Dorsiventrality and developmental patterning of maize leaves
Henderson, David Clark
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Although molecular biology has revealed various players in the game of leaf development we continue to have only a crude understanding of how the players interact and what, exactly, it is that they do. A problem in plant development common to many organisms is the acquisition of new developmental axes. The puzzle of acquiring a new developmental axis is central to early leaf development, as the shoot apical meristem must somehow instruct a population of cells to grow away from the plant body and form the flat, planar structure of the leaf. Current models give prime importance to the adaxial/abaxial pattern of the leaf in providing the axis necessary for planar growth. In this study I take a molecular genetic approach to add to the current model of leaf development. --The Ragged seedling2 (Rgd2) mutant of maize is defective in mediolateral and adaxial/abaxial patterning. Rgd2 morphology is similar to that of other adaxial/abaxial patterning mutants but Rgd2has peculiarities that provide fresh questioning and exploration of leaf development. In this study I thoroughly characterize Rgd2morphology and anatomy, on the gross and fine scales. A characterization of defects in molecular patterning of the shoot apical meristem and leaf primordia is performed. A model for RGD2 function is proposed based primarily on KNOX protein accumulation data and observations of anatomical defects. The model is tested using expression of Rolled1-O and of a maize KANADI homologue, a first for monocots. Double mutant -analyses are also performed with relevant patterning mutants, Narrow sheath, the --dominant Rolled1-OD, and Lbl1-rgd1. These test lead to a revision of the model which places RGD2 function early in leaf development in a process of enhancing or maintaining expression of adaxial/abaxial organizers. The cloning of RGD2 is also discussed; various cloning strategies are outlined and details of progress toward cloning RGD2 are provided.