The objective of this research is to understand the genetic mechanisms whereby leaves formed at different times in vegetative development acquire the specific traits that distinguish them. Toward this end, the differences between the first leaves formed during development(juvenile leaves) and those formed later (adult leaves) will be carefully catalogued and marker genes that distinguish juvenile and adult leaves will be identified. Mutants that specifically affect the appearance or the timing of adult trichomes and epicuticular waxes, such as early trichomes (ert) in Arabidopsis and glossy15(gl15) in maize, will be used as a starting point to identify other mutants that affect the process of vegetative phase change. The function of ert will be probed by examining its expression pattern and cellular localization in normal and mutant plants, by over-expressing the cDNA in transgenic plants, and by identifying unlinked enhancers and suppressors. The conservation of regulation of leaf identity will be investigated by testing for phenotypic effects of the maize GL15 protein in Arbidopsis. Should the effects of the maize gene indicate a possible role for GL15 in Arabidopsis leaf identity, GL15-like sequences will be characterized. Molecular marker genes specific for juvenile and adult leaves will be identified using differential display reverse transcription PCR and the paused mutants that behaves as a specific deletion of the first few juvenile leaves. The traits, mutants, and genes identified in this manner will provide our first glimpse into the molecular mechanism by which vegetative leaf identity is established and will provide tools for dissecting the regulation of vegetative phase change in plants.
