HASTY: a gene that regulates the timing of shoot maturation in Arabidopsis thaliana.

In Arabidopsis thaliana, leaves produced at different stages of shoot development can be distinguished by the distribution of trichomes on the abaxial and adaxial surfaces. Leaves produced early in the development of the rosette (juvenile leaves) have trichomes on their adaxial, but not their abaxial surface, whereas leaves produced later in rosette development (adult leaves) have trichomes on both surfaces. In order to identify genes that regulate the transition between these developmental phases we screened for mutations that accelerate the production of leaves with abaxial trichomes. 9 alleles of the HASTY gene were recovered in this screen. In addition to accelerating the appearance of adult leaves these mutations also accelerate the loss of adaxial trichomes (a trait typical of bracts), reduce the total number of leaves produced by the shoot, and have a number of other effects on shoot morphology. The basis for this phenotype was examined by testing the interaction between hasty and genes that affect flowering time (35S::LEAFY, 35S::APETALA1, terminal flower1), gibberellin production (ga1-3) or perception (gai), and floral morphogenesis (leafy, apetala1, agamous). We found that hasty increased the reproductive competence of the shoot, and that its does not require gibberellin or a gibberellin response for its effect on vegetative or reproductive development. The phenotype of hasty is not suppressed by leafy, apetala1 and agamous, demonstrating that this phenotype does not result from the inappropriate expression of these genes. We suggest that HASTY promotes a juvenile pattern of vegetative development and inhibits flowering by reducing the competence of the shoot to respond to LEAFY and APETALA1.