Regulation of growth and morphogenesis by gibberellins at the shoot apex – GrowthDynamics

Understanding the molecular mechanisms underlying the construction of multicellular organisms is a central question in biology that can yield key knowledge with a wide range of potential applications ranging from medicine to agriculture. In both plants and animals, the construction of the body plan commonly occurs through rhythmic addition of new segments at the tip of growing structures. However, little is known on whether and how growth contributes to the establishment of rhythmic morphogenesis and thus to the construction of complex eukaryotic organisms. In this fundamental project, we will address this question in plants using the shoot apical meristem (SAM) whose stem cell niche activity controls post-embryonic primary shoot architecture, also known as phyllotaxis, by producing rhythmically new aerial lateral organs and corresponding stem segments. We will focus our analysis on a class of key plant growth regulators, the plant hormone gibberellins (GA), and will elucidate their function in establishing the spatio-temporal dynamics of morphogenesis at the SAM trough growth regulation and in the determination of shoot architecture.
While GA are known to act in the SAM and to impact the dynamics of patterning, the molecular mechanisms underlying growth regulation by GA at the SAM are entirely unknown. To dissect these mechanisms, we will develop a novel GA biosensor and reporters to characterize in details the 4D (3D + time) distribution of GA and GA signaling in the SAM using live-imaging, as well as their regulation. We will map growth patterns in the SAM and will use both pharmacological and genetic approaches to interfere inducibly with GA activity, in order to analyze the causality between GA activity and growth. Interfering with GA activity will also allow us deciphering how GA activity impacts morphogenesis dynamics and thus phyllotaxis and shoot architecture. Finally, a combination of targeted and non-targeted approaches based on protein imunoprecipitation as well as genomics approaches will allow identifying transcription factors targeted directly by GA signaling in the SAM and the downstream gene network mediating growth regulation in this tissue.
The knowledge generated in this project will provide a unique multiscale vision of how growth is coordinated by GA in a plant complex tissue to ensure both stem cell niche maintenance and reiterative organogenesis and of how it contributes to building complex architectures. As GA are required throughout the life of the plant, this knowledge will have a broad impact for the understanding of plant growth.
This multidisciplinary project associates two complementary partners, both from the thematic and from the methodological point of views. The team headed by Teva Vernoux (RDP, Lyon; Coordinator) is expert in hormone signaling and meristem biology and the one headed by Patrick Achard (IBMP, Strasbourg) is focused on gibberellin biology. Moreover, the laboratory in Lyon has an internationally recognized expertise in systems biology and live imaging that complements the biochemistry, cell biology and genomics expertise of the Strasbourg team. These complementarities will yield a high synergy key to the success of the project.