Several metal transporters in plants accommodate multiple cations, including
some which are toxic to humans. Attempts at increasing iron and zinc content
of rice endosperm by overexpressing metal transporters unintentionally led
to accumulation of copper, manganese, and cadmium. Unlike other metal
transporters, the barley Yellow Stripe 1 (HvYS1) is specific for iron.

The team of Raviraj Banakar of the Universitat de Lleida-Agrotecnio Center
Lleida investigated the basis of this preference by expressing HvYS1 in rice
under the control of the maize ubiquitin1 promoter. Plants expressing HvYS1
had slight increases in iron uptake, translocation, seed accumulation, and
endosperm loading, but had no changes in the uptake of zinc, manganese or
copper. The zinc and manganese levels in the endosperm did not differ
between the wild-type and HvYS1 lines, but the latter had significantly
lower copper levels. The transgenic lines also showed a significantly
reduced cadmium uptake, translocation, and accumulation in the rice seeds.

These results suggest that HvYS1 promotes the preferential mobilization and
loading of iron. The increased loading of iron displaces copper and cadmium
in the rice seeds.

[onlinelibrary.wiley.com]



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