Poster: Vegetative development

Abs # 330: MDR-like genes in arabidopsis involved in auxin transport and auxin-mediated development

Presenter:	Lewis, Daniel R., drlewis2@students.wisc.edu
Authors	Lewis, Daniel R. (A)   Noh, Bosl  (B)   Spalding, Edgar P (A)
Affiliations:	(A): University Of Wisconsin (B): Korea Kumho Petrochemical Co.

The polar transport of auxin through arabidopsis aerial tissue is facilitated by the asymetric localization of an efflux carrier complex containing AtPIN1. The AtMDR1 ABC transporter has been implicated in the control of this localization. A T-DNA insertional mutant, atmdr1-1 shows an 85% reduction in basipetal hypocotyl auxin transport. This mutation also disrupts the basal localization of PIN1, leading to a uniform distribution of the presumptive efflux carrier. In order to probe the effect of the mdr1-1 mutation on auxin distribution, we performed visual measurements of the auxin responsive promoter DR5 fused to GUS. Cotyledons of mdr1-1 were delayed in enlargement, epinastic, and appeared faintly stained compared to the wild type. A dose-response analysis, carried out with the DR5::GUS auxin responsive reporter, demonstrated that the sensitivity of the tissue to exogenous auxin was normal. This result indicated that these phenotypes were due to a transport defect. To test the hypothesis that auxin transport from the apex through the petiole was perturbed in mdr1-1, cotyledons were excised and fixed on a support with their petioles submerged in a solution containing 2μM IAA. The endogenous (control) DR5 signal was then quantified. The import of auxin was then measured by subtracting the endogenous DR5 signal from the experimental treatment and dividing by the length of the treatment. The results from this assay suggest that the cotyledon phenotypes observed in mdr1-1 (epinasty, delayed enlargement, delayed or reduced DR5 signal) are most likely due to a decrease in polarized transport through the petiole to the developing embryonic leaf. Additional reverse genetic studies of other AtMDR family members are ongoing and will also be discussed.