Intracellular pH sensing is altered by plasma membrane PIP aquaporin co-expression

JORGE BELLATI; KARINA ALLEVA; GABRIELA SOTO; VICTORIA VITALI; MOIRA SUTKA; GABRIELA AMODEO

Buzios, Rio de Janeiro, Brasil

Congreso; VII Iberoamerican Congress of Biophysics; 2009

SOCIEDAD BRASILEÑA DE BIOFISCA- SOBLA- SOCIEDAD ARGENTINA DE BIOFISICA

Objectives: The plant plasma membrane barrier can express aquaporins (PIP1 and PIP2) that show two intriguing aspects: i) the potential of modulating whole membrane water permeability by co-expression of both types, recently been distinguished for showing a differential capacity to reach the plasma membrane (Plant Cell 16:215-28, 2004); and ii), the faculty to reduce water permeation through the pore after cytoplasmic acidification (Nature. 425:393-7, 2003), as a consequence of a gating process. We therefore decided to test if these two key features might enhance plasticity to the membrane water transport capacity if they jointly trigger any cooperative interaction. Methods: We proved by biophysical approaches that the plasma membrane of the halophyte Beta vulgaris storage root present highly permeable aquaporins that can be shut down by acidic pH (J Exp Bot. 57:609-21, 2006). We therefore took advantage of this preparation to subclone three root Beta vulgaris PIPs (BvPIP1;1, BvPIP2;1 and BvPIP2;2) and achieve their functional characterization by the expression or co-expression of their cRNA in a heterologous system (Xenopus oocytes). Results: Co-expression of BvPIP1;1 and BvPIP2;2 not only enhance oocyte plasma membrane water permeability synergistically showing a sevenfold increment but also reinforces pH inhibitory response from partial (75%) to a complete shut down (99%), when lowering cytoplasmic pH to 6.0. This pH dependent behavior shows that PIP1-PIP2 co-expression accounts for a different pH sensitivity by shifting the inhibitory response in almost one pH unit (EC50 pH 6.1 to pH 6.9) compared to BvPIP2;2 expressed alone. Conclusion: These results show for the first time that PIP co-expression impacts modulating the membrane water permeability through a pH regulatory response, enhancing in this way membrane versatility to adjust its water transfer capacity.