Mitchell was isolated from rape (Brassica napus) pollen and showed extremely high biological activity in biological tests
1979
Grove (1979) determined the structure of brassinoid and named it brassinosteroid
1998
The 13th International Annual Conference on Plant Growth substances was officially recognized as the sixth plant hormone.
Types and Structure of Ethylene
Brassinolide (BL)
Castasterone (CS)
Biosynthesis of BR
Multiple pathways for BR synthesis
Many BR-synthesis enzymes are cytochrome P450s (CYPs)
Regulation and Metabolism of BR
There are several pathways for BL deactivation
BRs are deactivated by reversible conjugation and irreversible modifications
BRs may also be deactivated by glucosylationand other reactions
Transport of BR
Endogenous BR is not transported long-distances
Perception and signaling
Receptor
BRI1 is BR receptor
Pathway
Description
Activated BRI1 kinase triggers a kinase cascade that activates key transcription factors
BIN2 kinase targets BES1, BZR1 and other transcription factors
When transcription factors BZR1 and BES1are phosphorylated (left) they are inactive and degraded or sequestered. When dephosphorylated they are active and move into nucleus
Without BR
BR signaling
Physiological Function
BRs regulate diverse processes that include cell elongation, growth, developmental patterning and cell differentiation
Many BR effects are mediated by cross-talk with other hormones, or transcriptional responses
