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 t he abaxial and adaxial surfaces. Leaves produced early in the developm ent of the rosette (juvenile leaves) have trichomes on their adaxial, but not their abaxial surface, whereas leaves produced later in rosett e development (adult leaves) have trichomes on both surfaces. In order to identify genes that regulate the transition between these developm ental phases we screened for mutations that accelerate the production of leaves with abaxial trichomes, 9 alleles of the HASTY gene were rec overed in this screen. In addition to accelerating the appearance of a dult leaves these mutations also accelerate the loss of adaxial tricho mes (a trait typical of bracts), reduce the total number of leaves pro duced by the shoot, and have a number of other effects on shoot morpho logy, The basis for this phenotype was examined by testing the interac tion between hasty and genes that affect flowering time (35S::LEAFY, 3 5S::APETALA1, terminal flower1), gibberellin production (ga1-3) or per ception (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 fa r its effect on vegetative or reproductive development, The phenotype of hasty is not suppressed by leafy, apetala1 and agamous, demonstrati ng that this phenotype does not result from the inappropriate expressi on of these genes. We suggest that HASTY promotes a juvenile pattern o f vegetative development and inhibits flowering by reducing the compet ence of the shoot to respond to LEAFY and APETALA1.