Hemibiotrophs have an initial period of biotrophy followed by necrotrophy.

TLS Online TPP Program

#Id: 10230

#Unit 6. System Physiology – Plant

Upon binding brassinolide, homodimers of BRI1 are activated and heterooligomerize with the RLK BRI1-ASSOCIATED RECEPTOR KINASE1 (BAK1)

TLS Online TPP Program

#Id: 10231

#Unit 6. System Physiology – Plant

BIN2 is a serine/threonine protein kinase that, in the absence of brassinolide, negatively regulates the closely related transcription factors BES1 and BZR1 by phosphorylation.

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#Id: 10232

#Unit 6. System Physiology – Plant

In the presence of brassinolide, the activated phosphatase BSU1 dephosphorylates BIN2 and promotes its degradation by the 26S proteasome system, thus blocking its activity. BES1 and BZR1

are then dephosphorylated by PROTEIN PHOSPHATASE2A

(PP2A), and the active forms of BES1 and BZR1 move into the nucleus where they regulate the expression of brassinolide response genes

TLS Online TPP Program

#Id: 10233

#Unit 6. System Physiology – Plant

BES1 & BZR1 give BR response

Phosphorylated BIN2 inhibits BES1 & BZR1 

Phosphorylated BIN2 is degraded by BSU1 

BSK proteins activate BSU1 phosphatase.

BRI1–BAK1-BR complex activates BSK

TLS Online TPP Program

#Id: 10234

#Unit 6. System Physiology – Plant

BRI1–BAK1-BR-→ BSK--→BSU1--→degradation of Phosphorylated BIN2-----→activation of BES1 & BZR1--→BR Response

TLS Online TPP Program

#Id: 10235

#Unit 6. System Physiology – Plant

Brassinosteroids, like gibberellins, suppress photomorphogenesis in the dark.