Inactivation of the X chromosome in females is governed by the n–1 rule

TLS Online TPP Program

#Id: 7544

#Unit 6. System Physiology – Plant

Three main classes of mutations affecting plant height have been selected:

Gibberellin-insensitive dwarfs

Gibberellin-deficient mutants in which the gibberellin deficiency has been overcome by a second “suppressor” mutation, so the plants look closer to normal

Mutants with a constitutive gibberellin response (“slender” mutants)

TLS Online TPP Program

#Id: 7545

#Unit 6. System Physiology – Plant

GAI and RGA proteins normally act as repressors of gibberellin responses. Gibberellin acts indirectly through an unidentified signaling intermediate, which is thought to bind to the regulatory domains of the GAI and RGA Proteins. 

TLS Online TPP Program

#Id: 7546

#Unit 6. System Physiology – Plant

TLS Online TPP Program

#Id: 7547

#Unit 6. System Physiology – Plant

TLS Online TPP Program

#Id: 7549

#Unit 6. System Physiology – Plant

In the nucleus, gibberellin binds to the GID1 receptor and induces a conformational change in the N-terminal domain of the receptor, allowing the receptor to interact with the TVHYNP and DELLA domains of the DELLA repressor.

The formation of the GID1-repressor complex promotes the interaction between the repressor and the E3 ubiquitin ligase SCF-SLY, leading to the ubiquitination and degradation of the DELLA repressor by the 26S proteasome.

TLS Online TPP Program

#Id: 7550

#Unit 6. System Physiology – Plant

In the absence of gibberellin, the DELLA proteins positively regulate GID1, GA20ox, and GA3ox (plus signs), and negatively regulate GA2ox (minus sign). Conversely, both bioactive gibberellin and the GID1 receptor enhance DELLA repressor degradation (plus signs), while GA2ox blocks DELLA repressor degradation (minus signs).