The transcription factor WRKY13 activates BRUTUS to maintain iron homeostasis in Arabidopsis

Iron (Fe) is a fundamental micronutrient for plant and animal physiology. Consequently, Fe limitation in agricultural systems not only compromises crop productivity but also poses a significant threat to human nutritional security. Due to the limited bioavailability of Fe in the soil, plants have evolved adaptive strategies that can regulate Fe absorption and internal balance, thereby optimizing their survival ability under Fe-deficient conditions. BRUTUS (BTS), an Fe sensor possessing E3 ligase activity, acts as a negative regulator of the Fe deficiency response by targeting bHLH subgroup IVc transcription factors for degradation. In this study, we employed yeast one-hybrid screening to identify WRKY13, an Arabidopsis transcription factor that directly regulates BTS transcription. The expression patterns of WRKY13 and BTS exhibited similarity during the transition from Fe deficiency to Fe resupply. WRKY13 mutants display increased tolerance to Fe deficiency, whereas WRKY13 complementation lines reverse the tolerance of wrky13 mutants to wild-type levels, effectively reversing the mutant phenotype under Fe-deficient conditions. Furthermore, WRKY13 was found to directly activate BTS expression by binding to W-box motifs within the BTS promoter region. Genetic analysis positioned WRKY13 upstream of BTS within the Fe homeostasis pathway. Collectively, our findings indicate that Fe deficiency stress induces WRKY13 expression, which in turn directly activates BTS transcription to maintain cellular Fe homeostasis. In addition, upon Fe resupply, WRKY13 potentiates BTS transcriptional activation, thereby fine-tuning Fe uptake and preventing potential toxicity caused by Fe overload.