Genetic and hormonal control of maize inflorescence and root development

Crop species such as maize, rice, and wheat are the major sources of global food and, therefore, crucial to human society and civilization. In the United States, maize is the most important crop species, based on area and production value. Understanding maize architecture and development is important for fine-tuning maize architecture to improve crop production and benefit farmers. Auxin, a plant growth hormone, plays a major role in determining maize architecture by affecting every aspect of development, including shoot, root, and inflorescence. Over several decades, studies have been conducted to uncover the mode of auxin action and the genes involved. To date, we know that auxin is a signaling molecule, and that coordinated steps in auxin biosynthesis, transport, signaling, and response are required to affect plant development. However, most of the information we have comes from studies in Arabidopsis, a non-crop species, and there remains a large gap in our knowledge of the auxin pathway in maize and other crop species. Understanding the mechanism of the auxin pathway in maize, a grass, is beneficial not only for maize improvement but also for other grasses like rice and wheat, as they share a common lineage and conserved gene and protein functions across many biological processes. In chapter 1, I review the auxin pathway and role of auxin in plant development with a focus on Arabidopsis, maize, and rice, and highlight the knowledge gap in grasses. In chapter 2, I describe the phenotypic and functional characterization of the enhancer of spi1 (eos1) gene in the maize tassel. The eos1 gene is involved in auxin transport and affects branching and spikelet initiation in maize tassels, directly impacting pollen production and, in turn, crop yield. In chapter 3, I describe the phenotypic and functional characterization of the lateral rootless2 (lrs2) gene in maize, which is also involved in auxin transport but in seedling root development. Seedling roots provide mineral nutrients, water, and anchorage, and ensure seedling establishment, the first step in growth in soil. This is the first study of both genes in maize. Finally, in chapter 4, I offer future perspectives on additional studies that need to be conducted to understand the auxin pathway better and to use the findings to improve maize architecture.