AN ALLELIC SERIES OF BLUE FLUORESCENT TRP1 MUTANTS OF ARABIDOPSIS-THALIANA

Nine blue fluorescent mutants of the flowering plant Arabidopsis thali ana were isolated by genetic selections and fluorescence screens. Each was shown to contain a recessive allele of trp1, a previously describ ed locus that encodes the tryptophan biosynthetic enzyme phosphoribosy lanthranilate transferase (PAT, called trpD in bacteria). The trp1 mut ants consist of two groups, tryptophan auxotrophs and prototrophs, tha t differ significantly in growth rate, morphology, and fertility. The trp1 alleles cause plants to accumulate varying amounts of blue fluore scent anthranilate compounds, and only the two least severely affected of the prototrophs have any detectable PAT enzyme activity. All four of the trp1 mutations that were sequenced are G to A or C to T transit ions that cause an amino acid change, but in only three of these is th e affected residue phylogenetically conserved. There is an unusually h igh degree of sequence divergence in the single-copy gene encoding PAT from the wild-type Columbia and Landsberg erecta ecotypes of Arabidop sis.