|
Summary of Research Projects (Supports in 2005
Fiscal Year)
| Subjects |
Mechanism of Biosynthesis, Distribution, and Transport
of Hemes in Higher Plants |
Representative
researcher |
The University of Tokyo Tatsuru MASUDA |
| In plant cells, heme is synthesized in
plastids and transported to various organelles. Our previous study showed
that oxidative stresses induced the expression of isoforms of plastidic
heme biosynthetic enzymes (HEMA2 and FC1), together with various defensive
hemoproteins outside plastids, indicating heme distribution is important
for defensive function in plant cells. Since the mechanism by which the
proteins in organelles receive their hemes from plastids is poorly understood,
here we examined the mechanism of biosynthesis, distribution, and transport
of hemes in Arabidopsis thaliana. To determine a small amount
of heme, we first developed extremely sensitive heme assay using chemiluminescent
detection. With this method, we showed the oxidative stress increased heme
levels in wild-type Arabidopsis, whereas such increase was repressed
in knock-out Arabidopsis mutants of HEMA2 and FC1. These results
are first demonstration of the existence of the heme biosynthetic pathway
responsive to oxidative stresses in plastids, which may function heme supply
for defensive hemoproteins. To elucidate heme transport in cytosols, we
then analyzed putative cytosolic heme binding proteins (HBP), homologous
to animal p22HBP/SOUL family. Purified recombinant HBPs showed specific
binding to heme, while they non-specifically bound to other metal porphyrins.
Biochemical and physiological analysis of Arabidopsis HBPs are
currently underway. |
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