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

Reference ID

54978

Title

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

Source

J Biol Chem, 2009, vol. 284, pp. 8449-8460

Authors (9)

Raichaudhuri-A	Peng-M
Naponelli-V	Chen-S
Sanchez-Fernandez-R	Gu-H
Gregory-J-F-3rd	Hanson-A-D
Rea-P-A

Abstract

The vacuoles of pea (Pisum sativum) leaves and red beet (Beta vulgaris) storage
root are major sites for the intracellular compartmentation of folates. In the
light of these findings and preliminary experiments indicating that some plant
multidrug resistance-associated protein (MRP) subfamily ATP-binding cassette
transporters are able to transport compounds of this type, the Arabidopsis
thaliana vacuolar MRP, AtMRP1 (AtABCC1), and its functional equivalent(s) in
vacuolar membrane vesicles purified from red beet storage root were studied. In
so doing, it has been determined that heterologously expressed AtMRP1 and its
equivalents in red beet vacuolar membranes are not only competent in the
transport of glutathione conjugates but also folate monoglutamates and
antifolates as exemplified by pteroyl-l-glutamic acid and methotrexate (MTX),
respectively. In agreement with the results of these in vitro transport
measurements, analyses of atmrp1 T-DNA insertion mutants of Arabidopsis ecotypes
Wassilewskia and Columbia disclose an MTX-hypersensitive phenotype. atmrp1 knock-
out mutants are more sensitive than wild-type plants to growth retardation by
nanomolar concentrations of MTX, and this is associated with impaired vacuolar
antifolate sequestration. The vacuoles of protoplasts isolated from the leaves
of Wassilewskia atmrp1 mutants accumulate 50% less [(3)H]MTX than the vacuoles
of protoplasts from wild-type plants when incubated in media containing
nanomolar concentrations of this antifolate, and vacuolar membrane-enriched
vesicles purified from the mutant catalyze MgATP-dependent [(3)H]MTX uptake at
only 40% of the capacity of the equivalent membrane fraction from wild-type
plants. AtMRP1 and its counterparts in other plant species therefore have the
potential for participating in the vacuolar accumulation of folates and related
compounds.