75 Integrating Membrane Transport with Male Gametophyte ... - TAIR

333 Regulation of Fructose-1,6-Bisphosphate Aldolase via Glutathionylation in Arabidopsis
Chloroplasts
Matsumoto Masayoshi, Ogawa Ken'ich
RIBS Okayama
The role of glutathionylation of fructose-1, 6-bisphosphate aldolase (FBA) in chloroplasts was investigated. The
Arabidopsis genome includes three genes for chloroplastic FBAs, of which glutathionylated FBA was designated as
FBA1. Recombinant FBA1 activity had a strongly pH-dependency, which suited stromal pH that changes from 7 to 8
following illumination: FBA1 activity at pH 8 was 2-fold higher than at pH 7. Glutathione (GSH) strengthened this pHdependency
by 250 %. Other FBAs did not have such features.
Thioredoxin (Trx) activates the Calvin cycle, but dithiothreitol and Trx inhibited the activity of three FBAs. At pH
8, GSH reactivated FBA1 only via glutathinonylation. FBA activity in wild-type chloroplasts was regulated by GSH and
pH as was FBA1, while that in a T-DNA inserted mutant of FBA1 was little affected by GSH or pH. Altogether, FBA1
is expressed in vivo and regulated via glutathionylation to activate and facilitate the Calvin cycle.
334 The FRO3 Fe(III) Chelate Reductase Plays A Vital Role In Iron Homeostasis In Arabidopsis
Indrani Mukherjee, Erin Connolly
University of South Carolina, Department of Biological Sciences, Columbia, SC 29208
The Arabidopsis FRO2 gene encodes the iron-deficiency inducible Fe(III) chelate reductase responsible for reduction
of iron at the root surface; subsequent transport of iron across the plasma membrane is carried out by a ferrous iron
transporter (IRT1). Seven additional FRO genes are present in the Arabidopsis genome and our current studies are
aimed at determining the functions of each FRO family member. After iron is taken up by root cells, it is thought that
iron is re-oxidized to the ferric form and is transported as Fe(III)-citrate via the xylem to the aerial parts of the plant.
Fe(III) chelate reductase activity is required for further iron uptake by leaf cells; FROs may also function in reduction
of iron at various organellar membranes. We used real time RT-PCR to examine the expression of each FRO gene in
different tissues and in response to iron limitation. FRO3 is expressed at high levels in leaves and roots of seedlings
and expression of FRO3 is induced by iron-deficiency. FRO3-GUS transgenic plants reveal that the FRO3 promoter is
primarily active in the vascular tissue of the plant and FRO3-GFP stable transgenic lines show that FRO3 is localized at
the plasma membrane. Analysis of a FRO3-KO line shows that iron accumulation is altered in this line as compared to
wild type as is the expression of a variety of genes involved in iron uptake, localization and storage. Taken together, our
results show that FRO3 functions in maintenance of iron homeostasis and suggest that FRO3 functions in long-distance
transport of iron.