Abstract:
Manganese (Mn2?) is an essential micronutrient
in plants. However increased Mn2? levels are
toxic to plant cells. Metal tolerance proteins (MTPs),
member of cation diffusion facilitator protein (CDF)
family, have important roles in metal homeostatis in
different plant species and catalyse efflux of excess
metal ions. In this study, we identified and characterized
two MTP genes from Beta vulgaris spp. maritima
(B. v. ssp. maritima). Overexpression of these two
genes provided Mn tolerance in yeast cells. Sequence
analyses displayed BmMTP10 and BmMTP11as
members of the Mn-CDF family. Functional analyses
of these proteins indicated that they are specific to
Mn2? with a role in reducing excess cellular Mn2?
levels when expressed in yeast. GFP-fusion constructs
of both proteins localized to the Golgi apparatus
as a punctuated pattern. Finally, Q-RT-PCR results
showed that BmMTP10 expression was induced
threefold in response to the excess Mn2? treatment.
On the other hand BmMTP11 expression was not
affected in response to excess Mn2? levels. Thus, our
results suggest that the BmMTP10 and BmMTP11
proteins from B. v. ssp. maritima have non-redundant
functions in terms of Mn2? detoxification with a
similar in planta localization and function as the
Arabidopsis Mn-CDF homolog AtMTP11 and this
conservation shows the evolutionary importance of
these vesicular proteins in heavy metal homeostatis
among plant species.
