Functional characterization of the root anion channels SLAH1 and SLAH4: involvement in Cl- and NO3- nutrition and interaction with abiotic stress

Abstract

We aim to characterize genes and plasma membrane (PM) transporters involved in the uptake and long-distance transport of chloride (Cl-; Colmenero-Flores et al, 2007; Brumós et al, 2009; Brumós et al, 2010). Under most circumstances, at PM potentials more negative than -50 mV, chloride channels mediate passive Cl- efflux. In peripherall root cell layers, Cl- channles have been proposed to make a considerable contribution to net Cl- uptake, which results from combined activities of influx (active) and efflux transport mechanisms. In the root vasculature, different Cl- conductance activities measured in xylem parenchyma cells participate in root-to-shoot translocation of Cl- and nitrate (NO3-). PM anion channels can be broadly classified on the basis of their voltage dependence into depolarization- and hyperpolarization-activated channels. Depolarization-activated anion channels can be subdivided further based on their kinetics and gating properties into R(rapid)-type, S(slow)-type, and outwardly rectifying anion channels. The physiological role of R- and S-type channels was elucidated in guard cells using electrophysiological analyses, where R- and S-type channels were respectively named QUAC, for QUick Anion Channel, and SLAC, for SLow Anion Channel. These channels, activated by the drought hormone abscisic acid (ABA), are involved in the early steps leading to stomata closure (Geiger et al, 2009; Dreyer et al, 2012). The molecular nature of the guard cell slow anion channel has been uncovered and the gene encoding for this transporter was named SLAC1 (Negi et al., 2008). SLAH3 (SLAC1 Homolog 3) represents a second S-type channel present in guard cells which exhibits a higher preference for NO3- (Geiger et al., 2011). Other members of the SLAC family, SLAH1 and SLAH4 (SLAC1 Homolog 1 and 4) may encode for root isoforms of the S-type channels (Brumos et al, 2010). Under this hypothesis, we have initiated the molecular characterization of AtSLAH1 and AtSLAH4 genes. Data concerning gene expression, abiotic stress response and knock-out phenotypes will be presented.