, Development, and Stress Responses[OPEN]. The Plant Cell (2019).