Abstract:

Subgroup 4 of R2R3-MYB transcription factors (TFs) consist of four members,MYB3, MYB4, MYB7 and MYB32, which possess the conserved EAR repression motif (pdLHLD/LLxiG/S) in their C-termini. Here, we show that MYB3 is a newly identified repressor in Arabidopsis phenylpropanoids biosynthesis. However, the repression mechanism of MYB3 is completely different from MYB4, MYB7 and MYB32. Yeast two hybrid screening using MYB3 as a bait isolates NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED1 (LNK1) and LNK2, members of a small family of four LNK proteins. The repression activity of MYB3 to cinnamate 4-hydroxylase (C4H) gene expression is directly regulated by co-repressors LNK1 and LNK2, which could facilitate binding of MYB3 with C4H promoter. The two conserved Asp residue in both region 1 and 2 domain of LNKs are essential to mediate protein-protein interaction. Importantly, the Extra N-terminal Tail (ENT) domain play a negative role in LNK-MYB3 transcription complex-dependent repression of C4H gene. We conclude that LNK1 and LNK2 act as transcriptional corepressors necessary for expression of the phenylpropanoids biosynthesis gene C4H through recruitment to its promoter via interaction with MYB3.

Key words:

Anthocyanin, Arabidopsis thaliana, phenylpropanoid pathway,transcription factor, yeast two hybrid