Functional analyses of initiation and laminar expansion of plant lateral organs.

Plants are comprised of a series of repeated lateral organ segments that develop from small clumps of morphogenic tissue called shoot meristems. The leaf is a ground state lateral organ; the developmental mechanisms generating leaves are repeated and modified during development of inflorescences and flowers. Thus, an understanding of leaf development is central to our comprehension of overall plant development. Previous molecular genetic analyses in diverse plant species have generated testable models for mechanisms of leaf initiation and growth. In addition, comparative approaches are important toward understanding how diverse leaf morphology has evolved, and may be modified for agronomic advantage in the future. This research exploits recessive mutations that affect the initiation and/or expansion of leaves. Experiments are ongoing to investigate the expression patterns and functions of these genes, and to understand the development and morphological evolution of leaves. Three specific aims are underway.

1. The maize/Arabidopsis genes NARROW SHEATH (NS)/PRESSED FLOWER (PRS) are required for the initiation of lateral leaf domains from shoot meristems. Maize and Arabidopsis leaves are simple, whereas tomato forms compound leaves comprised of many leaflets. In collaboration with the Dr. Neelima Sinha lab at UC Davis, the NS/PRS gene is cloned from tomato, and molecular-genetic analyses will determine the function of this gene during the development of compound tomato leaves.
2. The developmental timing and meristematic tissue layer-specificity of PRS accumulation and function is being analyzed with fluorescently tagged proteins and specific antibodies. These experiments will investigate mechanisms of PRS non-cell autonomy, wherein PRS functions beyond those cells and tissues in which PRS is expressed.
3. Map-based cloning techniques are underway to identify the RAGGEDSEEDLING gene, and analyses of RGD2 expression during maize development will generate models for how RGD2 functions during the lateral growth and expansion of leaves.

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