The rare alkali ion caesium (Cs+) is assimilated by eukaryotes, even though it is not an
essential nutrient. It poses an environmental concern through the anthropogenic release of
its radioisotopes, 134Cs and 137Cs. Bioavailability and long half-lives favour its uptake and
accumulation in plants, via which radiocaesium can be introduced to the food chain. Cs+ ions
are taken up via potassium-(K+)-related pathways due to the biophysical similarity of these
cations. This makes it difficult to solely manipulate Cs+ accumulation in plants without
disturbing the homeostasis of essential ions at the same time.
This work shows that the soluble N-ethylmaleimide sensitive factor attachment receptor
(SNARE) Sec22p, previously described as a member of the protein sorting machinery,
specifically affects Cs+ accumulation in yeast by regulating the selectivity of vacuolar
deposition. A similar phenotype became apparent for a homologous plant protein, SEC22.
The loss of Saccharomyces cerevisiae Sec22p reduces Cs+ uptake by more than half, while
at the same time leaving essential cations undisturbed. Mathematical modelling of wild-type
and mutant Cs+ uptake kinetics proposes that sec22Δ is defective in vacuolar
compartmentalisation of Cs+, which is proven by biochemical fractionation. Morphological
alterations were not produced by the loss of Sec22p, only a Cs+-dependent vacuolar
fragmentation can be observed. These results indicate a so far undescribed function of
Sec22p in assuring a non-selective ion deposition to the vacuole, which is necessary in ion
detoxification, while its loss induces discrimination against vacuolar Cs+ deposition. A
developmentally controlled loss-of-function mutant of the orthologous gene SEC22
(At1g11890) in A. thaliana displays a similar phenotype, having specifically reduced Cs+
enrichment without detrimental growth defects, thereby translating the yeast findings to a
multicellular context. Furthermore, a functional complementation of the yeast mutant Cs+
phenotype by the plant gene transcript was possible. Selective reduction of Cs+ accumulation
in plants by loss of a single gene product represents a new route to limit radiocaesium input
to the food chain without disturbing basic plant nutrition and growth.
| Identifer | oai:union.ndltd.org:MUENCHEN/oai:edoc.ub.uni-muenchen.de:15650 |
| Date | 14 December 2012 |
| Creators | Dräxl, Stephan Johann |
| Publisher | Ludwig-Maximilians-Universität München |
| Source Sets | Digitale Hochschulschriften der LMU |
| Detected Language | English |
| Type | Dissertation, NonPeerReviewed |
| Format | application/pdf |
| Relation | http://edoc.ub.uni-muenchen.de/15650/ |
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