Gibberellin implication in plant growth and stress responses

Abstract

Hormones gibberellins (GAs) are a class of diterpenoid acids that control many aspects of plants' life, including both developmental processes and stress responses. Nowadays, we have a good understanding of how GA levels are regulated and how this information is translated into physiological responses, mainly through genetic and biochemical approaches carried out during the last two decades in rice and Arabidopsis. Here, we review the current knowledge of the GA pathway from GA metabolism to the downstream responses and pay special attention to the regulatory molecular mechanisms. GA biosynthesis starts in plastids, whereas its last steps, and also the GA inactivation, take place in the cytosol. Importantly, the expression of gene coding enzymes that catalyze limiting steps, for example, the soluble GA 20-oxidases, is usually regulated by environmental cues, making the GA level very sensitive to changes in the environment. The binding of the hormone to the GID1 receptor provokes the degradation of the master negative regulators in the pathway, the transcriptional regulators DELLA proteins, and GA-promoted responses proceed. The biochemical basis of the GID1-GA-DELLA regulatory module is well established, but how DELLA proteins regulate downstream events is a matter of current intensive research. In this regard, the regulation of transcription factors' activity through direct physical interaction seems to be an extended yet not unique mechanism of DELLA action. Finally, how all this wealth of information is being used with biotechnological purposes is also discussed.