Genetic regulation of vegetative maturation in maize

During development higher organisms pass through a series of phases. In plants the duration of these phases has a direct impact on the morphology of the plant because organs produced at different times in development are located at different positions along the shoot. Vegetative development in maize is divided into a juvenile phase and an adult phase that differ in the expression of many morphological, anatomical, and biochemical traits. The juvenile, or basal, part of the shoot posseses axillary roots, tillers, and leaves that have a number of distinctive traits, the most obvious of which are the production of a visible form of epicuticular wax and the absence of visible hairs. The adult part of the shoot lacks prop roots and possesses pubescent leaves that lack visible epicuticular wax. Vegetative maturation, the transition between these phases, requires the termination of expression of juvenile traits and the onset of expression of adult traits. These two processes may be regulated in an independent or coordinate fashion. By identifying and examining the expression of markers for both of these phases, zebra banded4 and Jul1 for the juvenile and Ragged leaves1 for the adult, in different mutant backgrounds, I have demonstrated that these two processes can be linked to one another but are affected unequally by most of the known heterochronic mutations. The Teopod and dwarf mutations prolong the expression of juvenile traits and slightly delay the expression of adult traits. The viviparous8 mutation, in contrast, prolongs juvenile development and delays adult development equally. All of these mutations require a functional Glossy15 gene to prolong the expression of juvenile epidermal traits. glossy15 mutations cause a premature shift from juvenile to adult epidermal traits. The Teopod, dwarf, and viviparous8 mutations interact in a synergistic fashion to prolong juvenile development suggesting that vegetative maturation is regulated by the interaction of many independent factors. Although the two vegetative phases of shoot development are frequently regulated independently, their expression suggests that they interact with one another in a combinatorial fashion to specify the identity of the shoot