Poster: Hormones

Abs # 631: Functional and spatial analysis of the PM aminopeptidase At APM1 supports a role in membrane targetting

Presenter:	Bandyopadhyay, Anindita , abandyop@purdue.edu
Authors	Bandyopadhyay, Anindita  (A)   Lee, Ok Ran  (A)   Murphy, Angus S (A)   Peer, Wendy A (A)   Makam, Srinivas N (A)   Murphy, Angus S (A)
Affiliations:	(A): Purdue University

Immunohistochemical, enzymatic, and expression studies of AtAPM1, an Arabidopsis homolog of the mammalian Insulin Responsive Aminopeptidase (IRAP), have implicated the protein in the cycling of the putative auxin efflux carrier PIN1 between the plasma membrane and endosomal compartments. New immunohistochemical analyses has revealed dual localization of APM1 to both intracellular vesicles and basal cell membranes. Differential localizations were visible at different developmental stages in the Ws, Col, and Ler ecotypes of Arabidopsis. Expression studies with an APM1-GUS promoter construct revealed colocalization of APM1 with aglycone flavonoids and NPA amidase activities. Mutants lacking flavonoids, natural inhibitors of both auxin transport and AtAPM1 enzymatic activity, have altered localization patterns of APM1 and PIN1. NPA also affects the normal localization pattern of APM and its effects are similar to that of microsomal aminopeptidase inhibitors. Yeast two-hybride analysis suggests that other transport proteins, including a voltage gated anion channel and nitrate transporter, interact with AtAPM1. Mutant analysis of T-DNA insertions in the promoter regions and EMS point mutations in the coding region have been employed to study APM function. A promoter insertion mutant, atapm1-1, has mRNA expression levels <5% of wild type levels and decreased PIN1 localization. Various phenotypes are visible in point mutants. Homozygous null mutants appear to be lethal, indicating that the single copy gene is essential.