How boundaries regulate plant architecture

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Agriculture is a key sector of the Canadian economy. Increased productivity is a major goal of breeding programs. Plant architecture is a major determinant of crop yield. The long-term objective of my research program is to understand how genes control plant shape and form. This information is valuable in genomics-assisted breeding which seeks to use knowledge of genes and genomes to customize agronomic traits in crop plants.Plant shape and form relies on the activity of self-perpetuating groups of stem cells called meristems. Meristems provide a continuous supply of daughter cells for incorporation into new leaves, flowers, and shoots throughout the life cycle. Our work focuses on the role of organ boundaries located at the meristem periphery. Boundaries are narrow domains of restricted growth that separate the meristem from new organs as they form. These domains are essential for meristem maintenance and organ outgrowth. These domains are also the source of axillary meristems that give rise to branches and flowers on the inflorescence and the site of abscission zones that control the detachment of fruits, leaves, and flowers. Despite the agronomic importance of boundaries to plant architecture, little is known about the genetic networks that control their function. Our work has identified BLADE-ON-PETIOLE (BOP) transcription factors and their downstream targets as major determinants of plant architecture functioning at organ boundaries. This module regulates reproductive meristem development, inflorescence branching, and specification of abscission zones. A much broader role for this module in fruit development, organ detachment, and plant defense is suggested by expression patterns and transcriptome analysis of downstream target genes. Over the next five years, we will investigate these links in the model plant species, Arabidopsis thaliana (Arabidopsis). Our proposed research focuses on four areas: (1) Role of the BOP module in fruit development, (2) Module function in abscission, (3) TGA transcription factors acting as BOP co-factors at boundaries, and (4) Role of BOPs in plant defense. This work provides important training opportunities for 3 Ph.D. students, 3 M.Sc. students, and 3-4 undergraduate HQP per year who will take an active role in knowledge discovery. Significance: BOPs have been identified as regulating a variety of important agronomic traits linked to crop yield including tillering in barley, leaf complexity and inflorescence architecture in tomato, and abscission in legumes. An understanding of how these genes control development at boundaries brings us one step closer to customization of plants for agriculture.