[Campbell Biology P.902] Based on the description of ctr mutants, what is the normal functio... | Practice Question

Based on the description of ctr mutants, what is the normal function of the protein kinase encoded by the wild-type CTR gene in ethylene signal transduction?

  • A: It directly activates the triple response pathway when ethylene is absent.
  • B: It is a positive regulator that promotes the triple response upon ethylene binding.
  • C: It is a negative regulator that inhibits the triple response when ethylene is absent.
  • D: It synthesizes ethylene to induce the triple response.

Explanation

The text states: 'The fact that this mutation activates the ethylene response suggests that the normal kinase product of the wild-type allele is a negative regulator of ethylene signal transduction. Thus, binding of the hormone ethylene to the ethylene receptor normally leads to inactivation of the kinase, and the inactivation of this negative regulator allows synthesis of the proteins required for the triple response.' This means that normally, when ethylene is absent, the kinase is active and inhibits the triple response. When ethylene is present, it inactivates the kinase, thereby releasing the inhibition and allowing the triple response to occur.