Poster: Hormones

Abs # 642: Altered auxin distribution in atmdr1-1analyzed by DR5::GUS expression

Presenter:	Lewis, Daniel R, drlewis2@wisc.edu
Authors	Lewis, Daniel R (A)   Noh, Bosl  (A)   Spalding, Edgar P (A)
Affiliations:	(A): University of Wisconsin department of Botany

Polar auxin transport (PAT) is defined as the basipetal movement of auxin from its site of synthesis in the apex to zones of accumulation. This biased transport is facilitated by the basal localization of an efflux carrier complex containing PIN1. The ATMDR1 ABC transporter is necessary for normal levels of PAT. The T-DNA insertional mutant atmdr1-1 only shows 15% of wild type levels. This mutation abolishes the basal localization of PIN1 which could explain the phenotype. In order to probe the effect of the atmdr1-1 mutation on auxin distribution we performed visual measurements of the auxin responsive promoter DR5 fused to GUS. atmdr1-1 cotyledons appeared faintly stained compared to the wild type. This result indicated that either polar transport from the apex to the cotyledons through the petiole is disrupted in the mutant or that the auxin sensitivity in the atmdr1-1 cotyledons was lower. A dose-response analysis was employed to determine the sensitivity of the tissue to exogenous auxin. The flourogenic substrate MUG, combined with a fluorescence plate reader enabled quantitative assessment of DR5::GUS activity. This activity was induced by treating the mutant and wild-type with different concentrations of auxin ranging from .05-50 mM. The similar inducibility indicated that the mutation did not affect auxin sensitivity. Based on this result it was concluded that the monitoring of auxin content via DR5::GUS in cotyledons is a valid PAT assay. This procedure provides a tool to examine the mechanism of PAT and its dependence on proper PIN1 localization by testing various deficiencies and control elements for their effect on the system. These include not only the atmdr1-1 mutation, but also a large class of proposed synthetic and endogenous regulators.