MAP-BASED CLONING OF CHLORONERVA - A GENE INVOLVED IN IRON UPTAKE OF HIGHER PLANTS ENCODING NICOTIANAMINE SYNTHASE

¹ Present address: Institut fuer Pflanzenbiologie, Universitaet Zuerich, Zollikerstr. 107, CH-8008 Zuerich, Switzerland

² Institute for Plant Genetics and Crop Plant Research, Corrensstr. 3, D-06466 Gatersleben, Germany

The uptake of iron in plants is a highly regulated process. In tomato, the mutant chloronerva is deregulated in its iron uptake mechanisms exhibiting constitutive expression of iron uptake responses and intercostal chlorosis. Biochemically, chloronerva is an auxotroph for nicotianamine - a key polyamine in plant iron uptake metabolism. The chloronerva gene has been fine-mapped onto the long arm of chromosome 1 in a large segregating tomato population and YAC clones encompassing the region were isolated using flanking markers. A cosmid contig containing the chloronerva gene was established and complementing cosmids were identified by transformation into the mutant. The chloronerva transcript was identified by cDNA isolation with the complementing cosmids. The gene encodes a novel protein of 35 kD. It harbors a single base pair change in the mutant compared to the wildtype. Based on sequence similarity to the purified barley enzyme and its coding DNA sequence the chloronerva gene encodes the enzyme nicotianamine synthase.