Mitteilungen der Gesellschaft für Pflanzenbauwissenschaften Band 23

Mitt. Ges. Pflanzenbauwiss. 23: 150 (2011)
Three Novel Transporters: Guiding Manganese to the destined place
Bastian Meier, Xi Chen, Annina Gwinner, Tina Peiter-Volk and Edgar Peiter
The Plant Nutrition Laboratory, IAEW, Martin-Luther-University Halle-Wittenberg. E-Mail:
Bastian.Meier@landw.uni-halle.de
Introduction
At least 35 enzymes of a plant cell require Mn as a catalytic site or cofactor,
examples being the water-splitting system of photosystem II and the MnSOD. Even
though Mn is involved in such important processes, the amount required is relatively
low. Acidic soils show elevated levels of plant-available Mn and plants can encounter
Mn toxicity. Plants therefore need to regulate (sub-)cellular Mn homeostasis.
ShMTP8 from Stylosanthes hamata, a highly Mn-tolerant plant, encodes for a Mn
transporter which translocates Mn into the vacuole (Delhaize, 2003). This transporter
is a member of the Cation Diffusion Facilitator (CDF) protein family. The Arabidopsis
genome contains four genes (AtMTP8-AtMTP11) closely related to ShMTP8. Based
on their phylogenetic relationship, these genes may also encode for Mn transporters.
We have previously identified a vesicle trafficking-based mechanism of Mn secretion
in plants, which depends on the operation of AtMTP11 (Peiter, 2007). Here, we
present the other Arabidopsis CDF members with a possible role in Mn homeostasis.
Material und Methods
To analyse the Mn transport activity of the MTPs in Mn-sensitive yeast cells the
respective Saccharomyces cerevisiae strains were dropped onto selective plates
supplemented with Mn. To analyze the role of MTPs in planta T-DNA knockout
mutants were grown on medium with excess manganese. Promotor activity analysis
was done by promoter-GUS fusion. For subcellular localization Arabidopsis mesophyll
protoplasts were transformed with EYFP fusion proteins. EYFP fluorescence
was analyzed by confocal laser scanning microscopy.
Results and Discussion
The heterologous expression of the MTPs in a Mn-sensitive yeast mutant resulted in
an enhanced export of Mn and therefore restored growth of the cells on high-Mn
media, which is in agreement with their function as Mn transporters. Seedlings of
knockout mutants displayed altered growth characteristics compared to the wild type
in conditions of excess Mn and had an altered elemental composition. Interestingly,
some mutants showed an improved tolerance to Mn toxicity. The analysis of promoter
activity shows that the promoter of AtMTP8 is active in flowers. The highest
activity of the AtMTP9 promoter was found in senescent leaves, suggesting an
association with the sequestration of Mn from degrading photosystems. AtMTP10
expression was visualized in the vascular system. The MTP-EYFP fusions showed
that the three proteins operate in different cellular compartments like the vacuole, ER
and vesicles. These results indicate specific roles of the investigated MTP genes in
Mn homeostasis.
References
Delhaize, E. et al. 2003: Genes encoding proteins of the cation diffusion facilitator family that confer
manganese tolerance. Plant Cell 15:1131-1142.
Peiter, E. et al. 2007: A secretory pathway-localized cation diffusion facilitator confers plant manganese
tolerance. Proc. Natl. Acad. Sci. USA 104:8532-8537.