- Brassinosteroids are a group of steroid hormones that function in a variety ofcellular and developmental contexts in plants. Which one of the following acts asan inhibitor of the brassinosteroid receptor?
(1) BRI 1 (2) BKI 1
(3) BAK 1 (4)BSK1Correct answer: (2) BKI 1
Explanation:
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BRI1 (Brassinosteroid Insensitive 1) is the main receptor kinase for brassinosteroids and activates signaling upon brassinosteroid binding. It is not an inhibitor but the receptor itself.
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BKI1 (BRI1 Kinase Inhibitor 1) is a negative regulator or inhibitor of the brassinosteroid receptor BRI1. It binds to BRI1 to prevent its activation in the absence of brassinosteroids, thus acting as an inhibitor.
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BAK1 is a co-receptor that associates with BRI1 when brassinosteroids bind, facilitating activation rather than inhibition.
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BSK1 is a downstream kinase phosphorylated by BRI1 to transduce the brassinosteroid signal, not an inhibitor.
BKI1 is a membrane-bound inhibitor protein that binds to the brassinosteroid receptor BRI1 and prevents its activation until brassinosteroid binding occurs, thus tightly regulating the initiation of brassinosteroid signal transduction essential for plant growth and development.
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