Control of Shoot apex indeterminacy by TERMINAL FLOWER1

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Shoot architecture – the branching pattern of a shoot and when/where it forms flowers - is important for plants in natural environments to make sufficient offspring in the growing season and for yield (biomass or fruits/seeds) in crops. The Wagner lab is investigating a protein that regulates shoot architecture in all flowering plants. The long-term goal of this project is to precisely modulate shoot architecture for different environmental conditions and for different plant uses, leafy vegetables and biofuels on one hand or fruits and grains on the other. To achieve this goal, the lab is coupling inducible genetic manipulations with high resolution spatial and temporal measurements changes in the accumulation of unknown regulators of shoot architecture that will help fine-tune this process. Besides finding sustainable solutions for enhancing food security, societal benefits include training 20 undergraduate students in research important for this proposal in two semester-long Course-based Undergraduate Research Experiences (CURE) laboratory courses. Based on in vivo data and modeling, a key determinant of shoot architecture is the time at which the main shoot and the lateral primordia adopt floral fate. Work by many laboratories points to a pivotal role of the TERMINAL FLOWER1 gene and its orthologs in preventing determinacy (flower fate) of the shoot apex. In tfl1 mutants, the shoot becomes a terminal flower leading to differentiation of the above ground stem cell pool. In this proposal we address the fundamental developmental biology question how maintenance (indeterminacy) or differentiation (determinacy) of the stem cells in the shoot apex are controlled by TFL1. Moreover, reduced TFL1 accumulation or activity revolutionized several crops including tomato, soybean, and cotton because shoot determinacy enables sustainable yield increases by allowing dense planting. Yet how TFL1 accumulation is controlled is poorly understood. We will identify enhancers and transcription factors that promote TFL1 upregulation in the shoot apex. It is also not known how TFL1 blocks determinacy. We will define key direct TFL1- repressed genes and pathways in the shoot that promote differentiation of the stem cell pool containing shoot apex. Insight gained will advance understanding of the switch from stem cell maintenance to differentiation at the shoot apex, how shoot architecture is controlled, and help enable future tailored engineering of agronomically important traits.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.