Proteolytic degradation of the flavonoid regulators, TRANSPARENT TESTA8 and TRANSPARENT TESTA GLABRA1, in Arabidopsis is mediated by the ubiquitin/26Sproteasome system

Abstract

Regulated proteolysis by the ubiquitin/26S proteasome system (UPS) has emerged as a major posttranslational control mechanism regulating transcription factor (TF) activity in plants. Anthocyanin biosynthesis in Arabidopsis is regulated by a ternary complex comprised of basic helix-loop-helix (bHLH), R2R3MYB and WD-repeat (WDR) proteins. The bHLH TF, TRANSPARENT TESTA 8 (TT8), and the WDR protein, TRANSPARENT TESTA GLABRA1 (TTG1), are essential for expression of late flavonoid biosynthesis genes. Previous studies have demonstrated that the turnover of several anthocyanin pathway regulators is controlled by the UPS. Here, we showthatTT8 and TTG1areshort-lived and targeted by the UPS for degradation. Our findings further extend our understanding of the role of the UPS in the regulation of anthocyanin biosynthesis in plants.