Symposium V: The Plasma Membrane: A Happening Place

Abs # 50001: Functional genomics of gene families of P-type pumps in Arabidopsis

Presenter:	Palmgren, Michael P., palmgren@biobase.dk
Authors	Palmgren, Michael P. (A)   Romanowsky, Shawn  (B)   Jakobsen, Mia K. (A)   Schiott, Morten  (A)   Sondergaard, Teis  (A)   Baekgaard, Lone  (A)   Fuglsang, Anja T. (A)   Schulz, Alexander  (A)   Amtmann, Anna  (C)   Harper, Jeffrey F. (B)
Affiliations:	(A): Plant Physiology and Anatomy Laboratory, Department of Plant Biology, The Royal Veterinary and Agricultural University, Copenhagen, Denmark (B): Department of Cell Biology, Plant Division, The Scripps Research Institute, La Jolla, CA 92037, IBLS (C): Bower Building, University of Glasgow, Glasgow G12 8QQ, United Kingdom
Web Site:	http://www.trap.kvl.dk

P-type ATPases are biological pumps involved in the active transport of a variety of cations out of the cytoplasm. In Arabidopsis thaliana, P-type ATPases are encoded by a gene family of 46 members that forms five distinct gene clusters, P1 – P5. T-DNA knockout mutants have been isolated for most of the Arabidopsis P-type pumps and provide an avenue for understanding their physiological roles.

Ca²⁺ is an intracellular messenger involved in plant growth and development. Among the closely related Ca²⁺-ATPase isoforms ACA8 – ACA10 (P2B ATPases), ACA8 is expressed in the plasma membrane. Homozygous aca9 plants have shorter siliques and reduced amount of seeds compared to wild-type plants. The reduced seed set in aca9 plants is caused by partial male sterility resulting from i) impaired pollen tube growth and ii) a defect in the fertilization event. This provides genetic evidence for an important role of a specific calcium transporter in these processes.

A proton gradient across the plasma membrane is crucial for the ability of plants to take up nutrients. P-type plasma membrane H⁺-ATPases (P3 ATPases) constitute a gene family in all plants. A number of protein kinases phosphorylate the C-terminal regulatory domain at multiple sites. Among these, a receptor-like protein kinase, PIRK1, interacts with and phosphorylates the C-terminal H⁺-ATPase autoinhibitor in vitro. A pirk1 knock-out mutant has an auxin-related phenotype suggesting a possible link between auxin action and activation of proton transport across the plasma membrane.

P5 ATPases are present in all eukaryotes examined so far but the physiological role and biochemical function of these proteins are poorly understood. A knockout mutant of the single gene POW1 belonging to this subfamily in Arabidopsis has been characterized. Mutant plants are male sterile and pollen grains stick together, are deformed or collapsed. DNA microarray analysis revealed that expression of a large number of genes involved in cell wall modification is changed in pow1. These observations suggests an important role for POW1p in formation of the plant cell wall.