During its growth the maize shoot progresses through distinct juvenile and adult phases of vegetative growth and then enters a reproductive phase. Previous work has suggested that these three phases are regulated by independent, but interacting developmental programs. The extent of coordination between these programs will be tested by studying the effect of "early flowering" genes on phase-specific vegetative traits, and by examining the interaction between these genes and several mutations that cause the constitutive expression of a juvenile vegetative program (Tp1, Tp2 and Tp3). To obtain a more complete picture of the genetic regulation of phase change, several recently identified mutations that affect the expression of phase specific vegetative traits will be characterized at a cellular and molecular level. Other genes that regulate phase change will be identified by screening for suppressors of Tp2, and by screening for mutations that cause the precocious expression of adult vegetative traits. Finally, g115, a gene that regulates several juvenile traits, will be cloned by transposon-tagging.
