Gibberellins and adaptation to environment

Group leader : Patrick ACHARD

Research area

Plant growth is subject to hormonal control and must adapt to environmental cues (nutrient availability, water supply, light, temperature) or stress. Major developmental growth regulators are the gibberellins (GAs), a family of tetracyclic diterpenoid molecules that play important roles in diverse developmental processes such as seed germination, growth and the induction of flowering. Hence, mutant plants that are deficient in GAs exhibit a dwarf and late flowering phenotype, and treating these plants with GAs restores normal growth. The role of GAs in determining plant stature had major impacts on agriculture in the 1960’s, and the development of semi-dwarf varieties that show altered GA responses contributed to a huge increase in grain yields during the “green revolution”. During the past decade, substantial progress has been made in understanding the GA metabolism, transport and signaling cascade, from GA perception to the activation of transcriptional networks that regulate plant development. Our group is mostly focused on the mechanisms allowing GA-responsive growth under different environmental conditions. We are also investigating the transport of GAs in plants, particularly the long-distance movement of endogenously made GAs across plant organs.


Regulatory mechanisms of GA/DELLA action

The phytohormone GA has long been known to control growth by stimulating the degradation of nuclear growth-repressing DELLA proteins, however the mechanism allowing GA-responsive growth is only slowly emerging. An important function of DELLAs relies on their ability to establish protein-protein interaction with diverse classes of regulatory proteins and transcription factors. By doing so, DELLAs control the expression of a multitude of target genes functioning in distinct pathways. Our goal is to unravel through genetics and cell imaging the specificity, consequence and dynamics of these interactions in planta.

Plant adaptation to environmental stress

Plants are sessile organisms and hence cannot escape unfavorable growth conditions. To overcome these limitations, plants have the potential to acclimate by triggering a cascade of events leading to changes in gene expression and biochemical modifications. Recent advances have revealed the role of GA/DELLA in many aspects of plant growth that are influenced by environmental stress. For example, whereas the growth of DELLA loss-of-function mutants is less inhibited by salt stress than wild-type, DELLA function promotes survival. We proposed that DELLAs permit flexible and appropriate modulation of growth in response to environmental changes. We are currently investigating using multidisciplinary approaches the regulatory mechanisms by which GA/DELLA integrate and convey information from multiple environmental signals.

Transport of GAs in plants

Plant hormones are low abundant signaling compounds that often move throughout the body of the plant from production sites to recipient tissues or organs. Historically identified in the pathogenic fungus Gibberella fujikoroi, the causal agent of the bakanae disease of rice, 136 GAs have been described in plants, fungi and bacteria, although only a few GAs have biological activity. We recently showed through micrografting and biochemical approaches that the GA precursor GA12, although biologically inactive, is the major mobile GA signal over long distances in Arabidopsis. We now combine genetic and pharmacological approaches to unravel the properties and the biological functions associated with this transport.