title: Hormonal networks involved in apical hook development in darkness and their response to light.
abstract: In darkness, the dicot seedlings produce an apical hook as result of differential cell division and extension at opposite sides of the hypocotyl. This hook protects the apical meristem from mechanical damage during seedling emergence from the soil. In darkness, gibberellins act via the DELLA-PIF (PHYTOCHROME INTERACTING FACTORs) pathway, and ethylene acts via the EIN3/EIL1 (ETHYLENE INSENSITIVE 3/EIN3 like 1)-HLS1 (HOOKLESS 1) pathway to control the asymmetric accumulation of auxin required for apical hook formation and maintenance. These core pathways form a network with multiple points of connection. Light perception by phytochromes and cryptochromes reduces the activity of PIFs and (COP1) CONSTITUTIVE PHOTOMORPHOGENIC 1-both required for hook formation in darkness-, lowers the levels of gibberellins, and triggers hook opening as a component of the switch between heterotrophic and photoautotrophic development. Apical hook opening is thus a suitable model to study the convergence of endogenous and exogenous signals on the control of cell division and cell growth.
authors.affiliation: Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, "Dr. Héctor Torres" (INGEBI-CONICET) Buenos Aires, Argentina.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Mazzella
authors.affiliation: Facultad de Agronomía, Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura, Universidad de Buenos Aires and CONICET Buenos Aires, Argentina ; Fundación Instituto Leloir, Instituto de Investigaciones Bioquímicas de Buenos Aires-CONICET Buenos Aires, Argentina.
authors.forename: Jorge J
authors.initials: JJ
authors.lastname: Casal
authors.affiliation: Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, "Dr. Héctor Torres" (INGEBI-CONICET) Buenos Aires, Argentina ; Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires Buenos Aires, Argentina.
authors.forename: Jorge P
authors.initials: JP
authors.lastname: Muschietti
authors.affiliation: Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, "Dr. Héctor Torres" (INGEBI-CONICET) Buenos Aires, Argentina.
authors.forename: Ana R
authors.initials: AR
authors.lastname: Fox
keywords: Arabidopsis; COP1; PIFs; apical hook; auxin; ethylene; gibberellins; photoreceptors