An update on the ABCC transporter family in plants: many genes, many proteins, but how many functions?

Abstract

The ABCC subfamily of the ATP binding cassette (ABC) transporters, which were formerly known as multidrug resistance-related proteins (MRPs), consists of closely related members found in all eukaryotic organisms. Although more than a decade of intensive research has elapsed since the first MRP protein was functionally characterised in Arabidopsis thaliana, knowledge of this particular transporter family is still limited in plants. Although ABCC proteins were originally defined as vacuolar pumps of glutathione-S (GS) conjugates, evidence, as well as speculation, on their endogenous functions inside the cell ranges from detoxification and heavy metal sequestration, to chlorophyll catabolite transport and ion channel regulation. The characterisation of knockout mutants in Arabidopsis has been pivotal for elucidation of different roles of ABCC transporters. However, a functional annotation for the majority of these transport proteins is still lacking, even in this model plant. On the one hand, this problem seems to be caused by functional redundancy between family members, which might lead to physiological complementation by a highly homologous gene in the mutant lines. On the other hand, there is growing evidence that the functional diversity of ABCC genes in Arabidopsis and other plants is far greater than previously assumed. For example, analysis of microarray expression data supports involvement of ABCC transporters in the response to biotic stress: particular changes in ABCC transcript levels are found, which are pathogen-specific and evoke distinct signalling cascades. Current knowledge about plant ABCC transporters indicates that novel and unexpected functions and substrates of these proteins are still waiting to be elucidated.

Regulating the Redox Gatekeeper: Vacuolar Sequestration Puts Glutathione Disulfide in Its Place

“…Based on current concepts, the best candidates to perform this transfer are members of the multidrug resistance-associated protein (MRP) family, now denoted subclass C of the ATP-binding cassette (ABC) translocators (Klein et al, 2006;Rea, 2007). In Arabidopsis, 15 ABCC genes (for subclass C of the ABC transporters) have been described (ABCC1-ABCC15; Wanke and Kolukisaoglu, 2010).…”

“…The corresponding proteins are probably localized at the tonoplast, although some may also be found at the plasmalemma (Wanke and Kolukisaoglu, 2010). Of them, ABCC1 and ABCC2 are the best studied.…”

“…paralogous ABCC genes is coregulated to some extent (Wanke and Kolukisaoglu, 2010), and this may contribute to the coordinated up-regulation of multiple genes by oxidative stress.…”

The Blood-Testis Barrier and Its Implications for Male Contraception

“…Multidrug resistance-related proteins. MRP is another efflux transporter subfamily of the ABC transporter, consisting of MRP1 (ABCC1), MRP2 (ABCC2), and MRP3 (ABCC3), found in mammalian cells, as well as in plants and bacteria (Rappa et al, 1999;Pérez-Tomá s, 2006;Paumi et al, 2009;Gu and Manautou, 2010;Wanke and Kolukisaoglu, 2010). MRP1 was found to be expressed at relatively high levels in the mouse testis versus other organs.…”

Arsenic tolerance in plants: “Pas de deux” between phytochelatin synthesis and ABCC vacuolar transporters

“…PC synthesis and their complexation to As(III) are coordinated to the transport of the PC-As(III) complex to the vacuole subcellular compartment through the activity of two members of a subclass of ATP binding cassette (ABC) transporters: ABCC1 and -2. Two ATP Binding Cassette Transporters for Shuttling As(III)-PC 2 into Plant Vacuoles ATP binding cassette (ABC) C transporters (15,16) are a subclass of ABC transporters, two of them being known to detoxify As in humans by transporting GSH-As complexes (17). The 15 members of the Arabidopsis ABCC family, many of which are localized at the tonoplast and some of which transport GSH conjugates, were, therefore, good candidates to be scrutinized for As detoxification.…”