Binding of Sulfonylurea by AtMRP5, an Arabidopsis Multidrug Resistance-Related Protein That Functions in Salt Tolerance

Abstract

Recently, a new member of the ABC transporter superfamily of Arabidopsis, AtMRP5, was identified and characterized. In the present work, we found that AtMRP5 can bind specifically to sulfonurea when it is expressed in HEK293 cells. We also present evidence for a new role of AtMRP5 in the salt stress response of Arabidopsis. We used reverse genetics to identify an Arabidopsis mutant (atmrp5-2) in which the AtMRP5 gene was disrupted by transferred DNA insertion. In root-bending assays using Murashige and Skoog medium supplemented with 100 mm NaCl, root growth of atmrp5-2 was substantially inhibited in contrast to the almost normal growth of wild-type seedlings. This hypersensitive response of the atmrp5-2 mutant was not observed during mannitol treatment. The root growth of the wild-type plant grown in Murashige and Skoog medium supplemented with the MRP inhibitor glibenclamide and NaCl was inhibited to a very similar extent as the root growth of atmrp5-2 grown in NaCl alone. The Na ϩ -dependent reduction of root growth of the wild-type plant in the presence of glibenclamide was partially restored by diazoxide, a known K ϩ channel opener that reverses the inhibitory effects of sulfonylureas in animal cells. Moreover, the atmrp5-2 mutant was defective in 86 Rb ϩ uptake. When seedlings were treated with 100 mm NaCl, atmrp5-2 seedlings accumulated less K ϩ and more Na ϩ than those of the wild type. These observations suggest that AtMRP5 is a putative sulfonylurea receptor that is involved in K ϩ homeostasis and, thus, also participates in the NaCl stress response.The ATP-binding cassette (ABC) transporter superfamily is the largest known membrane transporter protein family, and its members are capable of a multitude of transport functions (Higgins, 1992(Higgins, , 1995. These proteins are highly interesting because of their involvement in numerous pathologies, such as cystic fibrosis, diabetes, and multidrug resistance (Demolombe and Escande, 1996). In animals, two ABC proteins are directly involved in regulating ion channels in the plasma membrane, specifically ATPsensitive potassium channels (K ATP channels) and the cystic fibrosis transmembrane conductance regulator (CFTR). K ATP channels were initially identified in the heart (Noma, 1983) and are complexes composed of an inward rectifier K ϩ channel and an ABC protein, the sulfonylurea receptor (Babenko et al., 1998; Miki et al., 1999). K ATP channels are highly specific for K ϩ and are inhibited by micromolar concentrations of intracellular ATP. CFTR is a chloride channel expressed by a variety of secreting epithelial cells that is regulated by cAMP-dependent phosphorylation and ATP (Anderson et al., 1991; Bear et al., 1992). These channels serve to link the electrical activity of cell membranes with cellular metabolism.The presence of ABC proteins in plants was established by the cloning of several genes encoding members of this group in Arabidopsis and other species (Dudler and Hertig, 1992; Smart and Fleming, 1996; Davies et al., 1997; Lu et al., 1997 Lu...

Effect of transporters on the secretion of phytochemicals by the roots of Arabidopsis thaliana

“…Geisler et al (2005) used MDR/PGP inhibitors cyclosporin A and verapamil to inhibit the eZux of auxin in PGP 1 transformed yeast. By studying the hypersensitive response of A. thaliana to salt stress, glibenclamide was used to analyze the response of the atmrp5-2 mutant (Lee et al 2004). As shown in Table 2, the secretion of some of the phytochemicals produced by Arabidopsis was inhibited by these compounds, suggesting that a primary transporter might be involved in their exudation into the medium.…”

A Novel MYBS3-Dependent Pathway Confers Cold Tolerance in Rice

“…In the microarray analysis, among the 17 genes up-regulated by at least 3-fold by overexpression of MYBS3 as well as by cold in the wild type (Supplemental Fig. S4A), several of them have previously been implicated in stress responses and/or tolerance in plants (Supplemental Table S1), such as Glu decarboxylase, which catalyzes the conversion of Glu to g-aminobutyrate and is activated in response to heat in Arabidopsis roots (Bouche et al, 2004) and to anoxia in rice roots (Aurisano et al, 1995); WRKY77, which activates the ABA-inducible HVA22 promoter in cereal grains (Xie et al, 2005), and several WRKYs have been shown to confer biotic and abiotic stress tolerance in Arabidopsis (Ross et al, 2007;Lai et al, 2008;Zhou et al, 2008); and multidrug resistance protein 4, whose expression is activated by arsenate and arsenite stresses in rice seedlings (Chakrabarty et al, 2009) and whose homologous genes confer salt tolerance (Lee et al, 2004) and oxidative stress tolerance against pathogens (Sun et al, 2006) in various plant species.…”

ATP-Sensitive Cation-channel in Wheat (<i>Triticum durum</i> Desf.): Identification and Characterization of a Plant Mitochondrial Channel by Patch-clamp

“…Interestingly, SUR1 (AAC36724) and SUR2A (NP_005682.2) subunits both show a high degree of sequence homology with several members of the multidrug-resistance protein family in Arabidopsis, including the ABC transporters of mitochondrion (AtATM1-3) (32% identity and 53% positivity over 1381 aminoacids (BLASTP algorithm) between SUR1 and AtMRP1). While AtATM1-3 proteins are implicated in iron homeostasis [31], AtMRP5 has been proposed to regulate a potassium channel activity [32]. Thus, one possibility is that an ABC-transporter protein associates with e.g.…”