Plant physiologyJul 3, 2013

How non-destructive gibberellin signals help start Arabidopsis seed germination

Longevity & Aging Weekly Brief ↗PubMed ↗DOI ↗

Updated Mar 16, 2026

Abstract

DELLA repression of Arabidopsis seed germination can be lifted through proteolysis or proteolysis-independent hormone signaling.

Gibberellin (GA) binding to GID1 receptors forms a complex that leads to DELLA protein degradation via the ubiquitin-proteasome pathway.
In the sly1-2 mutant, DELLA degradation is impaired, resulting in a strong seed dormancy phenotype linked to high levels of abscisic acid (ABA).
Loss of ABA sensitivity can promote germination in dormant sly1-2 seeds, indicating a role for ABA in their dormancy.
Overexpression of GID1b reduces DELLA levels through a mechanism that does not involve proteolysis, leading to decreased ABA accumulation.
After-ripening increases GA levels and promotes GID1-dependent GA signaling, which may facilitate germination by disrupting DELLA's activation of XERICO, an ABA biosynthesis inducer.

Simplified

DELLA repression of Arabidopsis (Arabidopsis thaliana) seed germination can be lifted either through DELLA proteolysis by the ubiquitin-proteasome pathway or through proteolysis-independent gibberellin (GA) hormone signaling. GA binding to the GIBBERELLIN-INSENSITIVE DWARF1 (GID1) GA receptors stimulates GID1-GA-DELLA complex formation, which in turn triggers DELLA protein ubiquitination and proteolysis via the SCF(SLY1) E3 ubiquitin ligase and 26S proteasome. Although DELLA cannot be destroyed in the sleepy1-2 (sly1-2) F-box mutant, long dry after-ripening and GID1 overexpression can relieve the strong sly1-2 seed dormancy phenotype. It appears that sly1-2 seed dormancy results from abscisic acid (ABA) signaling downstream of DELLA, since dormant sly1-2 seeds accumulate high levels of ABA hormone and loss of ABA sensitivity rescues sly1-2 seed germination. DELLA positively regulates the expression of XERICO, an inducer of ABA biosynthesis. GID1b overexpression rescues sly1-2 germination through proteolysis-independent DELLA down-regulation associated with increased expression of GA-inducible genes and decreased ABA accumulation, apparently as a result of decreased XERICO messenger RNA levels. Higher levels of GID1 overexpression are associated with more efficient sly1 germination and increased GID1-GA-DELLA complex formation, suggesting that GID1 down-regulates DELLA through protein binding. After-ripening results in increased GA accumulation and GID1a-dependent GA signaling, suggesting that after-ripening triggers GA-stimulated GID1-GA-DELLA protein complex formation, which in turn blocks DELLA transcriptional activation of the XERICO inhibitor of seed germination.

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How non-destructive gibberellin signals help start Arabidopsis seed germination

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