| Unable to move and possessing relatively long life-spans, plants are subject to diverse internal and external challenges that can result in the loss or wearing down of body parts. Regeneration is one strategy used to repair the body plan, invoking mechanisms that can restore partially missing or damaged body parts or create entirely new organs or complete body plans, often in an ectopic location. In the Arabidopsis root, severing of the distal-most region, including removal of the underlying growth center (stem-cell niche), triggers a rapid regeneration program in which morphology, distal fates, and function are restored within days in the absence of any exogenous treatment. While some of the major events and factors governing this process have been characterized, two key features remain unresolved: 1) Which differentiated tissue types (files) in the damaged structure contribute to the restored organ? 2) What factors guide re-patterning to ensure appropriate restoration of tissue fates and organizations?;To address these fundamental questions, I adapted classic lineage-marking techniques for use in the Arabidopsis root and combined these new tools with high-resolution, time-course imaging. Tracing the recruitment and contribution of "old" tissue to "new" files reveals that contrary to many characterized modes of regeneration in plants and animals, multiple tissue types are recruited to the regenerating root tip; furthermore, the contributions of these files are highly constrained and influenced by position, rather than origin identity in the damaged organ. Additional work characterizing the regeneration dynamics of distal fate markers and key, position-dependent candidate patterning factors have not only allowed us to gain insight into the natural competency of distal root cells, but also to construct a refined positional and temporal fate map for root tip regeneration that serves as a basis for future studies in this system.;Part II of this thesis discusses the development and implementation of genomic techniques, resources, and other tools to advance research in the evolutionarily significant system, Selaginella. Detailed are essential laboratory techniques for S. moellendorffii, including propagation, tissue culture generation and maintenance, means of transient transformation, and working approaches to generate RNAseq libraries from difficult to obtain, low-input samples in this system. Also included are characterizations of root development and plasticity in this system. Taken together, the work described here not only provides a characterization root organs and identity in this emerging model but also makes this important early land plant system more accessible to the larger research community. |
