BIOTIN ATTACHMENT DOMAIN-CONTAINING proteins, inhibitors of ACCase, are regulated by WRINKLED1

WRINKLED1 (WRI1) is a transcriptional activator that binds to AW boxes in the promoters of many genes from central metabolism and FA synthesis, resulting in their transcription. BIOTIN ATTACHMENT DOMAIN-CONTAINING (BADC) proteins are homologs of BIOTIN CARBOXYL CARRIER PROTEIN (BCCP) that lack a biotin-attachment domain and are therefore inactive. In the presence of excess FA, BADC1 and BADC3 are primarily responsible for the observed long-term irreversible inhibition of ACETYL-COA CARBOXYLASE (ACCase), and consequently FA synthesis. Purified WRI1 bound with high affinity (Kds in the low nanomolar range) to canonical AW-boxes from the promoters of all three BADC genes. Consistent with this observation, the expression of BADC1, BADC2 and BADC3 genes and BADC1 protein levels were reduced in wri1-1 relative to wild type (WT), and BADCs gene expression and BADC1 protein levels also were elevated upon WRI1 overexpression. The double mutant badc1badc2 phenocopied wri1-1 with respect to both reduction in root length, and elevation of indole-3-acetic acid-Asp (IAA-Asp) levels relative to WT. Overexpression of BADC1 in wri1-1 decreased its IAA-Asp and partially rescued its short-root phenotype demonstrating a role for BADCs in seedling establishment. That WRI1 positively regulates genes encoding both FA synthesis and BADCs i.e., conditional inhibitors of FA synthesis, represents a coordinated mechanism to achieve lipid homeostasis in which plants couple the transcription their FA synthetic capacity with their capacity to biochemically downregulate it.\n\nOne sentence summaryWRI1 regulates genes encoding both fatty acid synthesis and inhibitors of FA synthesis (BADCs), creating a lipid homeostatic mechanism in which the transcription of FA synthetic capacity is coordinated with the capacity to biochemically downregulate FA synthesis.