title: A hormonal regulatory module that provides flexibility to tropic responses.
abstract: Plants orient their growth depending on directional stimuli such as light and gravity, in a process known as tropic response. Tropisms result from asymmetrical accumulation of auxin across the responding organ relative to the direction of the stimulus, which causes differential growth rates on both sides of the organ. Here, we show that gibberellins (GAs) attenuate the gravitropic reorientation of stimulated hypocotyls of dark-grown Arabidopsis (Arabidopsis thaliana) seedlings. We show that the modulation occurs through induction of the expression of the negative regulator of auxin signaling INDOLE-3-ACETIC ACID INDUCIBLE19/MASSUGU2. The biological significance of this regulatory mechanism involving GAs and auxin seems to be the maintenance of a high degree of flexibility in tropic responses. This notion is further supported by observations that GA-deficient seedlings showed a much lower variance in the response to gravity compared to wild-type seedlings and that the attenuation of gravitropism by GAs resulted in an increased phototropic response. This suggests that the interplay between auxin and GAs may be particularly important for plant orientation under competing tropic stimuli.
authors.affiliation: Instituto de Biología Molecular y Celular de Plantas, 46022 Valencia, Spain.
authors.forename: Javier
authors.initials: J
authors.lastname: Gallego-Bartolomé
authors.forename: Chitose
authors.initials: C
authors.lastname: Kami
authors.forename: Christian
authors.initials: C
authors.lastname: Fankhauser
authors.forename: David
authors.initials: D
authors.lastname: Alabadí
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Blázquez
mesh_terms: D017360:Arabidopsis / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005875:Gibberellins / Q000494:pharmacology*; D018522:Gravitropism / Q000187:drug effects* / Q000502:physiology*; D018546:Hypocotyl / Q000187:drug effects / Q000502:physiology; D009154:Mutation / Q000235:genetics; D012097:Repressor Proteins / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D005875:Gibberellins; D012097:Repressor Proteins; C007842:gibberellic acid