CO2 Transport by PIP2 Aquaporins of Barley

Abstract

CO2 permeability of plasma membrane intrinsic protein 2 (PIP2) aquaporins of Hordeum vulgare L. was investigated. Five PIP2 members were heterologously expressed in Xenopus laevis oocytes. CO2 permeability was determined by decrease of cytosolic pH in CO2-enriched buffer using a hydrogen ion-selective microelectrode. HvPIP2;1, HvPIP2;2, HvPIP2;3 and HvPIP2;5 facilitated CO2 transport across the oocyte cell membrane. However, HvPIP2;4 that is highly homologous to HvPIP2;3 did not. The isoleucine residue at position 254 of HvPIP2;3 was conserved in PIP2 aquaporins of barley, except HvPIP2;4, which possesses methionine instead. CO2 permeability was lost by the substitution of the Ile254 of HvPIP2;3 by methionine, while water permeability was not affected. These results suggest that PIP2 aquaporins are permeable to CO2. and the conserved isoleucine at the end of the E-loop is crucial for CO2 selectivity.

Reconstitution of CO2 Regulation of SLAC1 Anion Channel and Function of CO2-Permeable PIP2;1 Aquaporin as CARBONIC ANHYDRASE4 Interactor

“…These findings also are consistent with our results that pip2;1 T-DNA insertion mutants alone are not sufficient to clearly impair CO 2 -and ABA-induced stomatal closing responses (Figure 7). Nevertheless, given that PIP2 aquaporins are both CO 2 and water permeable (Figures 3E and 5; Supplemental Figure 3) (Shelden et al, 2009;Mori et al, 2014), we hypothesize that PIP2;1 functions in both water transport and CO 2 transport in guard cells. Further research with higher order pip mutants in the many guard cell-expressed plasma membrane aquaporins (Leonhardt et al, 2004;Yang et al, 2008;Zhao et al, 2008;Bauer et al, 2013) will be needed to investigate this hypothesis.…”

“…(Heckwolf et al, 2011). Four barley PIP2 aquaporins were recently shown to display CO 2 permeability in X. laevis oocytes (Mori et al, 2014). Expression of At-PIP2;1 resulted in a change in the surface pH of oocytes (Musa-Aziz et al, 2009, showing that Arabidopsis PIP2;1 is permeable to CO 2 .…”

“…The aquaporins Nt-AQP1 from tobacco, PIP1;2 from Arabidopsis, and four PIP2 proteins in barley (Hordeum vulgare) have been identified as CO 2 transporters in plant cells (Uehlein et al, 2003(Uehlein et al, , 2008(Uehlein et al, , 2012Mori et al, 2014). We investigated whether PIP2;1 can also mediate CO 2 transport.…”

“…We also investigated whether PIP2;1 is involved in the ABA-induced stomatal closing pathway, since the same aquaporins are known to transport water and CO 2 (Figures 3E and 5) (Mori et al, 2014). Genotype-blind stomatal movement imaging analyses of individually mapped stomata showed that pip2;1 single mutant stomata retained intact responses to 10 mΜ ABA treatment in time-course analyses of ABA-induced stomatal closing ( Figure 7C).…”

Genome-wide identification and characterization of aquaporin gene family in common bean (Phaseolus vulgaris L.)

“…SIn plants,everal researchers hypothesize PIP aquaporins have a central role in roots water absorption in rootsfor plant PIP aquaporins, suggesting thatand this proteins could also actively regulate root and leaf hydraulics (Maurel et al 2008;Li et al 2014). In addition to water transport, different studies have showedn that PIPs aquaporins from N. tabacum, A. thaliana and barley could facilitate the diffusion of CO 2 in mesophyll and could directly affect photosynthesis (Flexas et al 2006;Heckwolf et al 2003;Mori et al 2014). The conservation of important transport residues (i.e., NPA motifs and ar/R residues) in common bean PIPs could suggest a similar role of these proteins in regulating water absorption, plant hydraulics and/or CO 2 diffusion.…”