Suppressors of trpl Fluorescence ldentify a New Arabidopsis Gene , TRP 4 , Encoding the Anthranilate Synthase Subunit

Suppressors of the blue fluorescence phenotype of the Arabidopsis trp7-700 mutant can be used to identify mutations in genes involved in plant tryptophan biosynthesis. Two recessive suppressor mutations define a new gene, TRP4. The trp4 mutant and the trp7-700 mutant are morphologically normal and grow without tryptophan, whereas the trp4; trp7700 double mutant requires tryptophan for growth. The trp4; trp7-700 double mutant does not segregate at expected frequencies in genetic crosses because of a female-specific defect in transmission of the double mutant genotype, suggesting a role for the tryptophan pathway in female gametophyte development. Genetic and biochemical evidence shows that trp4 mutants are defective in a gene encoding the fi subunit of anthranilate synthase (AS). Arabidopsis AS fi subunit genes were isolated by complementation of an Escherichia col i anthranilate synthase mutation. The trp4 mutation cosegregates with one of the genes, ASB7, located on chromosome 1. Sequence analysis of the AS67 gene from trp4-7 and trp4-2 plants revealed different single base pair substitutions relative to the wild type. Anthranilate synthase a and p subunit genes are regulated coordinately in response to bacterial pathogen infiltration.