The glossyhead1 Allele of ACC1 Reveals a Principal Role for Multidomain Acetyl-Coenzyme A Carboxylase in the Biosynthesis of Cuticular Waxes by Arabidopsis

A novel mutant of Arabidopsis ( Arabidopsis thaliana ), having highly glossy inflorescence stems, postgenital fusion in floral organs, and reduced fertility, was isolated from an ethyl methanesulfonate-mutagenized population and designated glossyhead1 ( gsd1 ). The gsd1 locus was mapped to chromosome 1, and the causal gene was identified as a new allele of Acetyl-Coenzyme A Carboxylase1 ( ACC1 ), a gene encoding the main enzyme in cytosolic malonyl-coenzyme A synthesis. This, to our knowledge, is the first mutant allele of ACC1 that does not cause lethality at the seed or early germination stage, allowing for the first time a detailed analysis of ACC1 function in mature tissues. Broad lipid profiling of mature gsd1 organs revealed a primary role for ACC1 in the biosynthesis of the very-long-chain fatty acids (C 20:0 or longer) associated with cuticular waxes and triacylglycerols. Unexpectedly, transcriptome analysis revealed that gsd1 has limited impact on any lipid metabolic networks but instead has a large effect on environmental stress-responsive pathways, especially senescence and ethylene synthesis determinants, indicating a possible role for the cytosolic malonyl-coenzyme A-derived lipids in stress response signaling.