Heterochronic effects of glossy15 mutations on epidermal cell identity in maize

Vegetative development in maize is divided into a juvenile phase and an adult phase that differ in the expression of a large number of morphological, anatomical, and biochemical traits. Recessive mutations of Glossy15 cause a premature switch in the expression of some of these phase-specific traits. Mutant plants cease producing juvenile traits (e.g. epicuticular wax) and begin to produce adult traits (e.g. epidermal hairs) significantly earlier than their wild-type siblings. In glossy15-1 plants this switch generally occurs at leaf 2 or 3 rather than at the normal position of leaf 6 or 7. An analysis of the effect of glossy15 mutations on a variety of vegetative and reproductive traits revealed that these mutations only affect the character of the epidermis. They have no effect on the overall vegetative morphology of the plant, or on its reproductive development. This phenotype is the opposite of that of the gain-of-function mutations Teopod1, Teopod2 and Teopod3, all of which prolong the expression of a large number of juvenile traits. Double mutants between glossy15 and Teopod1 or Teopod2 indicate that Glossy15 is required for the effect of Teopod1 and Teopod2 on epidermal traits but not for other aspects of the Teopod phenotype. We conclude that Glossy15 initiates or maintains the expression of juvenile epidermal traits and suppresses the expression of adult epidermal traits, and that it acts downstream of the Teopod genes.