Molecular Genetic Analysis of Phase Change in Maize and Arabidopsis

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Leaves produced during the juvenile and adult phases of shoot development in maize are morphologically, anatomically, and biochemically distinct. Loss-of-function mutations of GLOSSY15 (GL15) cause the epidermis of some juvenile leaves (leaves 3 to 6) to acquire adult characteristics, implying that GL15 normally functions both to promote the expression of juvenile epidermal traits and to repress the expression of adult traits. GL15 is the only gene involved in the regulation of phase-specific differences in leaf morphology that has been cloned. As such, it is useful not only as a molecular marker for phase-specific cell identity in maize, but also as an entry point into the molecular mechanism of this poorly understood phenomenon. The research proposed here will provide the basic information about GL15 necessary for understanding the function of this gene and the way in which its expression is regulated. The expression pattern of GL15 will be examined by in situ analysis of mRNA at different stages of leaf development, and at different stages during the growth of the shoot. This expression analysis will also be conducted on mutations that affect phase change (gef, Tpl, Tp2 and Tp3, dl, vp8) to determine if the effect of these mutations on epidermal identity is mediated by changes in the amount or expression pattern of GL15 mRNA. Other members of this gene family will be cloned, their genomic structure and expression pattern will be characterized, and their function will be determined by isolating Mutator insertions that disrupt their expression. In parallel with this analysis of GL15-1ike genes, Dr. Poethig will conduct a screen for genes that may be functionally redundant with GL15 by screening for mutations that affect the identity of leaves one and two in a gll5-H mutant background. Finally, Dr. Poethig will determine the function of GL15 in Arabidopsis by cloning the orthologue of GL15 in this species and determining its loss-of-function phenotype.