Heavy metal tolerance in the fission yeast requires an ATP-binding cassette-type vacuolar membrane transporter.

Abstract

In response to heavy metal stress, plants and certain fungi, such as the fission yeast Schizosaccharomyces pombe, synthesize small metal‐binding peptides known as phytochelatins. We have identified a cadmium sensitive S. pombe mutant deficient in the accumulation of a sulfide‐containing phytochelatin‐cadmium complex, and have isolated the gene, designated hmt1, that complements this mutant. The deduced protein sequence of the hmt1 gene product shares sequence identity with the family of ABC (ATP‐binding cassette)‐type transport proteins which includes the mammalian P‐glycoproteins and CFTR, suggesting that the encoded product is an integral membrane protein. Analysis of fractionated fission yeast cell components indicates that the HMT1 polypeptide is associated with the vacuolar membrane. Additionally, fission yeast strains harboring an hmt1‐expressing multicopy plasmid exhibit enhanced metal tolerance along with a higher intracellular level of cadmium, implying a relationship between HMT1 mediated transport and compartmentalization of heavy metals. This suggests that tissue‐specific overproduction of a functional hmt1 product in transgenic plants might be a means to alter the tissue localization of these elements, such as for sequestering heavy metals away from consumable parts of crop plants.

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

“…AtMRPs belong to a family of membrane-associated glutathione-conjugate transporters, which forms part of a superfamily called ABC transporters. In the yeast, ABC transporters are involved in the vacuolar sequestration of Cd (Ortiz et al 1992;Wemmie et al 1994). Bovet et al (2003) studied the expression of several AtMRP genes in Cd-exposed A. thaliana.…”

Interactions of fungi with toxic metals

“…Physiological roles in response to such alteration of membrane structure may include detoxification of superoxide or hydroxyl radicals, and/or in zinc homeostasis which may be part of the stress response . Using a cadmium-sensitive mutant of 5. pombe, deficient in the synthesis of a yglutamyl peptide, Ortiz et al (1992) have isolated the gene, hmtl which complements this mutant. The deduced protein sequence of the hmtl gene shares identity with the family of ABC (ATP-binding cassette)-type transport proteins which are integral membrane proteins.…”

“…The deduced protein sequence of the hmtl gene shares identity with the family of ABC (ATP-binding cassette)-type transport proteins which are integral membrane proteins. Analysis of fractionated cell components indicated that the HMTl polypeptide was associated with the vacuolar membrane and it has been proposed that the vacuole plays a central role in y-glutamyl peptide-mediated metal detoxification in S. pombe with S'" being incorporated into the Cd-y-glutamyl peptide in the vacuole (Ortiz et al, 1992). {b) Vacuolar compartmentation.…”

Comparison of Metallothionein Gene Expression and Nonprotein Thiols in Ten Arabidopsis Ecotypes (Correlation with Copper Tolerance)

“…In both fungi and plants, cadmium-PC complexes accumulate in the vacuole (Vogeli-Lange and Wagner, 1990;Speiser et al, 1992); in the fission yeast Sckizosacckaromyces pombe transport of cadmium-PC complexes across the tonoplast occurs via a nove1 multiple drug resistancetype pump (Ortiz et al, 1992(Ortiz et al, , 1995Ow, 1993). PCs are synthesized nontranslationally from glutathione by the enzyme PC synthase, which is strongly activated by metal ions (Gupta and Goldsbrough, 1991).…”