Addressing the plant phyllotaxis problem using modeling and in vivo live imaging

Henrik Jönsson , M. Heisler, G. Venugopala Reddy, B. E. Shapiro, V. Gor, E. M. Meyerowitz, E. Mjolsness

Department of Theoretical Physics Lund University

The shoot apical meristem (SAM) in plants is an amazing dynamical system that provides a basis for the development of the complete aboveground part of the plant. It contains a constant pool of stem cells throughout the life of the plant, and although individual cells differentiate and move away from the shoot apex, spatial regions of gene expression stay constant within the SAM. At the periphery of the SAM new organs, such as leaves and flowers, are constantly formed in a remarkably regular pattern. This pattern is called phyllotaxis and the question of how it originates has inspired theoretical scientists for hundreds of years, partly due to its connection to the Fibonacci series. It has recently been shown that polarized transport of the molecule auxin mediated by PINFORMED proteins are essential for this process. We are applying an approach where in vivo live imaging of proteins and cells is used together with modeling to gain a better understanding of molecular processes within the SAM. The in vivo imaging technique, where proteins are fused to GFP, is used for dynamical tracking of the subcellular locations of important proteins throughout the complete SAM for a time period of days. In parallel we are developing software for simulation of developmental multicellular systems where the Arabidopsis SAM is used as the main biological target. The software allows for the simulation of gene regulatory networks, molecular reactions, molecular transport between cells, cell growth and division, and mechanical interactions between cells. In this talk I will describe models for the phyllotaxis problem. The models are built on new biological data, and various simulation results will be presented along with analysis of the models.

Miscellaneous HJ is in part supported by the Knut and Alice Wallenberg Foundation through Swegene. Additional support provided by NSF:FIBR award number EF-0330786