Plant Molecular Biology 54: 125–136, 2004.
© 2004 Kluwer Academic Publishers. Printed in the Netherlands.
Isolation and characterization of Fe(III)-chelate reductase gene LeFRO1
Lihua Li, Xudong Cheng and Hong-Qing Ling
State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental
Biology, Chinese Academy of Sciences, Datun Road, Andingmenwai, Beijing 100101, China (
correspondence; e-mail firstname.lastname@example.org)
Received 2 October 2003; accepted in revised form 13 January 2004
Key words: chloronerva, Fe(III)-chelate reductase, iron uptake, LeFRO1, T3238fer,tomato
Tomato is a model plant for studying molecular mechanisms of iron uptake and metabolism in strategy I plants
(dicots and non-graminaceous monocots). Reduction of ferric to ferrous iron on the root surface is an obligat-
ory process for iron acquisition from soil in these plants. LeFRO1 encoding an Fe(III)-chelate reductase protein
was isolated from the tomato genome. We show that expression of LeFRO1 in yeast increases Fe(III)-chelate
reductase activity. In a transient expression analysis we found that LeFRO1 protein was targeted on the plasma
membrane. LeFRO1 transcript was detected in roots, leaves, cotyledons, ﬂowers and young fruits by RT-PCR
analysis. Abundance of LeFRO1 mRNA was much lower in young fruits than in other tissues. The transcription
intensity of LeFRO1 in roots is dependent on the iron status whereas it is constitutively expressed in leaves. These
results indicate that LeFRO1 is required in roots and shoots as well as in reproductive organs for iron homeostasis
and that its transcription in roots and shoots is regulated by different control mechanisms. The expression of
LeFRO1 was disrupted in the iron-inefﬁcient mutants chloronerva and T3238fer, indicating that FER and CHLN
genes are involved in the regulation of LeFRO1 expression in tomato roots. The differential expression of LeFRO1
and LeIRT1 (an iron-regulated metal transporter gene in tomato) in roots of T3238fer under iron-deﬁcient and
-sufﬁcient conditions suggests that the FER gene may regulate expression of LeFRO1 more directly than that of
LeIRT1 in tomato roots.
Iron is an essential nutrient for plants. It functions as
a component of many important enzymes and proteins
involved in fundamentally biochemical processes such
as photosynthesis, respiration and nitrogen reduction.
Deﬁciency in iron results in a strong decrease in levels
of Fe-containing pigment proteins and chlorophylls,
consequently developing chlorosis in young leaves.
Severe iron deﬁciency can lead to a dramatic reduc-
tion in crop yield and even to complete crop failure.
Although abundant in soil, iron is one of the most
common nutrients limiting plant growth in the world
(Guerinot, 2001) because it exists predominantly in
an oxidized ferric form [Fe(III)] in aerobic environ-
ments. The ferric iron has an extremely low solubility
at neutral or basic pH and is not readily available to
plants. To utilize iron elements efﬁciently for growth
and development, two effective iron acquisition sys-
tems known as strategy I and strategy II (Roemheld
and Marschner, 1986) have evolved in higher plants.
All dicots and non-graminaceous monocots use the
strategy I mechanism to acquire iron from soil under
iron deﬁciency stress. The cores of this strategy are
(1) acidiﬁcation of the rhizosphere by enhanced extru-
sion of proton to increase solubility of ferric iron, (2)
activation of ferric-chelate reductase reducing Fe
on the root surface in the subapical region and (3)
induction of the high-afﬁnity Fe
to absorb ferrous iron from soil into roots (Guerinot
and Yi, 1994). Grasses are strategy II plants using the
chelation mechanism to take up iron from soil. Un-