Transcription factor GLK2 regulates key steps of anthocyanin biosynthesis to antagonize photo-oxidative stress during greening of Arabidopsis seedlings

Abstract

The greening of young seedling is light induced but vulnerable to photo-oxidative stress at the same time, due to the immature status of chloroplasts. Accumulation of anthocyanin is a protective response to high light, by absorbing excess energy and serving as antioxidant. In this work with Arabidopsis, we found that GARP family transcription factors GOLDEN2-LIKE 2 (GLK2), as a key regulator to chloroplast development, also plays an intensive role in regulating anthocyanin biosynthesis during seedling de-etiolation, especially under high light stress. We demonstrate that GLK2 positively regulates anthocyanin biosynthesis by directly activating the transcription of anthocyanin late biosynthetic genes (LBGs) as well as TRANSPARENT TESTA GLABRA 1 (TTG1) gene, which encodes a key component of the regulatory MYB-bHLH-WDR (MBW) complex (which also activates LBGs). Our data further show that GLK2 and MBW each could activate the expression of DFR gene (key LBG) independently, via distinct promoter regions. We therefore propose a multifaceted involvement of GLK2 in anthocyanin biosynthesis as an important protective measure for developing chloroplasts, against excessive light exposure during seedling photomorphogenesis.