Poster: Hormones

Abs # 639: Reduced auxin transport in the brachytic2 (br2) mutant of maize

Presenter:	Blakeslee, Joshua J., blakeslj@purdue.edu
Authors	Blakeslee, Joshua J. (A)   Mutani, D. S. (A)   Briggs, S. P. (A)   Chamberlin, M. A. (A)   Johal, Guri S. (A)   Murphy, Angus S. (A)
Affiliations:	(A): Purdue University

There are over 100 ATP-binding cassette (ABC)-type proteins in the Arabidopsis genome, 53 of which are thought to encode transport proteins. ABC transport proteins have been theorized to transport a variety of substrates including glutathione conjugates, chlorophyll intermediates, and alkaloids. Recently it has been shown that AtMDR1 (AtPGP19) and AtPGP1 mutidrug resistance like P-glycoproteins interact with the auxin transport inhibitor napthylpthalamic acid (NPA). Furthermore, atmdr1 and atpgp1 mutants exhibit defective polar auxin transport, hypertropic hypocotyl bending, and disruption of basal localization of the putative auxin efflux carrier PIN1. It has been shown that AtPGP1 and AtMDR1 interact with the FKBP-like protein Twisted Dwarf1 (TWD1). twd1 is morphologically similar to mdr1 pgp1 double mutants and exhibits similarly reduced auxin transport profiles. Brachytic2 (Br2), a maize ortholog of AtPGP1, has recently been identified as the gene affected in br2 dwarf mutants. Vascular tissue formation in br2 seedlings is disrupted, while seedling roots are more highly branched and are less strictly gravitropic. br2 mutants showed light-dependent, tissue specific defects in auxin transport analogous to those seen in the Arabidopsis pgp1 and mdr1 mutants. Little data is available, however, on the exact mechanism by which MDR proteins function in auxin transport. Potential mechanisms of MDR/PGP function are discussed.