Characterization of the first higher plant histidine auxotroph: a tool for herbicide development and phytoremediation studies

The Arabidopsis root meristemledd2 mutants were originally charcterized as dwarfs that develop an extremely short primary roots showing limited cell proliferation at the tip. We have demonstrated that treatment with L-histidine allows these mutants to gro w as wildtype plants suggesting that they are the first histidine auxotrophs identified at the whole-plant level. Imidazoleglycerolphosphate dehydratase (IGPD) is the only histidine-biosynthetic gene located in the recently-sequenced region of Arabidopsis chromosome 3 where RML2 was previously mapped indicating that they most probably represent the same locus. We wish to test this hypothesis by complementing the rml2 mutants with an AtIGPD-producing construct and by cloning and sequencing the IGPD mutant s alleles. Further characterization of the mutants through histidine determination and measuring the activity of the lmutant enzymes will render them extremely useful as tools for studies involving herbicide development, phytoremediation and metabolic path way gene regulation.