Characterization of root plasma membrane aquaporins from the halophyte storage root Beta vulgari

ALLEVA, KARINA; SOTO, GABRIELA; MUT, PAULA; MUSCHIETTI, JORGE; AMODEO, GABRIELA

Boston, EEUU;

Congreso; ASPB Meeting en Agosto 2006.; 2006

AMERICAN SOCIETY OF PLANT BIOLOGISTS

Root plasma membrane aquaporins (PIPs) can be modulated by short-term regulatory mechanisms that directly affect channel gating. In particular, the activity of PIPs present in the halophyte Beta vulgaris storage root shows sensitivity to both cytosolic acidification and calcium (Alleva et al., 2006). Western blot analysis confirmed the presence of at least PIP1 and PIP2 subgroup in an enriched fraction of plasma membrane vesicles from this root. To complement these studies a full-length cDNA (named BvPIP2) was isolated from Beta vulgaris root using specific primers according to Qi et al., 1996. The phylogenetic analysis of its deduced amino acid sequence confirms that the corresponding protein has high homology with an Atriplex PIP (90%), a SoPIP2 (87%) and AtPIP2.8 (86%). Although the PIP2 subgroup is one of the best described in the literature, the mentioned homologues have been barely studied in terms of their functionality. BvPIP2 sequence shows the conserved His residues responsible of pH sensitivity as reported in AtPIPs as well as intraloop phosphorylation sites. Experiments performed expressing BvPIP2 in a heterologous system (Xenopus oocytes) show water permeability values of 25.3 ± 8.8 cm.s-1 for BvPIP2 compared to 97.0±24.8 for AtPIP2.3 (positive control) and 7.6±2.4 for water (negative control) injected oocytes. Interestingly, these results point that BvPIP2 has a lower water permeability profile in contrast with the already described PIP2.