UC Riverside

Organ boundaries serve several important roles in development, but the mechanisms downstream of boundary-defining factors are not well understood. In Chapter 1 of my dissertation, I show the Arabidopsis transcription factor LOB regulates leaf angle via a phototropism-dependent mechanism, reducing phototropic responses at the base of the leaf. LOB and other boundary-defining transcription factors also regulate numerous cell wall genes, implying a biophysical mechanism is an important aspect of boundary function. Given the inherent challenges of measuring cell wall mechanics in the Arabidopsis leaf-meristem boundary, I used a different system, the maize ligular region, which is highly amenable to AFM experiments. In Chapter 2, I characterized mechanical patterns during the development of the ligular region. My findings are consistent with the existence of a cell wall rigidification program in the boundary, which correlates with patterns of growth, cell division, and auxin dynamics. In Chapter 3, I measured epidermal cell geometry and cell wall stiffness over a wide area of the maize leaf. I found that the establishment of the boundary in the maize leaf was linked not just to local changes, but to broader growth and mechanical patterns outside the boundary. This suggests that coordination between the boundary and adjacent leaf zones is involved in the morphogenesis of the maize leaf. My findings further our understanding of how plant boundaries regulate growth.