Poster: Membrane transport
Abs #
169: Regulation of plasma membrane aquaporins from maize
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Presenter: |
Van Wilder, Valerie , vanwilder@fysa.ucl.ac.be |
Authors | Van Wilder, Valerie (A) Degand, Herve (A) Chaumont, Francois (A) | | Affiliations: |
(A): Universite catholique de Louvain
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The osmotic water permeability of the cell membranes is dependent on the presence of active aquaporins. We are investigating the mechanisms regulating the plasma membrane aquaporin (PIP). The water channel activity is mostly derived from experiments with Xenopus oocytes. Cells expressing an aquaporin swell more rapidly in hypo-osmotic medium than control cells.
Using this system, we showed that co-expression of the non-functional ZmPIP1;2 and functional ZmPIP2;1, ZmPIP2;4, or ZmPIP2;5 resulted in an increase in Pf which was dependent on the amount of injected ZmPIP1;2 cRNA. Confocal analysis of oocytes expressing ZmPIP1;2-GFP alone or ZmPIP1;2-GFP plus ZmPIP2;5 showed that the amount of ZmPIP1;2-GFP present in the plasma membrane was significantly higher in co-expressing cells. Physical interaction of ZmPIP1;2-GFP and ZmPIP2;1 fused to a His tag was demonstrated by affinity chromatography (Fetter et al. (2004) Plant Cell 16, 215). This data revealed a new mechanism of plant aquaporin regulation.
We also showed that plasma membrane PIPs from etiolated maize shoots were in vivo and in vitro phosphorylated. This phosphorylation occurred on a serine residue and was due to a Ca-dependent kinase associated with the plasma membrane. Three PIP2 isoforms (ZmPIP2;1, ZmPIP2;3 and ZmPIP2;4) were detected in the phosphorylated band. The water channel activity of these isoforms was partially inhibited by H7, a PKC inhibitor, suggesting an important effect of phosphorylation on channel function. The two predicted phosphorylation sites of ZmPIP2;1 have been mutagenized (S126A, S285A, S126E and S285E) and the mutants tested in oocytes. A decrease of the water channel activity of ZmPIP2;1S126A was observed. We are currently investigating the role of the phosphorylation in plant cells.
