Role of miR156-targeted SQUAMOSA PROMOTER BINDING PROTEIN-LIKE transcription factors in floral transition

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Flowering is one of the major decisions in a plant’s life cycle and is required for producing the seeds and fruits that support life on earth. It is important to understand the mechanism of this process so that ways can be found to respond to the challenges of climate change and to the pressures on agriculture from an ever-increasing population. In many species, plants make a unique type of leaf before making flowers. This phase is the initial stage of reproductive development, and may be quite short in an annual plant, but is extended in long-lived perennial plants, many of which are of considerable ecological and economic importance. This project will investigate how a group of proteins, known as SPB box transcription factors, specify this initial stage of reproductive development in the model genetic system, Arabidopsis thaliana. Discoveries in model systems can provide key information that can be translated to crop plants in the future. In addition to providing new insights into the mechanism of flowering, this project will provide training opportunities for a postdoctoral researcher, a graduate student, and undergraduate students. Some of the mutants studied in this project have visible phenotypes and could be used to study genetics and plant development in K-12 classrooms. One to two K-12 schoolteachers from South Carolina will be engaged in this project each summer, with guidance on how to apply some materials from the project in their classrooms. As a plant grows, the shoot apical meristem produces lateral organs (leaves and axillary buds) with different developmental identities—juvenile leaves, adult leaves, cauline leaves and flowers. In Arabidopsis, the transition between the juvenile vegetative (V1) and adult vegetative (V2) phase is regulated by miR156 and its targets, SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors, whereas the transition between the cauline leaf (V3) and floral (R) phase is regulated by the floral meristem identity genes, LEAFY and APETALA1. Flowering-time genes regulate the V2 to V3 transition (floral induction), but genes that specify the identity of V3 organs (cauline leaves, secondary inflorescences) are still largely unknown. Mutations in SPL2/SPL9/SPL13/SPL15 produce rosette-like cauline leaves, suggesting that these miR156-targeted SPLs play a key role in promoting the V2 to V3 transition by specifying the V3 organ identity. This project will use a combination of molecular, genetic and biochemical approaches to identify the upstream regulators and downstream targets of these SPLs involved in specifying V3 organ identity. This project is jointly funded by the Plant, Fungal and Microbial Developmental Mechanisms Program and the Established Program to Stimulate Competitive Research (EPSCoR).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.