Abstract
The Arabidopsis thaliana AtOPT3 belongs to the oligopeptide transporter (OPT) family, a relatively poorly characterized family of peptide/modified peptide transporters found in archebacteria, bacteria, fungi, and plants. A null mutation in AtOPT3 resulted in embryo lethality, indicating an essential role for AtOPT3 in embryo development. In this article, we report on the isolation and phenotypic characterization of a second AtOPT3 mutant line, opt3-2, harboring a T-DNA insertion in the 5' untranslated region of AtOPT3. The T-DNA insertion in the AtOPT3 promoter resulted in reduced but sufficient AtOPT3 expression to allow embryo formation in opt3-2 homozygous seeds. Phenotypic analyses of opt3-2 plants revealed three interesting loss-of-function phenotypes associated with iron metabolism. First, reduced AtOPT3 expression in opt3-2 plants resulted in the constitutive expression of root iron deficiency responses regardless of exogenous iron supply. Second, deregulation of root iron uptake processes in opt3-2 roots resulted in the accumulation of very high levels of iron in opt3-2 tissues. Hyperaccumulation of iron in opt3-2 resulted in the formation of brown necrotic areas in opt3-2 leaves and was more pronounced during the seed-filling stage. Third, reduced AtOPT3 expression resulted in decreased accumulation of iron in opt3-2 seeds. The reduced accumulation of iron in opt3-2 seeds is especially noteworthy considering the excessively high levels of accumulated iron in other opt3-2 tissues. AtOPT3, therefore, plays a critical role in two important aspects of iron metabolism, namely, maintenance of whole-plant iron homeostasis and iron nutrition of developing seeds.
Highlights
The Arabidopsis thaliana AtOPT3 belongs to the oligopeptide transporter (OPT) family, a relatively poorly characterized family of peptide/modified peptide transporters found in archebacteria, bacteria, fungi, and plants
ZmYS1 belongs to the oligopeptide transporter (OPT) family, a relatively poorly characterized family of transporter proteins involved in the transport of peptides and amino acid-derived compounds
We recently showed by two-electrode voltage-clamp studies in Xenopus oocytes that the Saccharomyces cerevisiae ScOPT1p and the Arabidopsis AtOPT4 are protoncoupled transporters with broad but distinct substrate specificities and affinities (Osawa et al, 2006)
Summary
The Arabidopsis thaliana AtOPT3 belongs to the oligopeptide transporter (OPT) family, a relatively poorly characterized family of peptide/modified peptide transporters found in archebacteria, bacteria, fungi, and plants. Reduced AtOPT3 expression in opt plants resulted in the constitutive expression of root iron deficiency responses regardless of exogenous iron supply. Reduced AtOPT3 expression resulted in decreased accumulation of iron in opt seeds. The double mutant exhibited interveinal chlorosis and reduced fertility due to defective anther and embryo development These results indicate that YSL proteins are important in the transport of chelated Fe, most likely Fe(II)-NA, especially to developing seeds. We recently showed by two-electrode voltage-clamp studies in Xenopus oocytes that the Saccharomyces cerevisiae ScOPT1p and the Arabidopsis AtOPT4 are protoncoupled transporters with broad but distinct substrate specificities and affinities (Osawa et al, 2006)
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