SUR2 MUTATIONS OF ARABIDOPSIS-THALIANA DEFINE A NEW LOCUS INVOLVED INTHE CONTROL OF AUXIN HOMEOSTASIS

A new auxin homeostasis gene in Arabidopsis called SUR2 has been ident ified. This gene, mapped to the bottom of chromosome 4, is defined by two recessive nuclear mutants designated superroot2 (sur2), which disp lay several abnormalities reminiscent of auxin effects. A number of th ese characteristics are similar to the phenotype of the previously des cribed auxin-overproducing mutant superroot1 (sur1); however, several lines of evidences reveal that the SUR2 gene defines a new key point i n the regulation of endogenous auxin concentrations. The phenotype of the sur1 sur2 double mutant is additive. Analysis by gas chromatograph y coupled to mass spectrometry indicated increased levels of free indo le-3-acetic acid correlated with a decreased level of bound auxin in t he sur2 mutant. These results suggest that SUR2 may be involved in the control of auxin conjugation.