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The BRI1 gene is expressed throughout the plant.
BRL1 and BRL3 are primarily expressed in vascular tissues.
Reproduced with permission from Cañ o-Delgado, A., Yin, Y., Yu, C., Vafeados, D., Mora-Garcí a, S., Cheng, J.-C., Nam, K.H., Li, J., and Chory, J. (2004). BRL1 and BRL3 are novel brassinosteroid receptors that function in vascular differentiation in Arabidopsis. Development 131: 5341-5351.
Bishop, G.J., and Koncz, C. (2002). Brassinosteroids and plant steroid hormone signaling. Plant Cell 14: S97-110.
Two additional BR receptors have restricted expression patterns
Binding of BL to BRI1 causes BKI1 to dissociate from it
No BL 5 min BL 10 min BL
Receptor (BRI1)
P P
In the absence of BL, BKI1 (labeled with YFP) is at the plasma membrane.
Nakamura, A., Fujioka, S., Sunohara, H., Kamiya, N., Hong, Z., Inukai, Y., Miura, K., Takatsuto, S., Yoshida, S., Ueguchi-Tanaka, M., Hasegawa, Y., Kitano, H., and Matsuoka, M. (2006). The role of OsBRI1 and its homologous gGenes, OsBRL1 and OsBRL3, in rice. Plant Physiol. 140: 580-590.
BRI1 signaling requires activation by a coreceptor BAK1; BAK1 is also a plasmamembrane associated kinase
Extracellular domain Cytoplasmic protein kinase domain
The BRI1 gene was identified through map-based cloning
BRI1
Reprinted from Li, J., and Chory, J. (1997). A putative leucine-rich repeat receptor kinase involved in brassinosteroid signal transduction. Cell 90: 929-938, with permission from Elsevier; Bishop, G.J., and Koncz, C. (2002). Brassinosteroids and plant steroid hormone signaling. Plant Cell 14: S97-110.
Summary – BR receptor action
Low BR
Low BR levels – receptor inactive and inhibited by BKI1
Wang, X., and Chory, J. (2006) Brassinosteroids regulate dissociation of BKI1, a negative regulator of BRI1 signaling, from the plasma membrane. Science 313:1118-1122. Reprinted with permission from AAAS
The rice BRL genes have a different expression pattern than BRI1
osbri1
osbri1
The rice OsBRI1 gene is preferentially expressed in shoots. A loss-of-function mutant shows severe dwarfing in the shoot but little change in root growth, suggesting an organ-specific role for OsBRL1 and OsBRL3.
The BRI1 receptor is a plasmamembrane localized LRR-RLK
BRI1 is a Leucine-rich repeat – receptor like kinase (LRR-RK) Leucine-rich repeat (LRR)
bri1
Trans-membrane domain Kinase Domain
bri1 loss-offunction mutant
Rescued by BRL1 or BRL3 expressed from BRI1 promoter
The BRL genes may encode receptors with cell-specific functions.
Reproduced with permission from Cañ o-Delgado, A., Yin, Y., Yu, C., Vafeados, D., Mora-Garcí a, S., Cheng, J.-C., Nam, K.H., Li, J., and Chory, J. (2004). BRL1 and BRL3 are novel brassinosteroid receptors that function in vascular differentiation in Arabidopsis. Development 131: 5341-5351.
The structure and related mutants of BRI1
By contrast, animal steroid receptors are intracellular
Steroids freely cross plasma membrane Steroid receptor
Wen-Hui Lin whlin@ 2014-09
Plant Steroid Hormones
Brassinosteroid signaling
A nice overview
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Reprinted from Gudesblat, G.E., and Russinova, E. (2011). Plants grow on brassinosteroids. Curr. Opin. Plant Biol. 14: 530-537 with permission from Elsevier.
Graduate Level Course Plant Signal Transduction
Example for hormone signal transduction and hormonal regulating plant development: Brassinosteroids (BR)
PLANT LRR-RLKs are very abundant in plant and animal cells and bind a wide variety of signaling molecules. In plants LRR-RLKs are involved in developmental signaling and pathogen responses. ANIMAL
BRI1
BAK1
BAK1 was identified by an activation screenபைடு நூலகம்– a screen for plants that partially reverse the dwarf bri1-5 phenotype when overexpressed.
BAK1 has a cytoplasmic protein kinase domain but a smaller extracellular domain that does not bind BR.
When the receptor binds the hormone, the complex moves into nucleus, binds DNA and initiates transcription
Leucine-rich repeat receptor-like kinases (LRRRLKs) are prevalent
BRI1 signaling is negatively controlled by BKI1
Receptor (BRI1)
Low BR
Inhibitor (BKI1)
Wild-type BKI1 Arabidopsis overexpression BKI1 was identified through a search for proteins that physically interact with BRI1.
The protein encoded by BRL1 and BRL3 can function as receptors
