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Title: The roles of the GA receptors GID1a, GID1b, and GID1c in sly1-independent GA signaling

Author
item HAUVERMALE, AMBER - Washington State University
item ARIIZUMI, TOHRU - University Of Tsukuba
item Steber, Camille

Submitted to: Plant Signaling and Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2014
Publication Date: 2/12/2014
Citation: Hauvermale, A., Ariizumi, T., Steber, C.M. 2014. The roles of the GA receptors GID1a, GID1b, and GID1c in sly1-independent GA signaling. Plant Signaling and Behavior. 9:e28030; PMID: 24521922.

Interpretive Summary: Gibberellin (GA) hormone signaling occurs through proteolytic and non-proteolytic signaling mechanisms when the GA receptor GID1 (GA-INSENSITIVE DWARF 1) binds GA. GA binding to GID1 protein causes a conformational change, enabling GID1 to bind negative regulators of GA responses called DELLA proteins. In proteolytic GA signaling, the SLEEPY1 (SLY1) F-box protein recognizes and ubiquitinates DELLA proteins that are in the GID1-GA-DELLA complex, thereby targeting DELLA for destruction via the ubiquitin-proteasome pathway. GA fails to target DELLA proteins for destruction in sly1 mutants. However, sly1 mutant phenotypes are not as severe as those of the gid1a gid1b gid1c knockout of all three Arabidopsis GA receptors nor of the strong GA biosynthesis mutants, suggesting that some non-proteolytic GA signaling occurs when DELLA cannot be destroyed. This “non-proteolytic” GA signaling in the absence of DELLA destruction requires GA and GID1 gene function. The relative roles of GID1a, GID1b, and GID1c in proteolytic and non-proteolytic GA signaling were compared based on the phenotypes of gid1a, gid1b, and gid1c single and multiple mutants to phenotypes of sly1 gid1 double and triple mutants described in previous studies. GID1a is highly important in both cases, but GID1b is more important than GID1c for non-proteolytic GA signaling. GID1b overexpression more strongly rescued the stem elongation and germination phenotypes of sly1 than GID1a and GID1c overexpression. The strong role of GID1b in non-proteolytic GA signaling may result from the fact that GID1b has higher affinity for GA and for DELLA proteins than GID1a and GID1c.

Technical Abstract: Gibberellin (GA) hormone signaling occurs through proteolytic and non-proteolytic signaling mechanisms when the GA receptor GID1 (GA-INSENSITIVE DWARF 1) binds GA. GA binding to GID1 protein causes a conformational change, enabling GID1 to bind negative regulators of GA responses called DELLA proteins. In proteolytic GA signaling, the SLEEPY1 (SLY1) F-box protein recognizes and ubiquitinates DELLA proteins that are in the GID1-GA-DELLA complex, thereby targeting DELLA for destruction via the ubiquitin-proteasome pathway. GA fails to target DELLA proteins for destruction in sly1 mutants. However, sly1 mutant phenotypes are not as severe as those of the gid1a gid1b gid1c knockout of all three Arabidopsis GA receptors nor of the strong GA biosynthesis mutants, suggesting that some non-proteolytic GA signaling occurs when DELLA cannot be destroyed. This “non-proteolytic” GA signaling in the absence of DELLA destruction requires GA and GID1 gene function. The relative roles of GID1a, GID1b, and GID1c in proteolytic and non-proteolytic GA signaling were compared based on the phenotypes of gid1a, gid1b, and gid1c single and multiple mutants to phenotypes of sly1 gid1 double and triple mutants described in previous studies. GID1a is highly important in both cases, but GID1b is more important than GID1c for non-proteolytic GA signaling. GID1b overexpression more strongly rescued the stem elongation and germination phenotypes of sly1 than GID1a and GID1c overexpression. The strong role of GID1b in non-proteolytic GA signaling may result from the fact that GID1b has higher affinity for GA and for DELLA proteins than GID1a and GID1c.