Poster: Membrane Transport

Abs # 1221: Heavy metal ATPases in Arabidopsis thaliana

Presenter:	Williams, Lorraine E, lew@soton.ac.uk
Authors	Williams, Lorraine E (A)   Mills, Rebecca F (A)   Krijger, Gerard C (B) (A)  Baccarini, Paul J (A)   Hall, John L (A)
Affiliations:	(A): University of Southampton (B): Delft University of Technology
Web Site:	http://www.sbs.soton.ac.uk/staff/lew/lew.htm

CPx-ATPases or heavy metal P-type ATPases (HMAs) transport cations such as Zn, Cu, Cd, Pb, and Ag in a wide range of organisms (Williams et al. 2000, BBA 1465, 104-126). They are a sub-group of the P-type ATPase superfamily and functions include delivering essential metals to target enzymes, mediating resistance to non-essential cations or alleviating effects of toxic concentrations of essential cations. Arabidopsis thaliana contains eight HMAs in its genome (AtRAN1/AtHMA7, AtPAA1/AtHMA6 and AtHMA1-5 and 8). We have focussed our studies on AtHMA1 and 4. Sequencing showed that these pumps have the conserved motifs found in all P-type ATPases. AtHMA4 also contains typical motifs of the CPx-ATPase sub-class including the characteristic CPC motif in the predicted sixth transmembrane domain and the HP locus in the predicted large cytoplasmic loop. AtHMA1 contains the HP locus but instead of a characteristic CPx motif, it contains an SPC motif. A small sub-group of HMAs from other organisms also contain this sequence difference and these also cluster separately in phylogenetic analysis. The functional significance of this difference is not known but interestingly AtHMA1 and HMA4 have quite different effects when heterologously expressed in yeast with respect to Cd tolerance. In addition, these pumps differ slightly in their organ expression pattern and in their response to different metals, indicating that they may have different physiological roles in Arabidopsis thaliana. The cloning and characterization of AtHMA1 and AtHMA4 will be presented and their possible functions discussed.