<i>Arabidopsis</i> TIE1 and TIE2 transcriptional repressors dampen cytokinin response during root development.

Abstract

Cytokinin plays critical roles in root development. Cytokinin signaling depends on activation of key transcription factors known as type B <i>Arabidopsis</i> response regulators (ARRs). However, the mechanisms underlying the finely tuned regulation of type B ARR activity remain unclear. In this study, we demonstrate that the ERF-associated amphiphilic repression (EAR) motif-containing protein TCP interactor containing ear motif protein2 (TIE2) forms a negative feedback loop to finely tune the activity of type B ARRs during root development. Disruption of <i>TIE2</i> and its close homolog TIE1 causes severely shortened roots. TIE2 interacts with type B ARR1 and represses transcription of ARR1 targets. The cytokinin response is correspondingly enhanced in <i>tie1-1 tie2-1</i>. We further show that ARR1 positively regulates <i>TIE1</i> and <i>TIE2</i> by directly binding to their promoters. Our findings demonstrate that TIEs play key roles in controlling plant development and reveal an important negative feedback regulation mechanism for cytokinin signaling.