Mutations that reduce sinapoylmalate accumulation in Arabidopsis thaliana define loci with diverse roles in phenylpropanoid metabolism.

The products of phenylpropanoid metabolism in Arabidopsis include the three fluorescent sinapate esters sinapoylglucose, sinapoylmalate, and sinapoylcholine. The sinapoylmalate that accumulates in cotyledons and leaves causes these organs to appear blue-green under ultraviolet (UV) illumination. To find novel genes acting in phenylpropanoid metabolism, Arabidopsis seedlings were screened under UV for altered fluorescence phenotypes caused by changes in sinapoylmalate content. This screen identified recessive mutations at four Reduced Epidermal Fluorescence (REF) loci that reduced leaf sinapoylmalate content. Further analyses showed that the ref mutations affected other aspects of phenylpropanoid metabolism and some led to perturbations in normal plant development. A second class of mutations at the Bright Trichomes 1 (BRT1) locus leads to modest reductions in sinapate ester content; however, the most notable phenotype of brt1 mutants is the development of hyperfluorescent trichomes that appear to contain elevated levels of sinapate esters when compared to the wild type. These results indicate that at least five new loci affecting the developmentally regulated accumulation of phenylpropanoid secondary metabolites in Arabidopsis, and the cell specificity of their distribution, have been identified by screening for altered UV fluorescence phenotypes.