Regulation of maize aquaporin trafficking to the plasma membrane
(2008)
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- Authors
- Supervisors
- Chaumont, François
- Abstract
- Maize plasma membrane aquaporins (ZmPIPs) fall into two groups, ZmPIP1s and ZmPIP2s, that exhibit different water channel activities when expressed in Xenopus oocytes. For instance, ZmPIP1;1 and ZmPIP1;2 are inactive, whereas ZmPIP2;1, ZmPIP2;4 and ZmPIP2;5 induce a marked increase in the membrane osmotic water permeability coefficient, Pf. A previous study showed that, in Xenopus oocytes, ZmPIP1;2 and ZmPIP2;1 interact to increase the cell Pf. In this thesis, we report the localization and interaction of ZmPIP1s and ZmPIP2s in living maize cells. ZmPIP proteins were fused to monomeric Yellow or Cyan Fluorescent Protein (mYFP and mCFP) and expressed transiently in maize mesophyll protoplasts. When expressed alone, ZmPIP1 fusion proteins were retained in the endoplasmic reticulum (ER), whereas ZmPIP2s were found in the plasma membrane. Interestingly, when co-expressed with ZmPIP2s, ZmPIP1s were relocalized to the plasma membrane. Using Förster resonance energy transfer-fluorescence lifetime imaging microscopy, we demonstrated that this relocalization resulted from interaction between ZmPIP1s and ZmPIP2s. Immunoprecipitation experiments provided additional evidence for the association of ZmPIP1;2 and ZmPIP2;1 in maize roots and cultured cells. These data suggest that, in maize cells, hetero-oligomerization of ZmPIP1s and ZmPIP2s is required for trafficking of the former to the plasma membrane to modulate plasma membrane permeability. To determine the domains responsible for the ER retention and plasma membrane localization of ZmPIP1s and ZmPIP2s, respectively, truncated and mutated ZmPIP proteins were generated together with chimeric proteins created by swapping ZmPIP2 and ZmPIP1 regions. These mutated proteins were fused to the mYFP and/or mCFP, expressed in protoplasts and localized by microscopy. We identified a diacidic motif, DIE, in position 4-6 of the N-terminus of ZmPIP2;5 that was essential for the ER export. This motif was conserved and functional in ZmPIP2;4 but absent in ZmPIP2;1. In addition, we showed that ZmPIP2;5 N-terminus was not sufficient to export ZmPIP1;2 from the ER. The study of ZmPIP1;2 mutants suggested that the N- and C-termini of this protein were probably not involved in ER retention. Altogether, these results show that the surface expression of maize plasma membrane aquaporins is differently regulated according to the isoforms and involved specific signals and/or formation of hetero-oligomers.
- Affiliations
Citations
Zelazny, E. (2008). Regulation of maize aquaporin trafficking to the plasma membrane. https://hdl.handle.net/2078.5/124105