Strawberry PIP regulation by membrane tension increments may have a cooperative mechanism ruled by homo-or heterotetramerization

GUASTAFERRI, FLORENCIA V.; CAVIGLIA, AGUSTÍN F.; GIBSON, OLIVER M.; SUTKA, MOIRA; GALIZIA, LUCIANO; OZU, MARCELO

Congreso; RAFV Conference 2021 - XXXIII Argentinian meeting of Plant Physiology; 2021

FaPIP1;1 and FaPIP2;1 areaquaporins from Fragaria x ananassa that modulate plasma membrane (PM) waterpermeability (Pf) during strawberry ripening. FaPIP2;1 promotes highmembrane Pf when expressed in Xenopus laevis oocytes andreduces its water transport capacity under cytosolic acidification. When FaPIP2;1is coexpressed with FaPIP1;1, both PIPs form heterotetramers and exhibit an enhancedpH gating sensitivity. This shows that interactions between different subunitsmodify the cooperativity among monomers, so we propose that FaPIP2;1-FaPIP1;1heterotetramers are a suitable model to study the cooperativity in mechanicalregulation of aquaporins. In the current work we studied the osmotic behaviorof Xenopus oocytes expressing FaPIP2;1 alone or together with FaPIP1;1.Our aim was to evaluate FaPIP2 homotetramers and FaPIP2-FaPIP1 heterotetramersresponse to membrane tension changes, holding the hypothesis that they havedifferent sensitivity to mechanical regulation. By means of osmotic experimentswe found that FaPIP2;1 homotetramers responds just likemechanosensitive aquaporins do, showing low Pf athigh Δosm,whereas FaPIP2;1-FaPIP1;1heterotetramers show the same Pf  at all tested gradients. Simulations performed with a modelthat states that Pf depends on initial permeability and thecell pressure-volume curve, show that the difference between homo- andheterotetramers osmotic responses is due to the regulation mediated by membranetension increments rather than their initial intrinsic permeability. Hence,FaPIP2;1-FaPIP1;1 heterotetramers appear to be at least less sensitive tomembrane tension changes than FaPIP2;1 homotetramers. This suggests that theinteraction between different types of monomers affect the mechanosensitivityof aquaporins evidencing a cooperative effect in the gating mechanism.