Correct option is D
Explanation-
DELLA proteins are negative regulators of GA signaling. GID1 is the GA receptor. Binding of GA to GID1 promotes the interaction with DELLA proteins. This GA–GID1–DELLA complex leads to ubiquitination and degradation of DELLAs via the 26S proteasome, thus allowing GA responses.
Statement A - DELLA proteins negatively regulate GA signaling. - True
DELLA proteins inhibit GA responses by repressing downstream transcription factors. Their degradation is necessary for GA-mediated growth.
Statement B - Degradation of GA receptor (GID1) is mediated by DELLA proteins. - False
GID1 is not degraded by DELLA proteins. Instead, GA binds to GID1, and the GA–GID1 complex binds DELLA, targeting DELLA for degradation. DELLA proteins don’t mediate GID1 degradation.
Statement C - Ubiquitination and subsequent degradation of DELLA proteins are independent of GID1. - False
This is incorrect. The interaction between DELLA and GID1 (after GA binding) is essential for DELLA's ubiquitination and degradation. Without GID1, DELLA proteins are not targeted for destruction.
Statement D - GA binding to GID1 promotes binding of GID1 to DELLA proteins. - True
GA binds to GID1, causing a conformational change that allows GID1 to bind DELLA. This complex is then recognized by an SCF E3 ubiquitin ligase (SCF^SLY1/GID2), leading to DELLA degradation.
Final Correct Answer: option d
Statements A and D are correct.
