Disruption of AtMRP4, a guard cell plasma membrane ABCC‐type ABC transporter, leads to deregulation of stomatal opening and increased drought susceptibility

Abstract

SummaryATP-binding cassette (ABC) transporters are membrane proteins responsible for cellular detoxi®cation processes in plants and animals. Recent evidence shows that this class of transporters may also be involved in many other cellular processes. Because of their homology with human multidrug resistance-associated proteins (MRP), cystic ®brosis transmembrane conductance regulator (CFTR) and sulfonylurea receptor (SUR), some plant ABC transporters have been implicated in the regulation of ion channel activities. This paper describes an investigation of the AtMRP4 gene and its role in stomatal regulation. Reporter gene studies showed that AtMRP4 is highly expressed in stomata and that the protein is localized to the plasma membrane. Stomatal aperture in three independent atmrp4 mutant alleles was larger than in wild-type plants, both in the light and in the dark, resulting in increased water loss but no change in the photosynthetic rate. In baker's yeast, AtMRP4 shows ATP-dependent, vanadate-sensitive transport of methotrexate (MTX), an antifolate and a substrate of mammalian MRPs. Treatment with MTX reduced stomatal opening in wild-type plants, but had no effect in atmrp4 mutants. These results indicate the involvement of AtMRP4 in the complex regulation of stomatal aperture.

Plant Vacuolar ATP-binding Cassette Transporters That Translocate Folates and Antifolates in Vitro and Contribute to Antifolate Tolerance in Vivo

“…Although AtMRP4 (ABCC4) is also able to transport these compounds at high capacity (17), its exact membrane localization is unclear. On the one hand, it localizes to the plasma membrane rather than the vacuolar membrane when its partial translation product is fused with green fluorescent protein (18). On the other hand, the results of recent Arabidopsis organellar proteomic analyses and studies of constructs in which green fluorescent protein is C-terminally fused to the full-length translation product are consistent with localization to the vacuolar membrane (19).…”

A Proteomics Dissection of Arabidopsis thaliana Vacuoles Isolated from Cell Culture

“…These predictions show that the in silico subcellular localization prediction algorithms are probably not robust enough. Surprisingly we also found MRP4 in the tonoplast, whereas Klein et al (68) using confocal microscopy analysis of onion epidermal cells transiently expressing At-MRP4-EGFP showed fluorescence at the periphery of cells, suggesting that AtMRP4 protein was located at the plasma membrane. In support of our data, previous proteomics studies confirm the presence of MRP4 in the purified vacuolar fractions (40,42), but both localizations could be possible.…”

Isolation of Zn-responsive genes from two accessions of the hyperaccumulator plant Thlaspi caerulescens

“…Recent Wndings indicate that MRP transporters have also other roles besides detoxiWcation, and the vacuolar location has been questioned. In Arabidopsis, AtMRP4 has a function in stomatal opening (Klein et al 2004). The possible role of TcMRP10 in metal sequestration thus remains open.…”