4 - Gibberellins

Abstract

Gibberellins (GAs), a class of diterpenoid phytohormones, produced by plants and some fungi play an important role in modulating diverse processes throughout plant growth and development. So far, up to 136 different gibberellin molecules have been discovered, only a few of which are bioactive, such as GA1, GA3, GA4, and GA7. Recent studies on GA biosynthesis, metabolism, transport, and signaling, as well as cross talk between GA and other plant hormones and environmental cues have achieved great progress along with the advancement of molecular genetics and functional genomics. Accumulating evidences suggest that the “de-repression” model makes it possible to explain signal transduction mechanisms in GA action. Bioactive GAs promote plant growth and development by promoting the degradation of the DELLA proteins, a family of nuclear growth repressors. The GA signal is perceived by the soluble receptor protein GIBBERELLIN INSENSITIVE DWARF1 (GID1) that undergoes a conformational change and then promotes GA-GID1-DELLA association with the Skp1-Cullin-F-box (SCF) E3 ubiquitin-ligase complex via the F-box protein (SLEEPY1 [SLY1] in Arabidopsis and GIBBERELLIN INSENSITIVE DWARF2 [GID2] in rice), thereby targeting the DELLA proteins for degradation via the 26S proteasome pathway. Evidence also shows that GAs act as mobile molecules that can pass through the plasma membrane for cell-to-cell transport. In this chapter, we focus on findings on GA biosynthesis, perception, and signal transduction pathways, highlighting how the evolutionary conserved GA-GID1-DELLA regulatory module is connected to developmental and environmental responses.