Characterization of semi-dominant alleles of REF4 and their impact on phenylpropanoid accumulation in Arabidopsis
Throughout time, plants have evolved the capacity to biosynthesize an array of "secondary metabolites" that play diverse roles in plant growth, development, metabolism, and signaling both within plants and between plants and other organ- isms. One subset of secondary metabolites are the phenylpropanoids, a structurally- diverse class of compounds that include avonoids, coumarins, monolignols (and the heteropolymer made from them, lignin), suberin, sporopollenin, and the hydroxycin- namic acid esters. The UV-fluorescent nature of sinapoylmalate has served as a genetic marker to screen for mutants that are deficient in various enzymatic steps of phenylpropanoid metabolism. The research presented in this thesis explores the phenotypes of reduced epidermal uorescence 4. The ref4 mutant alleles generated by ethylmethane sulfonate mutagenesis are semi-dominant and exhibit a range of pleiotropic phenotypes, including a reduction in the accumulation of avonoids, lignin, and hydroxycinnamic esters. This observation suggests that the perturbation in phenylpropanoid metabolism occurs early in the pathway. REF4 was cloned and found to encode a large protein of unknown function that is predicted to be plasma membrane localized. The semi-dominance of the mutant alleles was confirmed by a.) reducing the REF4-3 transcript levels in the mutant by RNAi, b.) introducing the REF4-3 allele into the wild type, and c.) identifying an intragenic suppressor mutant. Finally, experiments testing the function of the phenylpropanoid pathway in ref4 suggest that 4-coumarate CoA ligase activity is reduced, which may be the cause of the phenylpropanoid-related mutant phenotypes.
Chapple, Purdue University.
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