Abstract
Uptake and translocation of metal nutrients are essential processes for plant growth. Graminaceous species release phytosiderophores that bind to Fe(3+); these complexes are then transported across the plasma membrane. We have characterized OsYSL15, one of the rice (Oryza sativa) YS1-like (YSL) genes that are strongly induced by iron (Fe) deficiency. The OsYSL15 promoter fusion to beta-glucuronidase showed that it was expressed in all root tissues when Fe was limited. In low-Fe leaves, the promoter became active in all tissues except epidermal cells. This activity was also detected in flowers and seeds. The OsYSL15:green fluorescent protein fusion was localized to the plasma membrane. OsYSL15 functionally complemented yeast strains defective in Fe uptake on media containing Fe(3+)-deoxymugineic acid and Fe(2+)-nicotianamine. Two insertional osysl15 mutants exhibited chlorotic phenotypes under Fe deficiency and had reduced Fe concentrations in their shoots, roots, and seeds. Nitric oxide treatment reversed this chlorosis under Fe-limiting conditions. Overexpression of OsYSL15 increased the Fe concentration in leaves and seeds from transgenic plants. Altogether, these results demonstrate roles for OsYSL15 in Fe uptake and distribution in rice plants.
Highlights
Elsbeth Walker, University of Massachusetts - Amherst S
The expression of OsYSL2, which was induced by Fe deficiency in root and shoots, was similar to that described in a previous report (Koike et al, 2004)
We report the functional roles of OsYSL15 for Fe homeostasis in rice. This was manifested by reduced Fe levels in knockout plants that showed chlorotic phenotypes under Fe deficiency and by increased Fe levels in overexpressors
Summary
Elsbeth Walker, University of Massachusetts - Amherst S. Two insertional osysl mutants exhibited chlorotic phenotypes under Fe deficiency and had reduced Fe concentrations in their shoots, roots, and seeds. Overexpression of OsYSL15 increased the Fe concentration in leaves and seeds from transgenic plants. The plasmalemma root ferric-chelate reductase, FRO2, reduces soil Fe3+ (Robinson et al, 1999) and provides Fe2+ for IRT1, a major metal transporter that takes up Fe2+ into the root epidermis. This is evidenced by the lethal chlorotic phenotypes of IRT1 knockout mutants (Eide et al, 1996; Henriques et al, 2002; Varotto et al, 2002; Vert et al, 2002). Nicotianamine synthase (NAS) catalyzes the trimerization of S-adenosylmethionine molecules to form nicotianamine (NA; Higuchi et al, 1999), which is
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